Monday, September 28, 2009

Revenge of the Nerds: The Story of Precocious Atlantic Salmon Parr

Native Atlantic salmon parr, Bond Brook, Kennebec River, Augusta, Maine. Watercolor, gouache and pencil. Douglas Watts, 1999.

By Douglas Watts
Augusta, Maine
September 2009

A fascinating aspect of Atlantic salmon is the existence of precocious parr.

Atlantic salmon live in the streams where they were born until they are two years old. In the spring of their third year, when they are 6-7 inches long, they turn bright silver, their kidneys and other organs undergo a profound change to let them live in saltwater, and they head out to sea for two years, whereupon they return to their natal stream to mate and spawn as 8-15 pound adults.

But some male Atlantic salmon take a different path. In the fall of their second year, they become sexually mature while still only the length of a dollar bill. Because baby salmon in freshwater are called "parr" (a very old Scottish word), these prematurely sexually mature males are called precocious parr.

In any given Atlantic salmon river, only a small number of the baby male salmon become precocious. Most do not develop testes and sperm (fish sperm is called "milt" and looks much like human semen) until they are 4 years old and have spent two years at sea.

The existence of precocious Atlantic salmon parr offers an insightful window into the mechanics of evolutionary biology. To look into this window, we need some background on the basics of the Atlantic salmon's life history.

Atlantic salmon are anadromous fish, which means they are born in freshwater but spend most of their adult life in saltwater, returning only to freshwater to mate and spawn. Atlantic salmon adults have developed an amazing ability to return from their two year stint in the ocean to almost the exact river or stream (or river and stream section) where they were born in order to mate and spawn. How salmon do this is still not known, but smell is considered the most likely candidate. Somehow, salmon can remember the "smell" of their birthplace and unerringly follow it back to where they were once babies. Other anadromous fish such as alewives and shad also share this "homing" ability.

Most Atlantic salmon return to their home rivers in the spring and summer of their fourth year, having spent two years in freshwater and two years in saltwater. In the late fall, the female salmon select nesting sites in the shallow tails of large pools in their natal rivers. These sites are chosen with great care because the fertilized eggs of salmon must remain in the riverbed for 5 months, from late fall to the next spring, before hatching into baby salmon. To build the nest for her eggs (called a "redd," another Scottish word), the female turns on her side and vigorously flaps her tail and body to create a powerful current of water directed at the stream bottom. The force of this jet of water causes the stones on the stream bottom to become momentarily suspended in the water column, whereupon the stream current carries them a short distance downstream. As you can imagine, for this technique to work, the female must choose a nesting site with just the right sized stones (about the size of tennis balls) and with enough current to carry them a small distance downstream once they are dislodged by the shaking of her tail. These sites are invariably located at the end of a pool, just above a small riffle or rapids, where the water becomes shallow and current begins to accelerate before it spills over the riffle just downstream.

This photo shows a 30 inch female Atlantic salmon turning on her side and digging her second redd in Bond Brook, Kennebec RIver, Augusta, Maine. Her first redd is visible at the far right.

After many hours of turning on her side and fanning the water vertically, the female creates a depression in the stream gravel that is roughly 1.5 - 2 feet in diameter and 1 foot deep, with excavated stones in a loose pile just downstream. It is at this point that she selects a male salmon as her partner. The male and female salmon, positioned alongside each other, pointing upstream with their sides touching, then go into a series of brief, quivering mutual orgasms which culminates in the female discharging her eggs into the depression in the gravel and the male simultaneously discharging his milt onto them. Both the eggs (which are the size of small peas) and the milt are somewhat heavier than water, and if everything goes right, the sexual act ends with a kettle-sized depression in the gravel filled with several hundred eggs blanketed and covered in pearlescent milt. This is repeated until the female determines that the depression is sufficiently filled with eggs. She and the male then break off and the female swims a few feet upstream of her nest and repeats the digging process with vigorous beats of her tail. But this time, the female is not trying to dig a nest, she is instead dislodging the stones so that the current will carry them downstream and fill in her egg-filled nest. By repeating this process for several hours, her nest becomes a humped pile of river stones with the eggs safely nestled at the bottom of a sizeable pile of loose, clean gravel. Because most female salmon carry 7-10,000 eggs, far more than one nest can accommodate, the female then digs a second nest and spawns again until she has laid all her eggs.
This photo shows a female Atlantic salmon at left, on her side digging her redd, while a large male (34-36 inches) in the center of the photo "guards" the female and her redd from other males. At the moment this photo was taken, the female had curved her body into a horseshoe and made a powerful downthrust with her tail to dislodge stones from the stream bed. The cloud of sediment from her downthrust can be seen just to the left of the male. Close examination of the male shows his distinctive pink and brick red coloration along his flanks. Large male salmon take on this color only when they are spawning. Just to the right of the male salmon is a 12 inch brown trout, which illustrates how big the male salmon is. Bond Brook, Kennebec River, Augusta, Maine, Nov. 1, 1996.
The 30 inch female salmon fully on her side at the beginning of her digging thrust. A 12 inch male brown trout can be seen in the lower right hand corner of the photo. Brown trout and Atlantic salmon are very closely related species and for this reason, male brown trout respond to the pheromones released by spawning female Atlantic salmon and will try to mate with them.

Like many animals, male Atlantic salmon aggressively compete with each other for the right to mate with females. Male salmon compete by "claiming" a female as she is digging her nest and then trying to drive all other interested males away from the nesting site. While male salmon do not bite each other, they will use their heads and snouts (which become curiously enlarged and curved at spawning season) as battering rams to "head butt" a particularly obstinate competitor. As a rule, the larger male tends to win these competitive displays and the smaller male (or simply less aggressive male) moves away to find another available female or to wait on the sidelines for a rematch. In cases where three or more males are vying for one female, these competitive matches are tumultous, with the male salmon chasing each other up and down a pool and in the shallows. This frenzy can continue for several days, especially if additional males arrive in the area after being driven off by other males at nests up or downstream, or as fresh males arrive from the ocean. The male battles only end when all the females in the area have spawned.

Enter stage right our little friends, precocious parr. Precocious parr are sexually mature male Atlantic salmon, but are only the length of a dollar bill. They are only two years old (rather than four), and have never gone to the ocean. Adult male salmon which have gone to sea and back are big fish, anywhere from 28-44 inches long and weighing from eight to 40 pounds. They have swam from their home rivers more than 2,000 miles to their marine feeding grounds near Greenland and back, growing from 7 inches long to nearly 3 foot long in just two years. Most of their compatriots on this long migration did not survive, but were eaten by larger ocean predators at some point in their journey. These large males are the veterans, the survivors, are in the peak of condition, have a tummy full of milt and only one objective: to win a female salmon against all competitors and to pass along their genetic legacy.

So how does a precocious salmon parr that weighs a few ounces and is barely the length of an adult salmon's tail have any chance of competing for and winning a female? Isn't this totally wacky?

Precocious male salmon parr do this by using their tiny size as an asset. Their secret weapon is as comical as it is effective. Here's the secret: during all of the time the big, giant male salmon are chasing each other around, fighting and vying between each other for "possession" of the female salmon and her nest, the precocious parr wait in the wings for the big males to be preoccupied with fighting other and then stealthily swim into the nest itself and sidle up alongside and underneath the female's abdomen, much like how a remora swims underneath the belly of a shark. Then they wait.

The only time I have seen precocious parr mate with a female salmon is when there were also large males around, and a large male with the female. In these cases the precocious parr sidles up underneath the female's belly, waits for the female and large male to simultaneously emit eggs and milt and then the precocious parr emits his (much smaller) package of milt at the same time, which then settles into the nest with the eggs and the large male's milt. Interestingly, even though the tiny parr has a lot less milt to squirt onto the eggs than the large male, his abdomen is much closer to the eggs, because he positions himself underneath the female which places him just a few inches above where the eggs are deposited.
Sunrise on the Kennebec River at Hallowell, Maine.

Evolutionary Persistence of Precocious Parr

The reasons why and how precocious salmon parr exist must be viewed from the perspective of the selfish gene (Dawkins 1976) and not to their utility to the species as a whole. From a "selfish gene" perspective, the precocious parr have only one aim: to ensure their genetic legacy is passed onto the next generation.

The most obvious advantage of precocious parr-ness is that they can avoid waiting until they are 4 years old to spawn, and instead spawn when they are only two years old. As important, the male parr does not have to undertake a 2,000 mile journey in the open ocean before it spawns, as must its larger male competitors.

