Monday, November 30, 2009

New Evidence Doubles Natural Range of Striped Bass in Kennebec River, Maine.

By Douglas Watts
Augusta, Maine
November, 2009

Conventional wisdom holds that striped bass (Morone saxatilis) did not migrate up the Kennebec River past Ticonic Falls at Waterville, Maine, 20 miles above the river's head of tide in Augusta, Maine.

Archaeological evidence suggests this may be wrong. Arthur Spiess, chief archaeologist with the Maine Historic Preservation ResearchBlogging.orgCommission, has gone through his research holdings and located a record of striped bass vertebra found in a recent excavation of a food cache at the late 1600s Kennebec Indian village at the junction of the Sandy and Kennebec Rivers in Norridgewock, Maine. The vertebra is in sufficiently good preservation to provide a positive identification to species (Spiess 2009, personal communication).

This finding expands upon recent archaeological research showing striped bass lived throughout the Sebasticook River drainage prior to 18th and 19th century dam building; and recent historic research on Maine's Penobscot River showing that large striped bass (20-40 pounds) migrated much farther up the Penobscot than previously thought.

Norridgewock is at the junction of the Kennebec and Sandy Rivers, approx. 30 river miles above Ticonic Falls at Waterville and 10 miles above the large natural falls at Skowhegan.


Historic records and oral recollections, collected and summarized in Atkins (1867), show that alewives and shad migrated past Ticonic Falls on the Kennebec as far as the junction of the Kennebec and Sandy Rivers in Norridgewock. Atkins states that alewives and shad could not ascend the Kennebec past a one mile series of falls and rapids just above Norridgewock, at Madison and Anson, Maine. Above these falls at Madison, Atkins found no records or recollection of alewives and shad, but found numerous records of Atlantic salmon. As for striped bass, Atkins states they "ascended as far as Waterville, and to some distance on the Sebasticook."

[Here is a movie snippet of Ticonic Falls in Waterville.]

Swum or Carried?

The use of archaeological digs to determine the natural range of a fish carries an obvious uncertainty. Was the fish caught somewhere else and carried to the site and eaten? Or was the fish caught at the site and eaten?

In some cases the distinction is easy. If the fish is a saltwater-only species, ie. a swordfish or mackerel, and is found 100 miles away from saltwater, we can conclude it had to have been brought there. With striped bass, the distinction is not so easy. The striper in question could have been caught miles away and carried to the site, or it could have been caught in the Kennebec River right next to the site in Norridgewock and consumed a few hours after being caught.

Norridgewock is about 30 river miles from Ticonic Falls in Waterville, where we know stripers live (since we see them and catch them). Dams prevent stripers from getting any farther up river. If the natural limit of stripers was at Ticonic Falls, then the striper eaten at Norridgewock would have to have been caught at or below Waterville and then transported 30 miles upriver to Norridgewock.

By canoe, the upriver 30 mile trip from below Waterville to Norridgewock would take at least several days. Even a downstream canoe trip on the Kennebec only covers about 15-20 miles a day. Paddling against the current would at least halve this. If we assume 10 miles a day upstream by a very strong paddler, the trip from Waterville to Norridgewock would take three days. A striped bass transported this distance would be seriously decayed and inedible if left out dead for three days at "room temperature." It would be .. err... ripe. This makes it hard to imagine how a striper could have been caught below Waterville and brought to Norridgewock to be eaten there.

The next question is whether the striped bass found at Norridgewock could have been caught and preserved by smoking or salting well down river and then brought up river. Native Americans smoked fish to preserve them, particularly alewives and shad. Striped bass can be smoked, so it is at least possible the striper in question at Norridgewock was caught well down river smoked and brought up to Norridgewock where it was eaten and its bones were discarded.

Now let's look at other reasons why or why not this striper might have been caught at Norridgewock.

How far do striped bass migrate up New England rivers?

The short answer seems to be as far as they can, especially if there are large runs of alewives and shad and eels to feed on. The only thing which seems to prevent the upstream migration of striped bass on large rivers are impassable falls, or in this era, impassable dams.

The conventional wisdom on the Kennebec River is that Ticonic Falls in Waterville was, for striped bass, an impassable falls. We have no evidence to prove this. All we have is a brief statement by Atkins (1867) that striped bass did not migrate above the falls. Because the falls have been dammed since the early 1800s, there is no way to determine today if striped bass would migrate above the falls if they were in their natural condition and not dammed.

We know from Atkins that alewives and shad migrated well above Ticonic Falls, all the way to Norridgewock, 30 miles farther upriver. We know that striped bass follow alewife and shad migrations up river to eat them. Given these facts, there would be a definite reward for stripers to continue migrating upriver past Ticonic Falls to feed on alewife and shad. The question then becomes if the physiology of striped bass prevents them from ascending falls that alewives and shad can pass.

Alewives and shad migrate falls by swimming through them, unlike Atlantic salmon, which can leap out of the water to get over falls that are too steep to swim through. Alewives and shad do this by finding the most effective passage route and using what is called "burst swimming" to get through small areas with very high current velocities, ie. at the lip of a falls. Burst swimming is an extremely energetic swimming motion that fish can only sustain for a short period of time. Is there any evidence that striped bass lack the "burst swimming" ability of alewives and shad?

What is the swimming speed of a fully laden Kennebec River striped bass?

Research by Castro-Santos et al. (2005) shows a clear difference in the response of clupeids (alewives, blueback herring and shad) vs. striped bass, walleye and white sucker to a high velocity challenge in experimental flumes. But the authors note, "The consistent failure by the nonclupeids to switch to the distance-maximizing groundspeed for sprint mode means that these species are less likely to successfully traverse velocity barriers, even though such success is within their physiological capacity."

This finding suggests that nothing in the physiology of striped bass prevents similarly sized striped bass from ascending the type of velocity barriers ascended by alewives and shad. Instead, their reluctance (when they exhibit it) seems more likely behavioral. Unlike shad and alewife, the upstream migrations of striped bass well above the head of tide are driven by feeding, not spawning, especially for stripers which have yet to reach sexual maturity. Striped bass do not have the sexual/survival imperative to migrate far upstream that alewives and shad possess during their upstream migrations.

It's a lot more important for alewives and shad to get past difficult instream obstacles, and it's less important for striped bass, and for this reason, alewives and shad seem to have an instinctive tendency to devote far more time and energy to ascending an obstacle than striped bass of similar size.

The experimental observations of Castro-Santos et al. suggest striped bass will only ascend difficult falls opportunistically and will only devote a discrete amount of time and effort to do so. If water and flow conditions are conducive to passage, X number of stripers below a falls will find successful passage routes, ascend the falls, and follow the migration of alewives and shad and feed on them. If and when flow conditions at a falls make passage very difficult, fewer stripers will decide to invest in the effort and fewer will pass over.

This reasoning is supported by the fact that the post-spawning mortality rate of alewives, blueback herring and shad is in the range of 50 percent in New England river systems. This mortality is in part due to these fish becoming so physically exhausted, battered and withered during their spawning migrations that they do not survive after spawning to return to the ocean. From a genetic sense, it is worth it for a sexually mature alewife or shad to exert tremendous energy to reach ideal spawning habitat, even if this expenditure greatly reduces their chances of surviving after spawning.

The act of trying to swim over a difficult falls places a fish in great risk of being caught and eaten or injured by fish-eating birds such as great blue heron, cormorants, osprey and bald eagle, as well as mink, otter, black bear and seals, which patrol and set up feeding stations at these sites. Unlike alewives and shad, striped bass have much less at stake in getting above these falls, and appear less willing to accept the level of risk that alewives and shad accept at the same site. [Footnote: Since the Edwards Dam was removed in Augusta in 1999, harbor seals have been repeatedly observed at Ticonic Falls in Waterville during alewife and shad runs; 18th century records describe black bear catching alewives from Worromontogus Stream, which enters the Kennebec in Gardiner, Maine.]

From this evidence it seems implausible to discount the opportunistic migration of striped bass at the same sites where alewives and shad are documented to pass because there is no evidence that striped bass are physiologically less able than alewives and shad to swim past the same instream obstacles.