The drawbacks of precocious parr-ness are several. First, the precocious parr is so tiny that it cannot compete for females with the large adults by driving off smaller competitors (although precocious parr will aggressively drive other precocious parr away from a spawning nest). Second is that during the spawning season, precocious parr lose their secretive nature and swim around the stream in the open during the day with wild abandon, exposing them to being eaten by kingfishers and other streamside predators. This is a threat that large males do not face because there are virtually no streamside predators large enough to attack and carry off a full-sized male salmon. A second threat is that to become sexually mature, male 2+ year old salmon parr must devote approx. 20 percent of their body weight to growing testes and developing sperm and spending the fall of their second year attempting to spawn, rather than conserving their body mass and saving their stored "fitness" to survive the oncoming winter in preparation for swimming to the ocean the next spring. Several studies (listed below) show that the over-wintering survival rate of precocious parr is lower than parr of the same age which do not become sexually mature.

We know the trade-offs of precocious parr-ness must outweigh the risks because precocious parr do exist. This means that whatever genetic proclivity toward making some male parr precocious is at least successful enough to persist in the gene pool. If the disadvantages of precocious parr greatly outweighed the benefits, the genetic recipe for making them would long ago have disappeared. By corollary, we can assume there is some sort of ongoing "stalemate" between the advantages and disadvantages of precocious parr-ness because most male salmon are large four year old adults. If the advantages of precociousness greatly outweighed the disadvantages, contemporary salmon populations would be wholly or mostly made up of small males that never went to the ocean.

Two other facets of salmon behavior contribute to the persistence of precocious male parr. First is that female salmon do all of the nest building work. If males had to contribute to the nest-building effort, the precocious parr would be in bad shape, because their tiny body size keeps them from moving even the smallest river stone, while the large males can move stones just as easily as the largest females. Second is that female salmon do not seem to actively select one mate and then drive off all other suitors. Instead, females spend all of their time building their nest, while the males around them are fully occupied with trying to drive one another away from the female. The female is only "ready" to spawn when she decides her nest is finished and is large enough and deep enough to successfully hold her cargo of eggs. It is only at this time she acknowledges or interacts with the jostling males around her.
One-year-old native Atlantic salmon parr, Worromontogus Stream, Kennebec River, Randolph, Maine. Watercolor, gouache and pencil. Douglas Watts, 1999.

Why no female precocious parr?

The reason precociousness in male salmon works -- and doesn't work for female salmon -- lies in the enormous difference in size between salmon sperm cells and eggs. Salmon eggs are the size of a small pea. A 7 inch female could only hold in her a dozen or so eggs. A 7 inch male can hold in him thousands of sperm cells. In contrast, a full grown female salmon can hold from 5,000 to 15,000 eggs. From the perspective of the selfish gene, the female has a much better chance of passing along her genetic legacy by going out to sea for two years, feeding in the rich ocean environment, growing to 28-36 inches long and being large enough to carry 10,000 eggs instead of becoming sexually mature at age two, not going out to sea and carrying only 12 eggs. There is also the issue of nest building. The female salmon builds her nest without assistance from males, and it is an arduous task. A 7 inch female could only build a nest the size of a tea cup for her 12 eggs; and few if any males would be willing to use up their sperm supply fertilizing such a tiny amount of eggs. Under the selfish gene concept, the goal of the males is to use their sperm supply to fertilize as many eggs as possible, thus increasing the chance that their genetic legacy will be passed on. The more eggs you fertilize, the greater chance that at least one of the fertilized eggs lives to spawning age itself and passes on part of your legacy. Given that precociousness in male salmon is quite common and precociousness in females is unknown, we can assume that if there ever was a genetic proclivity that created precocious females, it has blinked out of existence every time it arose because it did not "work."

30 inch long, two sea-winter adult male Atlantic salmon after spawning, Bond Brook, Augusta, Maine, October 1996. Held by Nate Gray, fisheries scientist of Maine Dept. of Marine Resources.

Do females benefit from precocious parr?

In Atlantic salmon, as humans, each fertilized egg gets one half of its chromosomes from its mother and the other half from its father. From a selfish gene perspective, the female's sole interest is in the welfare of her half of the chromosomes in her fertilized eggs. While she needs a male to mate with, this is only because she needs male sperm cells to ensure that her half of the chromosomes is passed on to her children. In this sense, the female doesn't really care whether her eggs are fertilized by a 24 inch, 36 inch, 40 inch or 6 inch male, as long as they all get fertilized. This is shown by the fact that female salmon do not appear to overtly select certain males as mates and refuse to mate with other males. From a purely statistical standpoint, female salmon benefit from having their eggs fertilized by multiple males because it increases the chance that at least some of the eggs will carry beneficial genetic adaptations from the male and have a better chance of living to adulthood and spawning. The idea is the same as betting on 6 numbers on the roulette wheel rather than putting all your money on one.

Second breach of Edwards Dam, Kennebec River, Augusta, Maine, August 12, 1999.
Kennebec River at Augusta, Maine, July 2000, one year after removal of the Edwards Dam. The dam was located in the upper center of the photo.
Male vs. Female salmon Imperatives

A large male Atlantic salmon contains millions of sperm cells, enough to fertilize all of the salmon eggs deposited by every female in a salmon river. A female, in contrast, carries between 5-10,000 eggs. From a purely statistical standpoint, it is in the female's interest to have her eggs fertilized by multiple males, which allows her genetic legacy (half of the chromosomes in each egg) to benefit from any potential genetic advantages contained in the various males in the river.

Male salmon have a powerful motivation to prevent other males from spawning with females, because every egg fertilized by another male is one that he did not fertilize. The female, on the other hand, benefits from having multiple males fertilize her eggs. This helps to explain why males devote all their time on the spawning beds to driving away other males from a female; and why females show little interest in selecting one male and spurning others.

This also helps to explain the existence of precocious salmon parr. Under the rules described above, the female benefits from having a precocious parr sneak under her belly just as she emits her eggs and casting his small cargo of milt onto them, even as the large male is next to the female doing the same thing. The large male does not want the precocious parr anywhere near the female when she is releasing her eggs because he wants to make sure that only his milt touches and fertilizes all of her eggs. By hiding underneath (or on the opposite side) of the female as she emits her eggs, the precocious parr stands a good chance of not being noticed by the large male and is able to eject his milt at about the same time as the large male ejects his milt, creating the opportunity that at least some of the parr's milt will reach an egg and fertilize it, thereby thwarting the large male's efforts to fertilize all of the eggs himself.

30 inch Atlantic salmon at mouth of Bond Brook, Kennebec River, Augusta, Maine, July 2005.
Species benefits of precocious parr

An important rule of evolutionary behavior is that individuals of a species do not do things to benefit the species as a whole. Each individual is trying to pass on their own individual genetic legacy and that is it. To the extent that one individual's efforts to pass along his or her own genes creates inherited adaptations that are spread through a population, you can (very cautiously) examine how adaptations that help one individual pass on their genetic legacy can ultimately increase the fitness of a larger group of individuals. This is especially true where some type of calamity has caused a drastic reduction in localized population size.

Female Atlantic salmon digging her spawning nest in upper Bond Brook, Kennebec River, Augusta, Maine, October 1998.

This fact was made apparent to me in 1998 in Bond Brook in Augusta, Maine. Bond Brook is a very small (25 square mile) watershed which enters the Kennebec River just below the site of the Edwards Dam, an impassable structure built in 1837 that almost completely wiped out the Kennebec River's Atlantic salmon population. The dam was removed in 1999. For several decades prior to 1999, Bond Brook was one of the only places below the Edwards Dam that contained quality Atlantic salmon spawning and nursery habitat, and for this reason, a dozen to several dozen adult salmon would swim up the brook each fall and spawn. These few salmon represented the last, tiny struggling remnant of the Kennebec's original salmon population, which exceeded 100,000 adults prior to the construction of the Edwards Dam in 1837.

In 1996 I located a previously unknown Atlantic salmon spawning area several miles up Bond Brook in a remote, roadless area that required a long, muddy walk to reach. In this reach, the habitat was nearly pristine and ideal for spawning salmon and their young. In late October 1998 I hiked into this habitat and was very pleased to find a large female digging her nest, accompanied by two large males, who fought and chased each other constantly for control of the lone female. Hiding in the tall grass next to the brook bank, I was able to spend several hours observing the stream and the salmon without being noticed, even though the salmon were only 15 feet away from me. During this time, I noticed a dozen precocious male salmon parr swimming all around the female's nest, constantly chasing each other away from the nest and vying for "ownership" of it, even as the two large males did the same thing to each other. The precocious parr behaved exactly toward each other as the two large males toward each other. They all viewed each other as competitors and rivals for possession of the nest and the female salmon building it.

What struck me was that in such a depauperate, remnant salmon population (with only one female and two large males in this stretch of brook and a total population of perhaps 30 adults), the addition of the dozen precocious parr I saw darting about greatly increased the effective breeding population of the brook. From the female's perspective, a fertile male is a fertile male, even if one is 30 inches long and the other is only 6 inches long. It is in the female's interest to have her eggs fertilized by as many different males as possible. If there were no precocious parr in the stream reach I observed in 1998, the female's eggs would at best be fertilized by two males, and perhaps only one, if the larger male was successful at driving the smaller male away and fertilizing all of the female's eggs. With the dozen precocious parr present, and because of their sneaky way of swimming underneath the female's belly without being noticed by the large males, the female's eggs had the opportunity of being fertilized by as many as 14 different males. While each baby salmon that hatched in spring 1999 from this site would have the same mother, they would have perhaps as many as 14 different fathers.

Large male and female Atlantic salmon just above the female's spawning redd in Cobbosseecontee Stream, downtown Gardiner, Maine, November 1997. I took this photo 25 feet up in a red maple tree. On this same afternoon, I observed several precocious male salmon parr occupying the redd below.

Precocious Parr, Genetic Drift and Bottlenecking

Animal populations reduced to extremely small sizes must mate with closely related members of the population or go extinct. They have no choice. This fact is especially pronounced in Atlantic salmon, which display a tightly focussed homing instinct to the stream and river of their birth and in doing so increase the chance of mating with close relatives. In a large, healthy salmon population with hundreds of fertile males and females in a short reach of river, the chance of a full sibling mating is quite small because it requires, by pure chance, a male salmon selecting his sister even in the presence of dozens or hundreds of other females who are more distantly related. But in a very small, impoverished salmon population, where only a handful of males and females spawned, there is a very high likelihood that many of the males and females returning four years later are full or half siblings. Given the choice of spawning with a sibling or not spawning at all (and not passing on their genetic legacy), the salmon must spawn with "who they brought." Over time, such a pattern of repeated sibling mating can have a very negative effect, which is well known in humans via cases of human incest. Sibling mating is bad because many diseases and birth defects are caused by the mother and father sharing the same rare, debilitating gene which is only activated when an offspring inherits it from both its mother and its father. When distantly related males and females mate, the chances of both having this debilitating gene are very low. But if the mating pair are siblings, the chance that both have the defective gene can be quite high.

Large Atlantic salmon trying leap over an impassable 1850s dam on Cobbosseecontee Stream, Gardiner, Maine, Nov. 11, 1996. The dam is still impassable.
An analogy is a deck of cards. Let's say you play a card game where each player draws a card and places it on the table. If the cards match exactly, both players "die." If the cards don't match both players "live." In such a game the risk of living and dying is dependent on the number of cards in the deck. With a 52-card deck, the players might have to go through many full decks to each throw down the same card at the same time. But now add a variation. Each time the players go through a full deck without getting a match, each has to remove some cards from their deck (say, remove all the kings, then the queens, then the jacks, and then all the 10s, etc.) With every round of the game, the chance that the players will throw down the exact same card increases because they always share the same set of cards but the total number of cards decreases. As the deck grows smaller and smaller, the chance that both players will throw down the same card approaches unity. This is a rough analogy to the effects of genetic "bottlenecking" due to a greatly reduced population size where genetic variation is sharply reduced because of the need for close relatives to mate with each other or not mate at all.

Now let's add precocious parr to our card game. Let's assume that each time a male and female "player" goes through a full deck without losing (ie. throwing down a matching card) is equal to one spawning season for Atlantic salmon. Because our game assumes a rapidly declining population of adult salmon (due to losses of adults and juveniles at dams, from human capture), we invoke a penalty after each game where each player removes all of the cards of one number before starting the next round, leaving them with fewer cards, and fewer chances of a mismatch (and their offspring living) and a greater chance of an exact match (and their offspring having a genetic defect and dying). Because an adult female having her eggs fertilized by a precocious male parr eliminates the chance of sibling mating (by definition a 2 year old precocious parr is not a sibling of a mature 4 year old female), the addition of precocious parr to the spawning stream decreases the chance of a female mating with a sibling male.

We can approximate this change in our card game by reducing (by some number) the amount of cards each side loses after each round of the game from what it would be if precocious parr were not present and available to mate with adult females. This is because, without precocious salmon parr, the chance that a 4 year old female and 4 year old male being siblings in a very depressed salmon population approaches one, and the increase in the chance of deleterious genetic defects and diseases due to sibling mating increases dramatically.

Using our card game as an analogy for the genetic shuffling between male and female Atlantic salmon, precocious parr are an important buffer against the tendency of a declining salmon population to enter a genetic bottleneck where siblings increasingly tend to mate with direct siblings, resulting in a continued reduction in genetic variation and an increase in harmful defects caused by the mother and father each having copies of the same harmful gene.

Precocious parr cannot mate with their siblings

Due to the two-year separation between precocious male parr and their 4-year-old female mates, it is impossible for precocious parr to ever mate with their sisters. This is because only male salmon are precocious and all of their sisters must reach age 4 before they reach spawning age. When the precocious males are trying to spawn at age 2, their sisters are nearby in the same stream, still two years away from reaching sexual maturity. In contrast, nonprecocious male parr and their sister parr each spend two years in the ocean before returning together to spawn at age 4. This creates a fairly high chance (especially in small, impoverished populations) that brothers and sisters will mate. In a large, healthy population the chance of direct sibling mating is greatly reduced by the large number of available, unrelated male and females in any river reach. While sibling mating in a large river population is statistically possible (and undoubtedly happens), the number of matings between unrelated salmon is much larger. In a very depressed salmon population where most of the juveniles arise from a handful of closely related adults, sibling mating becomes the rule rather than the exception.

Precocious parr and newly established salmon populations

Precocious parr should assist the establishment of persistent Atlantic salmon populations in unoccupied habitat (in contrast to the "the last survivors model" described above, this model would be the "first pioneers" model). While Atlantic salmon have an acute homing instinct which causes them to return to the river reach where they were born, some Atlantic salmon break from this instinct and explore and colonize suitable habitat where few, if any, salmon are present. This "straying" instinct is well documented in Atlantic salmon, although it is adopted by only a small (1-5 percent) of salmon, with most (95 percent) returning to the same river, stream and even gravel bar where they were born (Baum 1997).

A pioneer group of Atlantic salmon colonizing an uninhabited stream is comprised of just a few spawning males and females. The success of this colonization effort depends on the progeny of the first pioneers surviving in the stream to adulthood and returning to the same stream to spawn. In such a nascent population, sibling and half sibling mating is practically guaranteed.
Precocious salmon parr provide a unique opportunity for newly established salmon populations to "mix-up" their mating combinations by allowing cross-generational spawning between 4 year old females and 2 year old males. This greatly reduces the chance that all of the offspring in an early spawning generation are produced by the mating of siblings or half siblings.

Close-up of male two sea-winter Atlantic salmon, approx. 30 inches long, Bond Brook, Augusta, Maine. You can tell this male has completed spawning because his coloration has started to become greyish. During the height of spawning the males have a ruddy pink coloration along their sides.

The needs of the "selfish genes" of Atlantic salmon

In this era of Atlantic salmon populations approaching extinction, the primary focus of Atlantic salmon biologists and conservationists is on the preservation of Atlantic salmon populations rather than the welfare of any one individual Atlantic salmon (although obviously the former is completely dependent on the latter). Evolutionary biology requires us to examine Atlantic salmon strictly through the lens of individual salmon trying to preserve their legacy by surviving to spawning age, mating, and giving birth to salmon that also spawn. This is especially true in the case of precocious male salmon parr. While we can theorize or surmise that precocious parr increase the fitness of a local population, stave off the extirpation of depressed populations, and increase the chance that newly established populations will persist, we cannot forget that the genetic adaptations which allow 2+ male salmon parr to be sexually mature two years earlier than most of their cohorts was not "designed" for these purposes. A more appropriate way of characterizing this genetic adaptation is that it has persisted in Atlantic salmon populations because in some statistical way it confers a neutral or positive survival advantage to those salmon who are born with it; and that the "success" of this peculiar life history strategy can be estimated by its prevalence or absence in the gene pool of Atlantic salmon today. Presumably, in Atlantic salmon populations decimated by long-term anthropogenic effects (as in the U.S.), if precocious parr provided a neutral or negative benefit to survival of their offspring, it would have disappeared from the remaining gene pool of U.S. salmon. By an admittedly speculative analytical basis, the adaptation of precocious parr seems to provide individual Atlantic salmon in highly depressed remnant populations an important hedge against the environmental and genetic forces which conspire to drive remnant populations to increased dimunition and extirpation.