How big are Ticonic Falls?

Ticonic Falls is in downtown Waterville and Winslow, Maine. Like most "falls" on New England coastal rivers, they are not actual waterfalls, but a river section that flows over bare bedrock, creating turbulent rapids. The dam at Ticonic Falls is of mid-19th century construction and on the falls itself consists of a poured concrete wall anchored in the ledges. This wall is anywhere from 6 to 10 feet higher than the natural ledge and creates a 1 mile long impoundment of what was naturally a long section of rapids called "College Rips." The concrete wall/spillway appears to be built at the top lip of the falls. For this reason, much of the original falls are still in their natural condition, and at low river flows one can walk all around them and examine them in detail. I have done this for many years to study exactly how fish get up the falls to the toe of the concrete spillway, where their progress, unfortunately, is completely stopped.

What I found is that virtually every diadromous fish native to the river are able to swim all the way through the falls to the toe of the concrete spillway, including alewife, blueback herring, stripers, sea lamprey, juvenile American eel as well as exotic species such as small brown trout and smallmouth bass. Investigations conducted since 1999 by the dam owner, FPL Energy, during flashboard replacement at the spillway in late spring, have found adult shortnosed sturgeon and Atlantic salmon at the toe of the spillway as well. Because the toe of the concrete spillway is built on the surface of the natural ledges, this suggests that if the concrete spillway were not present, all of these species would be able to swim over the ledges and continue upstream.

This raises the question of why Atkins suggested Ticonic Falls as the natural upstream migration limit for striped bass on the Kennebec River. Atkins wrote this in 1867, or 30 years after all fish migration up the Kennebec River had been stopped by construction of the Edwards Dam in Augusta. Atkins was unable to observe any migratory fish in the Kennebec River above Augusta during his lifetime. Instead, he was forced to rely on scattered written records and the 30-50 year old oral recollections of people who knew the river before it was dammed in 1837. By Atkins' time, these people were getting hard to find. Atkins' statement that stripers "ascended as far as Waterville" suggests he could not find any records or observations of striped bass above Waterville and decided to phrase his range description. His method can be seen in the way he described stripers as going "to some distance" up the Sebasticook in his original 1867 report, but in his 1869 report changed this to say stripers went a "short distance" up the Sebasticook. This editing suggests Atkins preferred to underestimate the natural, pre-dam range of fish species in the Kennebec River unless he had compelling evidence to suggest otherwise. This preference by Atkins is important, since his work has become virtually the sole basis for all modern estimates of the natural range of diadromous fish in the Kennebec and other Maine rivers. [Footnote: Recent documentary research at the Maine State Archives and Maine State Library shows Atkins missed a large number of historic records from the late 1700s and early 1800s when he published his 1867 and 1869 reports. These records were available to Atkins at the time, but for unknown reasons he did not use them.]

Different migration windows

The upstream migration of clupeids in river systems are determined by the timing of their sexual clocks. Each species, alewife, blueback herring, and American shad have a finite and limited migration window in which they must successfully negotiate instream obstacles in a river to get to their natal spawning habitat.

On the Kennebec at Waterville, the migration window for alewives is late April to late May, and for blueback herring and shad the window is from mid May to mid June. To reach preferred spawning habitat before their sexual organs "command" them to spawn, all three species must negotiate the river on a narrow and circumscribed schedule of 4-6 weeks.

In contrast, striped bass migrating upriver solely for feeding purposes have sexual constraints on their migration window. Unlike spawning clupeids, if flow conditions at a falls are not conducive to passage until early or mid summer, the stripers can wait. The reward for waiting for a passage opportunity at a falls is that the stripers gain access to an enormous amount of riverine habitat for feeding that is comparatively empty of competing predators. The stripers that pursue and succeed in the opportunity to get over falls get to go to the "top of the feed line." On the Kennebec, a striper patient and strong enough to pass over Ticonic Falls gains access to miles and miles of ideal habitat in the middle portions of the Kennebec and Sandy Rivers which is comparatively barren of competing predators but is full of juvenile alewives, blueback herring, shad and eels. The growth and survival advantage for striped bass who select this option cannot be discounted.