Precocious parr mitigate against harmful environmental effects face by young salmon as they try to migrate downstream as smolts and live in marine waters for two years before they return to spawn. This is accomplished by allowing some male 2+ parr reaching sexual maturity in their own natal stream without having to live to age 4 or survive a perilous 2 year journey back and forth across the Atlantic Ocean to their feeding grounds near Greenland.

The adaptation of precocious parr mitigates against the harmful effects of genetic bottlenecking and genetic drift in small, declining, remnant Atlantic salmon populations by reducing the chance that most or all returning adult salmon are forced to mate with their sisters and brothers or not mate at all. Precocious male salmon parr have a unique life history because they mate at age two with females that are age four or older. This guarantees that they will not mate with their siblings or close relatives. The presence of numerous precocious parr in an impoverished Atlantic salmon spawning stream greatly increases the effective population size of the stream by greatly increasing the number of potential fathers for the available females' egg cargo. Due to their young age, precocious parr have different mothers than the females they try to mate with and the adult males they compete with. This means precocious parr increase the effective population size of mothers in a given stream because they do not share a mother with any of the adult males and females. In contrast, in a very depressed and small population, it is possible that most of the adult male and female salmon have the same mother.

Wild Atlantic salmon parr, Worromontogus Stream, Randolph, Maine, October 1996. This is an "0+ parr" meaning it has had one summer of growth after emerging from the gravel that spring. This parr would overwinter, spend the next summer in the stream as a "1+ parr", overwinter again and become a smolt the next spring and head out to sea.

A Theory Explaining Precocious Male Atlantic Salmon Parr

It is likely that all male Atlantic salmon carry the necessary genes to allow them to become precocious, ie. to become sexually mature prior to migrating to sea as smolts. It is also possible that this gene for precociousness tends to be triggered by the relative presence or absence of male salmon testosterone in a salmon spawning stream. A spawning stream occupied by a large number of adult males carries a much higher "signal" of male salmon testosterone than a stream with very few adult males. If the presence of salmon testosterone inhibits the genetic expression of precociousness in 2+ male salmon parr, the number of male parr in the stream displaying precociousness would be higher if there were few adult males.

Such an environmental triggering would explain why recent field research shows a higher incidence of precociousness in small, depressed Atlantic salmon population lacking adult males and a lower (observed) incidence of precociousness in salmon populations with a large number of adult males. Support for this theory is shown by the fact that male brown trout (Salmo trutta) and brook trout (Salvelinus fontinalis) typically become sexually mature at age 2-3. Two sea-winter Atlantic salmon become sexually mature at age 4, three sea-winter salmon at age 5 and male grilse at age 3. In contrast, sexually mature female anadromous Atlantic salmon less than age 4 are extremely rare. Among brook trout and brown trout, its closest cousin species, sexual maturity for male Atlantic salmon at age 2 is the norm, ie. the age at which precocious salmon parr become sexually mature. Only in healthy anadromous Atlantic salmon populations do males tend to delay their sexual maturation until age 3, 4 or 5. This suggests an environmental inhibiting factor keeps most anadromous male Atlantic salmon from exhibiting their "normal" sexual maturity at age 2 and delays it until age 3, 4 or 5; the existence of precocious parr suggests a relaxing of this inhibition; and this relaxation is expressed most prominently when a local population lacks adult males. From this we can deduce an inverse relationship between the number of precocious parr in a spawning stream and healthy survival conditions for those male Atlantic salmon which go to sea before spawning.

Large Atlantic salmon, Cobbosseecontee Stream, Kennebec River, Gardiner, Maine. Nov. 11, 1996.

UPDATE: A recent research study of southern European salmon populations (Garcia-Vazquez et al. 2001) seems to confirm the above theories of species benefits in depressed Atlantic salmon populations from the presence of precocious male parr. The study states in part:

"Mature juvenile males may have saved south European Atlantic populations from extinction, given the depressed size of populations for a number of decades. This point suggests that these populations may be under intense selection for maturation of juvenile males, and hence that the relative preponderance of mature juvenile males in the southern populations may be an adaptive response to anthropogenic depletion of anadromous salmon numbers .... In conclusion, precocious Atlantic salmon parr contribute to balance the sex ratio, enlarge the effective population size, and increase outbreeding. In addition, they fertilize most eggs in the interspecific matings between Atlantic salmon and brown trout. Sneaking behavior has not been evidenced in small maturing brown trout, this being the main reproductive difference between brown trout and Atlantic salmon in wild southern European populations."

Works Cited:

Baum, E.T. 1997. Maine Atlantic Salmon: A National Treasure. Atlantic Salmon Unlimited. Hermon, Maine.
Dawkins, R. 1976. The Selfish Gene. Oxford University Press. London, England.
Garcia-Vazquez, E., P. Moran, J. L. Martinez, J. Perez, B. de Gaudemar, and E. Beall. 2001. Alternative Mating Strategies in Atlantic Salmon and Brown Trout. The Journal of Heredity 2001:92(2).
Myers, R.A, J.A. Hutchings. 1987. Mating of Anadromous Atlantic salmon, Salmo Salar L., with mature male parr. J. Fish Biol. (1987) 31, 143-146. PDF here.
Saura, M. et al. 2008. Impact of precocious male parr on the effective size of a wild population of Atlantic salmon. Freshwater Biology. Vol. 3 No. 12. pp. 2375-2384. Blackwell Science, Oxford.

Mark Kemezys (1961-2009) at the ledges and falls at the head of tide of Bond Brook, Kennebec River, Augusta, Maine in spring 2005. For more than 150 years, Bond Brook provided the only accessible habitat for Kennebec River salmon below the impassable Edwards Dam. A native of Norridgewock, Maine, Mark spent many hours cleaning up trash and debris along the Kennebec River at the "yellow stairs" in downtown Augusta.

Wednesday, September 16, 2009

Caratunk Falls and "The Cut" at Kennebec River, Solon, Maine.

Unlike the U.S. Midwest, South and West, Maine has largely been spared from the destruction of its rivers by pork barrel "river improvement projects" by the U.S. Army Corps of Engineers during the post World War II period. One river that was not spared was the Kennebec River in Solon, Maine.

At some time in the 1950s, the Army Corps, with the consent of the State of Maine and lumber and paper mills, dug an enormous canal called "The Cut" on the Kennebec River in Solon below Caratunk Falls. This "cut" dewatered the mile-long, naturally curving channel of the river and replaced it with a ruler-straight, high-walled ditch from Caratunk Falls to the Route 8 bridge over the Kennebec just above the Evergreen Campground.

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A Google Map aerial image of "The Cut" on the Kennebec River in Solon, Maine. The original, natural Kennebec River channel is to the right.

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This aerial closeup shows the large natural pool at the base of Caratunk Falls (with the Williams hydroelectric dam built on top of the ledges), the beginning of "The Cut" at the bottom and the natural channel of the Kennebec River at the right, almost completely dewatered.

The black and white photograph at top shows the Kennebec at Solon immediately before "The Cut" was created. It is from a postcard I purchased at an antique store in Hallowell, Maine. On the back of the postcard is a ball point pen inscription which says "Aug. 7, 1951" which I am assuming is close to the year when the photo was taken. The position of the photographer suggests it was taken on the left hand bank of the Route 8 bridge. In the distance in the center of the photo you can see the buildings of downtown Solon on the high bank.

A closeup from the original photo suggests the main channel was the right hand channel that is now dewatered by "The Cut" and this channel was extremely wide and shallow. A second channel enters from the left. This channel was the route chosen by the Army Corps to "straighten out" the river channel, which resulted in "The Cut."

Why and when was "The Cut" created?

During the late 1990s, I represented Friends of the Kennebec Salmon in the relicensing of the Anson and Abenaki hydroelectric dams in Madison, Maine, located on the Kennebec River about 12 miles downstream from Solon. It was at this time I learned of "The Cut" and began doing historic research on when and why it was created. Historic documentation on this massive river channelization project is virtually non-existent. Its name ("The Cut") is the local name, and from talking to longtime residents of the area, I learned it was made at some time in the 1950s and was an Army Corps of Engineers project. The photo postcard above, with a date of August 1951 written in pen on the back, would seem to fix its construction date to after 1951. Despite an exhaustive microfilm search of Maine newspapers for this period at the Maine State Library, I could not find a single news article announcing or discussing this project. Obviously, some records and recollections exist of its construction, but to date they have been elusive.

As best as I can figure, "The Cut" was made to more effectively move logs down this section of the Kennebec River. The 1950s were the apex of massive log drives of pulp wood down the Kennebec River to paper mills in Madison, Skowhegan, Fairfield, Waterville and Augusta. These logs were very uniform in length and width: four feet long and six to eight inches in diameter. As many historic photos attest (and several early movies show), the entire Kennebec River, from bank to bank, would be carpeted with these millions of these pulp logs from ice-out to early summer each year until the log drives finally ended in 1976.

Driving large sawlogs over Skowhegan Falls, middle Kennebec River, late 19th century. Prior to dam building, 100,000 Atlantic salmon leaped up these falls every spring and summer. Skowhegan Falls no longer exists. It was replaced by a hydroelectric dam in the 1930s.

A constant bugbear of log drivers was the numerous side channels and shallow riffle and shoal areas of the Kennebec, which is especially pronounced in the river from Solon to Madison. During high spring run-off, at the beginning of the annual log drives, the logs flowed easily and freely down these channels. But as the spring run-off subsided, these side channels and riffles would become just a few feet deep (or less) and result in the stranding of tens of thousands of pulp logs, forcing log drivers to wait for a rain storm to bring the river back up, or the loss of the lumber.

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This recent aerial photo of the Shawmut Dam on the Kennebec River in Fairfield and Clinton, Maine shows how "boom islands" were used to guide pulp logs over the dam and to keep them in the main current and out of "backwater" areas where they would get waterlogged and sink to the bottom. The bright white area in the middle of the dam spillway (which crosses the river diagonally) is the sluice that allowed pulp logs to pass over the dam.

Judging by the early 1950s postcard of the Kennebec at Solon, the two channels of the Kennebec River below Caratunk Falls at Solon were very wide and shallow except at spring flood flows, especially right channel, which hugs the steep hill upon which the town of Solon was built. It seems likely that "The Cut" was created to get rid of this persnickety, log-snagging section of river channel and to replace it with a perfectly straight and very deep channel that was designed as a very effective pulp log delivery device. The perfectly straight path of "The Cut" has all the earmarks of a post WWII Army Corps project.

Caratunk Falls: a Former Natural Wonder

Charles G. Atkins, Maine's first Fisheries Commissioner, wrote the following in his first report to the Maine Legislature in 1867:

"The fact that salmon passed Carratunk falls is worth examining. At this point the whole Kennebec rushes down over a precipice sixteen and a half feet into a deep chasm several hundred feet long and less than fifty feet wide. The depth of the chasm is unknown. Logs more than fifty feet long go down end first, disappearing with great velocity; but they are never heard to strike bottom, and after a long absence reappear, generally, it is said, the same end uppermost that disappeared first, and leap into the air, or standing upright one third or one half submerged, go whirling down the chasm.

Those who have witnessed the ascent of salmon say that one was first seen to leap several times a few feet out of water a little way down the chasm. He was then seen to emerge from the water a few feet from the fall and obliquely towards it, with such velocity as to rise twelve or thirteen feet through the air, and strike head first the face of the falling water at that height. If he struck the water in a line with its motion a sort of hesitancy was observed, and then in a moment he moved forward and over the crest of the fall; but the least deviation from a true line sent the fish backward to try again. The same salmon (known by a mark on his back) was seen to try to leap the fall six times unsuccessfully and succeed at the seventh attempt. Some observers thought that about one in three succeed in passing. It would seem that this feat must require the utmost strength of a salmon, and perhaps only the strongest would succeed.

Besides this main channel there were two smaller passages, one on either side of the river, where it is said salmon sometimes ascended, and where they were taken by dip nets. One hole is pointed out where nine salmon were once taken at a single dip. The eastern passage might be converted into an easy fishway, if the main fall should prove too difficult.

The passage at Carratunk falls was evidently rendered possible by the great depth of water from which the salmon could spring into the air, acquiring momentum enough to carry them two-thirds of the way up, and by the thickness of the falling sheet, which gave them room to swim after striking."

No Atlantic salmon has swam in the waters of Caratunk Falls since the 1840s.

First Cut is the Deepest

The last log drive on the Kennebec River was more than 40 years ago. Nobody under the age of 50 can even remember seeing the last Kennebec River log drive. Yet "The Cut" still remains. Should it?

Since I first walked along "The Cut" in 1998 and walked down the original, massive and now dry channel of the Kennebec, and then found this 1950s photo of the Kennebec at Solon before "The Cut" was created, I have advocated for filling in "The Cut" and restoring the Kennebec at Solon to its natural condition. A few reasons are as follows:

a) The entire purpose of "The Cut" (log drives) has been obsolete for 40 years.
b) "The Cut" wrecks a large section of one of the only free-flowing sections left on the middle Kennebec River (the rest of the middle Kennebec River has disappeared under the impoundments of hydro dams, ie. Wyman, Williams, Anson, Abenaki, Weston, Shawmut).
c) If restored, the natural channel of the Kennebec dewatered by "The Cut" would provide a large amount of outstanding spawning and rearing habitat for Atlantic salmon, trout and many other wildlife species.
d) "The Cut" is ugly and boring.

Tuesday, September 15, 2009

Paul Robeson, Pruden's Purple and Garden Peach tomatoes

According to the National Weather Service, June, July and August 2009 were the wettest June, July and August period in Portland, Maine since records first began in 1871. This meant a disastrous year for Maine vegetable gardens, especially tomatoes. Many people I know lost all of their tomato plants in August due to late blight, which is a fungus that thrives in wet, cool, clammy weather and can kill an entire plant or garden in just a few days. Somehow, most of our tomato plants were spared the full blown death onslaught of late blight that many neighbors suffered, and now that we have had very dry, sunny weather for the past three weeks, the blight we do have is subsiding and the tomatoes are ripening as we had hoped.

This year we planted three heirloom tomato varieties and a new open-pollinated cherry tomato developed in 1997 by a gardener and plant breeder from Garland, Maine who goes by the name "Relentless." We grew all of them from seed in late March with seeds from Fedco Seeds in Waterville, Maine, one of the best seed companies in the country. Fedco is especially useful because they specialize in vegetable varieties that have been field-proven to prosper in northern and central New England. For those of us trying to grow long season, hot weather loving plants like tomatoes and peppers in Maine, buying seeds from Fedco saves on a lot of disappointment.

The heirloom varieties are Paul Robeson (a "black" tomato originating in Russia); Pruden's Purple (very similar to Pink Brandywine); and Garden Peach, a true oddball that looks very much like a small peach and tastes very sweet. The cherry tomato variety is called "Be My Baby."

Pruden's Purple in front, Paul Robeson behind. The largest tomatoes are about a pound.

Paul Robeson Tomato

Contrary to its varietal name ("black tomato"), Paul Robeson tomatoes are not black. When fully ripe, the bottom of the fruit is a deep scarlet orange that grades into green at the stem, although some fruits will be entirely cast in a color that is equal parts orange, brown and green. The "black" moniker comes from its color when sliced, which is a dark, "smoky" shade of pinkish scarlet, almost like a rare steak. Most fruits range from 1/2 to 3/4s of a pound. Despite the horrific weather this year, our Paul Robeson plants have been quite prolific, with ripe tomatoes in late August and 6-8 large fruits per plant so far. Like most heirlooms they are "indeterminate" and require staking or caging their 5-6 foot high stems. They are very "meaty" with little watery pulp. Because of the ever present late blight this year (which thrives in shade and moisture), we learned quickly to keep the ripening tomatoes off the ground and up in the air so that the breeze and sun can keep them dry.

Pruden's Purple Tomato

Pruden's Purple is a potato leaf heirloom with very large, oval fruits (up to 1.5 pounds) that turn a deep pinkish scarlet grading into yellow orange at the stem when fully ripe. They are similar to Pink Brandywine, and contrary to their name, are not purple. Because the fruits get so big, they take a month or more to ripen and require staking and tying to keep the heavy fruits from breaking the stems. The plants are big and gangly, reaching over 6 feet tall with stems at ground level that can be almost an inch thick. The flesh is a bright, pink-scarlet that looks like an extra-reddish watermelon. Like the Paul Robeson's, the Pruden's Purple ripen slowly and the unripe fruits are susceptible to rot, slugs and blight if hidden inside the plant, near the ground and in deep shade. As a preventive measure, we have started picking fully grown fruits that are "almost ripe" (just starting to show color) and letting them ripen on a table rather than risk losing them to rot, blight and munching slugs. I like Pruden's Purple because they are almost as big as a musk melon and are beautifully colored and shaped.

Very few Garden Peach tomatoes have such a pronounced proboscis, but this one does.