Implications for restoration of striped bass

The Kennebec River is one of the few large river systems north of the Hudson which had a native, spawning population of striped bass (Atkins 1869; Squiers 1988; Dadswell 1996). The presence of native striped bass in the Kennebec River is due to the lack of impassable falls above tidewater. This allows sexually mature stripers to swim far enough up river so their free-floating eggs can hatch before encountering waters with a salinity in excess of 1 ppt.

Dam-building on the Kennebec River after 1837 severely constrained the ability of native striped bass to move far enough upstream to successfully spawn. Removal of the Edwards Dam at the Kennebec's head of tide in 1999 has restored access for striped bass to 20 miles of above-tidal river habitat between Augusta and Waterville, Maine. Removal of the Fort Halifax Dam at the mouth of the Sebasticook River in Winslow, Maine in 2008 has created the potential for restoring access for striped bass to its native habitat in the vast 1,000 square mile Sebasticook River drainage, the Kennebec's largest tributary.

Impassable dams still prevent striped bass from freely ascending the Kennebec past Waterville and the Sebasticook past Benton Falls, six miles from its mouth. Regulatory decisions on whether to allow striped bass to migrate upriver past these dams have been solely based on historic records gathered by Atkins (1867). Archaeological evidence from both rivers shows that striped bass migrated up the Kennebec and Sebasticook Rivers much farther than contemplated by Atkins, greatly increasing the natural, historic range of striped bass in the Kennebec River system compared to what has been previously assumed. Based upon this new evidence, fisheries agencies in Maine should ensure that any striped bass attempting to enter fishlifts at the Lockwood Dam on the Kennebec River in Waterville and at the Benton Falls Dam on the Sebasticook River are safely passed upriver into their native habitat upstream.

This new evidence shows the need for fisheries scientists to work closely with archaeologists to factually establish the natural range of diadromous fish species in river systems, especially those heavily impacted by damming in the 18th and 19th centuries. Like all New England rivers, the Kennebec was heavily dammed beginning in the early 19th century and for this reason, delineation of the natural range of diadromous species in these river systems must be pieced together through obscure and fragmentary documentary sources. Archaeological evidence provides a critical ground truthing to assess the veracity of later records which rely upon secondary historic sources. To gain access to the archaeological record, fisheries scientists must get to know archaeologists working in the same watershed and ask what they know and what they have found. Often, as in this case, a detail considered very minor to archaeologists (a striped bass bone from the 1600s in Norridgewock, Maine) can be valuable evidence for a fisheries scientist trying to piece together the natural range and habitat of diadromous fish species and the pre-industrial ecology of northeast coastal river systems.
References:

Atkins, C. 1867. Maine Fish Commissioners Report in Twelfth Annual Report of the Secretary of the Maine Board of Agriculture. Stevens & Sayward. Augusta, Maine.

Castro-Santos, T. 2005. Optimal swim speeds for traversing velocity barriers: an analysis of volitional high-speed swimming behavior of migratory fishes. Journal of Experimental Biology, 208 (3), 421-432 DOI: 10.1242/jeb.01380

Dadswell, M.J. 1996. The Removal of Edwards Dam, Kennebec River, Maine. Its Effect on the Restoration of Anadromous Fishes. Prepared for the Kennebec Coalition. Augusta, Maine. March, 1996.

Squiers, T. 1988. Anadromous Fisheries in the Kennebec River Estuary. Maine Department of Marine Resources. Augusta, Maine.

Spiess, Arthur. 2009. Unpublished archaeological records from the database of the Maine Historical Preservation Commission, Augusta, Maine.

4 comments:

Anonymous said...
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Unknown said...

The dams which exist will still prevent successful spawn due to their reduction of water velocity upstream. Since the semi-buoyant striped bass eggs require a minimal flow to prevent settling on the bottom, merely lifting them above these existing dams won't increase their spawning success. If the dams aren't removed completely and the rivers returned to their wild nature, I'm afraid successful striped bass spawn in this section of water will only be a happy thought. Shawn McNew

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