Garden Peach Tomato

We grew Garden Peach tomatoes last year and found them prolific, long-lasting (right up to Oct. 17, the killing frost in Augusta, Maine), great tasting (very sweet and non-acidy) and so strange looking that we had to grow them again. People visiting our house look at the picked Garden Peach tomatoes on the table and ask, "What are these things?" Often they are quite surprised when I tell them they are tomatoes. Like a peach, they turn a bright, sunny yellow when ripe, with a blush of pink spreading from the base. And like a peach, the fruit has a tiny, but noticeable "peach fuzz" all over its skin. They are truly odd ducks and are about the only tomato I will eat raw (I'm not much for eating raw tomatoes) because they are very sweet and mild. Our plants this year got hit pretty hard by late blight and many of the half-ripened fruits turned brown and scabby on the vine. But because the plants are so prolific (think 30 or more pool ball sized fruits), we still are getting quite a lot of them.

Tuesday, September 08, 2009

Evidence of a prehistoric two-weir fish trap at at China Lake Stream, Sebasticook River, Winslow, Maine.

By Douglas Watts
Augusta, Maine
September, 2009.

Evidence since the removal of the Fort Halifax Dam in 2008 suggests the presence of a prehistoric two weir fish trap for alewives and/or American eel at China Lake Stream, Sebasticook River, Winslow, Maine.

General Locality Description:

China Lake Stream (also known as "Mile Brook" or "Outlet Stream") flows north from its source, China Lake, located in China and Vassalboro, Maine to the Sebasticook River in Winslow, Maine, one mile above the confluence of the Sebasticook and Kennebec Rivers. The stream is approx. 6 miles long.

Until 2008, the lowermost five miles of the Sebasticook River and the lowermost one mile of China Lake Stream were flooded and impounded by the Fort Halifax Dam, constructed by Central Maine Power as a hydroelectric dam in 1908. During this century-long period, the lowermost mile of China Lake Stream was a shallow and narrow pond-like impoundment with a width of 100-300 yards and a substrate of deep organic muck.

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In this satellite image, the Kennebec River flows from north to south on the far left, is joined by the Sebasticook River, flowing from the east to west, with China Lake Stream entering the Sebasticook River from south to north in the right center. This image was taken before the Fort Halifax Dam at the mouth of the Sebasticook was removed in 2008 and shows the dam's impoundment extending up the Sebasticook River and China Lake Stream. The Fort Halifax dam can be seen as the large, bright feature in the Sebasticook just before it enters the Kennebec River.

In summer 2008, the Fort Halifax Dam was removed by its owner, FPL Energy. Since the dam's removal, the flow of China Lake Stream has downcut through a century's accumulation of soft silt and sediment and the original channel has largely been restored to its natural gravel, cobble and boulder substrate. Thick (4-8 feet) beds of accumulated silt and sediment still cover the former impoundment on both sides of the newly incised channel. During the past two growing seasons these areas of rich silt and muck have dried out and have become thickly vegetated with grasses and other pioneer annual plants. This thick silt bed completely blankets and obscures the original soil surface along the first one mile of the stream.

This photo shows all of the changes caused by the impoundment of China Lake Stream by the Fort Halifax Dam since 1908 and its removal in 2008. The tree line in the background was the top of the impoundment, the grass line was the bottom of the impoundment, the stream channel shows the original channel of the stream downcutting through the silt and muck of the former impoundment, and the ledge of tightly folded Waterville slate in the foreground shows the natural hydraulic control of the streambed.

This photo shows all of the real important changes on China Lake Stream. Dan Watts and Queegueg T. Dog, Ph.D. wade through the rushing waters of China Lake Stream on July 4, 2008, where no child has been able to wade since the 1800s.

This photo shows the five foot thick bed of sawdust, muck, silt, trash and woodchips that has accumulated in the bed of the formerly impounded reach of China Lake Stream during the past 150 years. The natural shoreline of the stream is buried somewhere below the base of this stack of recent debris.

A point approx. 1/4 mile below where State Route 137 crosses China Lake Stream marks the upstream limit of the former Fort Halifax Dam impoundment. This point is approx. one mile above the stream's mouth and is marked by a mature forest (primarily hemlock) growing directly alongside the stream with no areas of impoundment inundation and sedimentation. The stone weir sites are several hundred yards below this point at the uppermost extreme of the impounding effects of the former Fort Halifax Dam. Based upon the vertical height of the "bathtub ring" along the wooded margin of the stream, it appears the site of the stone weirs was impounded by the Fort Halifax Dam by about two feet of water.

Site Description:

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This satellite image shows the weir sites at the bottom left, with China Lake Stream flowing from south to north, (bottom to top). This image was taken before the Fort Halifax Dam was removed in 2008 and shows the extent of the impoundment in China Lake Stream as well as the course of the stream's original channel, which has now been restored.

The weir site consists of the remains of two barriers made of river stone that perpendicularly traverse the channel of China Lake Stream. The two stone barriers are approximately 250 feet apart in a stream section that is especially shallow, flat bottomed and composed of golf-ball to baseball-sized cobble. The upper barrier is a 1-2 foot high "wall" of bread loaf sized river stones that completely crosses the stream except for a 3 foot wide "chute" hard on the left hand side of the stream (looking upstream). The barrier curves slightly downstream. The barrier is quite obviously manmade.

Upper weir site, low water, Sept. 8, 2009.

Upper weir site, high water, July 4, 2009.

The lower weir feature is much more fragmentary and incomplete, but in some ways is more diagnostic. It is located just upstream of a small riffle feature in the stream and at the tail of a 250 foot long, very shallow pool. At low stream flow (as observed in early Sept. 2009), approx. two thirds of the stream channel (starting from the right hand side) is dry and composed of small, evenly sized cobble. This flat cobble bar focusses the entire flow of the stream hard on the left hand bank of the stream channel, where the bank quickly climbs about five feet into a grove of mature hemlock.

Queequeg T. Dog, Ph.D. at lower weir site.

The presence of a stone weir at this lower site is conjectured because of the anomalous presence of a 3-foot wide line of large stones crossing the stream perpendicularly in the middle of the cobble gravel bar. These large stones are set deeply into the smaller cobble bar and form a roughly straight line for a distance of approx. 10 feet across the middle of the stream channel. This line of stones can only be observed at very low water. The orientation and location of the stones cannot be explained by natural sorting and scattering by the stream's flow at this location. A number of large (basketball sized) rocks are anchored hard on the left bank in a line fairly consistent with the mid-channel row of stones.

Other Evidence of Prehistoric Use and Habitation

Supporting evidence for these stone features being weir remnants is provided by two accumulations of fire cracked rock (FCR) and shards of worked Kineo rhyolite on opposite banks of the stream directly adjacent to the site of the lower weir. Extensive searches of both sides of the stream bank for 1/4 mile above and below the lower weir site during three site visits in the past year have failed to locate any FCR or flint/chert debitage. FCR quickly disappears 100 feet above and below the lower weir site on both sides of the stream bank. All of the debitage found to date is from Kineo rhyolite and is only in large rough shards, most with one side being the natural rounded surface of a glacially rounded cobble. FCR fragments outnumber debitage by about 30:1 and are most densely concentrated on the left hand side of the stream bank approx. 30 feet below the lower weir site. While shards of 19th century, glazed redware pottery are abundant in the streambed and shoreline above the site to the Route 137 crossing, no shards of prehistoric ceramic have been found in the area of the conjectured weirs.

Kineo rhyolite shard from the left hand bank of lower weir site.

Kineo rhyolite shard from the right hand bank of lower weir site.

Examination of the soil surface at the stream bank at the lower weir site shows a clear horizontal interface of hard marine clay overlain by a darker, browner, less cohesive silt layer, finally overtopped in places by a layer of finely ground sawdust, sawn wood chip fragments and woody debris, presumably deposited by 19th century sawmills (there is a breached 19th century dam approx. 1/4 mile above the weir site).

Queequeg T. Dog, Ph.D. and a stick show the horizontal interface of the 20th century Fort Halifax Dam impoundment layer of silt and original marine clay shoreline of China Lake Stream just below the lower stone fish weir. Fire cracked rock (FCR) and worked shards of Kineo rhyolite are found in the area below the "silt line," which is the natural surface of stream bank.

Are the conjectured weir sites the remains of 19th century dams or 20th century "swimming holes"?

Due to their placement, orientation and design, the two in-stream features are clearly manmade. This does not necessarily mean they were made by prehistoric people as fishing weirs. These features could have been made by European settlers. A number of independent lines of evidence rule out this possibility.

The construction of the Fort Halifax Dam in 1908 impounded and flooded the site of the two weirs by at least several feet. This eliminates the chance that the barriers were built in the 20th century by local kids as a "swimming hole." But what about a 19th century swimming hole? This can be discounted for two reasons. First, the stream reaches above either barrier are far too small and shallow to be worthy of such effort to make a 19th century swimming hole. Second, the extensive use of China Lake Stream as a conduit for industrial waste and household sewage during the 19th century would have made the stream less than desirable as a swimming hole for local youth.

Are these features the remnants of 18th or 19th century mill dams?

Wooden mill dam remnants are exceptionally well preserved if kept underwater. The sites of the stone weir features have been constantly underwater since the construction of the Fort Halifax Dam in 1908. Any timber remnants in the riverbed from a 19th century mill dam would still be well-preserved and visible in the streambed today. No timber remnants are visible in or along the streambed at the two weir sites.

A second clue is the presence of a very old, well-preserved timber dam on China Lake Stream one half mile downstream from the weir site, just above the Garland Road bridge. This dam is obviously of 19th or early 18th century vintage because it was inundated by nearly ten feet of water by the 1908 Fort Halifax dam impoundment. The design of this small dam is identical to timber dams built at the mouths of Riggs Brook, Goffs Brook and Seven Mile Stream along the Kennebec River in Augusta, Sidney and Vassalboro in the late 1700s and early 1800s. The latest date of construction of these small timber dams is the 1830s -- before the Augusta dam was built on the Kennebec River in 1837, which flooded and inundated these dams and preserved their timbers until the Edwards Dam was removed in 1999 and these dams were rediscovered.

A last clue is that by the mid 19th century, mill dams on rivers and pond outlets in the area were constructed with large, roughly rectangular pieces of quarried stone to increase hydraulic head and to reduce the chance of dam failure during freshets (Watts 2004). An example of this type of dam is found directly below the Route 137 crossing of the stream. Dam sites of this construction type are easily identified by their well-fortified abutments of cut stone in the stream bank, a well-defined "mill pond" above the dam site and the presence of large, square or rectangular stones in the streambed and banks directly below the dam site.

The weir sites lack any of the typical remnant features of a mid-to-late 19th century stone mill dam or a late 18th or early 19th century timber dam. This negative finding is strengthened by the obvious and well-preserved remnants of both types of dam immediately upstream and downstream of the weir site.

A hefty slab of Kineo rhyolite found on the bank of China Lake Stream, still showing the freshly broken surface from when it was shattered 4,000 years ago to make a spear point. In the background of the photo you can see the site of the lower stone weir (at the bend to the left) and in the far background the upper stone weir. Prior to dam construction, more than 500,000 alewives swam past this spot on China Lake Stream every spring to spawn in China Lake, and thousands of 3-4 foot long American eels migrated downstream from China Lake past this spot each fall.

Historic accounts of stone weirs for alewives

Pory (1622) and Josselyn (1647) describe the use of piles of stones in a stream to block migrating alewives to aid in their capture:

Pory writes: "In April and May come up another kind of fish which they call herring or old wives in infinite schools, into a small river running under town, and so into a great pond or lake of a mile broad, where they cast their spawn, the water of the said river being in many places not above half a foot deep. Yea, when a heap of stones is reared up against them a foot high above the water, they leap and tumble over and will not be beaten back with crudgels."

Josselyn writes: "The Alewife is like a herrin, but has a bigger bellie therefore called an Alewife, they come in the end of April into fresh Rivers and Ponds; there hath been taken in two hours by two men without any Weyre at all, saving a few stones to stop the passage of the River, above ten thousand."

Hanson (1852) describes an 18th century female settler dipnetting large numbers of alewives from Worromontogus Stream in Pittston, Maine, 18 miles south of China Lake Stream:

"It is related that alewives were so plentiful there at the time the country was settled, that bears, and later swine, fed on them in the water. They were crowded ashore by the thousands. Mrs. David Philbrook, who was a McCausland, was very much in want of a spinning wheel. One day she took a dip net, and caught seven barrels of alewives in the Togus, and took two barrels in a canoe, and paddled them down to Mr. Winslow's, and exchanged them for a wheel."

See Watts (2003) for further 18th century documents. (pdf here)

These 17th and 18th century accounts show that, in a small enough alewife stream, nothing more than a low pile of stones in a shallow riffle would create a sufficient barrier to allow for large amounts of alewives to be taken by nets and baskets. In contrast, the China Lake Stream weir sites show a more industrious intent. First, there are two weirs within a few hundred feet of each other (why not just one?). Second, the size of the structures and the time and effort taken to make them shows more than just a casual, low intensity use and purpose.

A large stone fish weir on Seboeis Stream, Piscataquis River, Howland, Maine. Photographed by Douglas Watts in extremely low water in October, 2002. This weir is still periodically used by local commercial eel fishermen to catch adult eels migrating downstream from Seboeis Lake, which accounts for its excellent condition. Given that the inverted "V" of the weir points upstream, it was most likely first built to capture fish migrating upstream (ie. alewives), which once went upstream to Seboeis Lake and other ponds in the watershed in huge numbers until the runs were extirpated by dam construction on the Penobscot and Piscataquis Rivers in the 19th century. Despite this design favoring the capture of upstream migrants, the weir was mostly likely also used to catch eels migrating downstream in the fall.

Using two weirs to create a more effective fish trap:
a design hypothesis.

The location of two prehistoric stone weir structures less than 300 feet apart across the bed of China Lake Stream suggests the possibility these two weirs were built and used in tandem to create a highly effective fish trap to catch adult alewives (Alosa pseudoharengus) migrating from the Atlantic Ocean to their spawning grounds in China Lake.

Recent excavations at the Cates Farm archaeological site at the outlet of China Lake have found alewife bones, confirming the harvest and consumption of alewives by prehistoric people at China Lake. These alewives reached China Lake by migrating from the Atlantic Ocean to the Kennebec River, up the Sebasticook River and up China Lake Stream. Modern biological studies on alewife productivity and the size of China Lake suggests the historic size of the China Lake alewife run exceeded 500,000 adult alewives each spring. Based on modern alewife runs on the Sebasticook River, the alewife run on China Lake Stream began in late April and ended in early June.

A large alewife run forced to migrate up a stream as small, shallow and narrow as China Lake Stream to reach their spawning grounds in China Lake would have created an ideal seasonal fish harvesting opportunity for prehistoric people. The weir sites located on lower China Lake Stream have the prerequisites of a preferred alewife harvesting locality. At the weir sites, China Lake Stream is very shallow (1-3 feet deep), yet narrow (less than 50 feet wide), and is only one mile above the stream's confluence with the Sebasticook River, making it easily accessible by canoe or foot from the Sebasticook, which served as a key travel highway between the Kennebec and Penobscot River drainages. It may not be coincidental that the two largest concentrations of extant prehistoric lithic artifacts on the Sebasticook and lower Kennebec Rivers is found on the Sebasticook River directly across from the mouth of China Lake Stream and a quarter mile below it.

Adult alewives have a powerful homing instinct which commits them to swimming tens or hundreds of miles to reach their natal birthplace in a specific spawning pond. To reach these ponds and spawn, alewives will spend days and weeks trying to swim over or around any obstacle in their way, be it a human-made dam, a beaver dam, a natural waterfall or a log jam in a stream.

A stone and brush fish weir is made by erecting a wall of stones across the stream bed and driving saplings, sticks and brush in between the interstices of the stones to create barrier against fish migrating upstream (alewives, shad) or downstream (adult American eel). The advantage of a stone and brush weir is that: a) water flows through the brush but fish cannot; b) the brush and saplings can be easily replaced from local materials each migration season and; c) the stone "foundation" which holds the brush and saplings can be easily repaired and maintained from stream stones each migration season.

Once a stone and brush weir is built, migrating fish are blocked by the structure and congregate in large numbers directly below it, trying to find a way past it. Once fish numbers are large enough below the obstruction, they can be easily netted, speared or caught in baskets. The problem with a "one weir" system in a streambed is that upmigrating fish quickly disperse downstream from their congregation at the upstream obstacle once people enter the stream to catch them, and only return upstream to the obstacle when the coast is clear.

This paper hypothesizes that the two weirs in China Lake Stream may have been built and operated together to act as a fish trap. If this is true, the trap would have been operated in the following manner. In the spring of each year, as run-off began to subside, saplings were inserted vertically into the stone foundations of the weirs and interlaced horizontally with brush to create a barrier across the stream channel. A narrow chute was left open on the lower weir. As alewives began to migrate up the stream they passed through this chute in the lower weir but their progress was stopped by the impassable upper weir. Over a period of several days, the river channel between the two weirs filled with alewives.

Once the channel was deemed full enough of alewives to make harvesting easy, the lower chute was closed off to prevent alewives from escaping downstream. Then, members of the family group (or groups) waded into the stream channel with baskets and/or nets and easily captured the alewives which could not swim upstream or downstream to escape. Once the number of alewives left in the stream was reduced by the harvest, the barrier at the lower weir was removed to let more alewives upstream into the "trap" until the numbers were again high enough to allow for easy capture. This "refilling of the trap" might have been done several times a day during the height of the run or every few days at the beginning or the end of the run. This method would also allow the group sufficient time to stake and smoke the alewives they had already caught, while letting new migrants to collect in the trap.

This same method and sequence of weirs would be equally effective in capturing adult American eels migrating out of China Lake through China Lake Stream during the fall because it would greatly increase the effectiveness of a spearing or netting/basket harvesting.
A "W" shaped stone fishing weir for alewives, West Branch Sebasticook River, Pittsfield, Maine. First identified by Tim Watts and the author in fall 2002.

Tthe China Lake Stream weirs and the West Branch Sebasticook weir in the town of Pittsfield shows a key design difference. The China Lake Stream weirs lack any inverted "V" pointing upstream, and instead are straight-line structures perpendicular to the stream flow. A possible clue is that the river channel at the West Branch Sebasticook site more than 100 feet wide: twice as wide as the China Lake Stream sites. A straight line weir at the West Branch Sebasticook site would be far less effective as a "W" shaped weir at concentrating alewives in a small, confined area in a wide stream channel. On the other hand, the much narrower stream channel at the China Lake Stream site would have made a "V" design unecessary, because the large number of alewives coming up China Lake Stream would have easily filled the narrow channel from bank to bank.

China Lake Stream: A Regional Fishing Center?

The sheer quantity of alewives that could be easily and quickly caught at the weirs at China Lake Stream (hundreds of thousands) would have greatly exceeded the number that could be preserved by a small family group or groups, as would the number of alewives needed to support them. The extensive prehistoric habitation areas along the Sebasticook River near the mouth of China Lake Stream, and the role of the Sebasticook as a highly used east-west travel corridor by Indians as late as the 1700s (hence the construction of Fort Halifax in 1754 to block communication between the Kennebec and Penobscot tribes), suggest the China Lake Stream weir site may have served as a regional fishing center. This is suggested by a document at the Taunton, Mass. Historical Society containing a 1600s account of the regional use of an alewife fishing site at the mouth of the Cohannet River (Mill River) in what is now Taunton, Massachusetts:

"The ancient standers remember that hundreds of Indians would come from Mount Hope and other places every year in April, with great dancings and shoutings to catch fish at Cohannit and set up theyr tents about that place until the season for catching alewives was past and would load their backs with burdens of fish & load ye canoes to carry home for their supply for the rest of the year and a great part of the support of ye natives was from the alewives."

This document further describes the intensive use of alewives by the earliest settlers as fertilizer for corn and the use of children to catch them:

"The first English planters in Taunton found great relief from this sort of fish, both for food & raysing of corne and prized them so highly that they took care that when Goodman Linkon first craved leave to set up a grist mill at that place, a town vote should be passed that the fish should not be stopped. It is well known how much other Towns are advantaged by this sort of fish. Middleboro will not permit any dam for any sort of mills to be made across their river to stop the course of fish nor would they part with the privilege of the fish if any would give them a thousand pounds and wonder at ye neighboring town of Taunton, that suffer themselves to be deprived of so great a privilege ....

"These fish may be catcht by the hands of children in theyr nets while the parents have y'r hands full of work in the busy time of Spring to prepare for planting. Some of Taunton have been forced to buy Indian corn every year since the fish were stopped, who while they fisht, they'r ground used to have plenty of corne for y'r family & some to spare to others. The cry of the poor every year for want of the fish in Taunton is enough to move the bowels of compassion in any man, that hath not an heart of stone."


There are many reasons why this hypothesized two-weir harvesting technique may never have occurred at this site on China Lake Stream. It is possible that the two instream structures found were never built or used as fish weirs; that only one was built as a fish weir; that both structures were fish weirs but were built and operated centuries or millennia apart.

A key factor confounding the truth or falsity of this hypothesis is that there is an extreme paucity of information about any prehistoric fish weirs in streams in the northeast United States. Confirmed prehistoric weir sites and structures in Northeast rivers are extremely rare; and there are almost no eyewitness accounts from European during the Contact Period which describe how these structures were actually used and operated by native people to catch migratory fish such as alewives and eels, which were undoubtedly the target species in China Lake Stream.

With these caveats in mind, a number of evidentiary points suggest this "two weir" fish trap method may have been widely used by prehistoric peoples. The first point is that the general strategy has been widely employed for centuries. The general strategy is that fish are guided into a constricted and confined area in which passive obstructions and barriers are placed to hinder their escape. This is basic principle of the common type of lobster traps and minnow traps sold and used in coastal areas today. This is also the fundamental design principle of "fyke nets" used today to catch juvenile eels in Maine rivers and the many varieties of brush and stick weirs (later equipped with netting) that formed the basis of the enormous weir fisheries for salmon, striped bass, alewives and shad in the tidal estuaries of New England rivers in the 19th century, particularly in the Kennebec, Androscoggin and Penobscot. Baum (1997) reproduces diagrams of many of these weirs, which all use the same design and strategy of that hypothesized for the two adjacent stone weir structures on China Lake Stream, ie. to guide the fish into the "trap" and then hinder their escape with passive barriers.

Future Research Needs:

Due to the advanced age of prehistoric stone weirs, the existence of dam impoundments that flood and obscure them, the cultural overprint of 18th, 19th and 20th century mill dams built at or near the same sites, the effectiveness of stream flow and floods over centuries at destroying or obscuring their remnants, the lack of any focussed effort to locate them, and the skill and intuition necessary to even notice them, it is not surprising that there is virtually no information on the location and types of prehistoric fish weirs in New England and the northeast United States.

The discovery of these two conjectured prehistoric stone weirs at China Lake Stream was only possible due to the very recent (2008) removal of a large hydroelectric dam that had been in place for a century and a directed reconnaissance search by the author on the restored stream reach which specifically focussed on identifying any remnants of a prehistoric weir. This search was driven by the previous historic and biological research which showed that:

a) China Lake Stream once supported large numbers of migratory fish that were actively sought by prehistoric peoples in the area;
b) Extensive archaeological evidence of dense prehistoric habitation along the Kennebec, Sebasticook and China Lake Stream riparian corridors;
c) The 2002 discovery by Tim Watts and the author of a large, prehistoric "W" shaped stone fishing weir on the West Branch Sebasticook River in Pittsfield, Maine and the early 1990s discovery of a wooden stake weir in Sebasticook Lake, Newport, Maine dated to 5,700 B.P.

A key support for the "two weir fish trap" hypothesis presented here would be the identification of multiple sites in the Northeast that fit the general physical description of the China Lake Stream site described herein. If nothing else, this hypothesis has value in alerting investigators to always look for a second weir site just above or below one that has been tentatively identified.

The weir site and adjacent shoreline areas described above would benefit from a professional archaeological survey to determine the full extent of prehistoric use and habitation.

Baum, E.T. 1997. Maine Atlantic Salmon: A National Treasure. Atlantic Salmon Unlimited. Hermon, Maine.
Doyle, R.G. 2008. Identification of Lithic Artifacts from Central Maine Coastal Archaeological Sites: A Case Study in Regional Lithic Acquisition Strategies. Flying Passage Press. Gardiner, Maine.
Hanson, J.W. 1852. History of Gardiner and Pittston. William Palmer, Publisher. Gardiner, Maine.
Josselyn, John. 1674. John Josellyn, Colonial Traveler. A Critical Edition of Two Travels to New England. Paul J. Lindholt, editor. University Press of New England. 1988.
Pory, John. 1622. Letter of John Pory to the Earl of Southhampton. In: Three Visitors to Early Plymouth. Reprinted by Plimoth Plantation. Plymouth, Mass.
Watts, D.H. 2004. Maine Historic Engineering Record. Dam Number Five, Cobbosseecontee Stream, Gardiner, Maine. MHER No. 22. Prepared for the Maine Historic Preservation Commission. Augusta, Maine. PDF here.
Watts, D.H. 2003. A Documentary History of the Alewife (Alosa pseudoharengus) in Maine and New England. Friends of the Kennebec Salmon. Augusta, Maine. PDF here.