Sea Lamprey Control in Lake Champlain

J. Great Lakes Res. 29 (Supplement 1):655–676 Internat. Assoc. Great Lakes Res., 2003

Sea Lamprey Control in Lake Champlain J. Ellen Marsden1,*, Brian D. Chipman2, Lawrence J. Nashett3, Jon K. Anderson2, Wayne Bouffard4, Lance Durfey3, John E. Gersmehl4,5, William F. Schoch3, Nicholas R. Staats4, and Adam Zerrenner1,6 1School

of Natural Resources Aiken Center, University of Vermont Burlington, Vermont 05401 2Vermont

Department of Fish and Wildlife 111 West Street Essex Junction, Vermont 05452

3New

York State Department of Environmental Conservation Bureau of Fisheries Route 86, P.O. Box 296 Ray Brook, New York 12977-0296 4U.S.

Fish and Wildlife Service Lake Champlain Fish and Wildlife Resources Office 11 Lincoln Street Essex Junction, Vermont 05452 ABSTRACT. In 1990, the United States Fish and Wildlife Service (USFWS) and state agencies initiated an 8-year experimental sea lamprey (Petromyzon marinus) control program on Lake Champlain to reduce parasitic phase sea lamprey and increase sport fish survival and growth. Twenty-four 3-trifluoromethyl-4-nitrophenol (TFM) treatments were conducted on 13 tributary systems, and nine Bayluscide treatments were conducted on five deltas. Most tributaries received two rounds of treatment, 4 years apart. Trap catches of spawning-phase sea lamprey in three monitored tributaries declined by 80–90% from 1989 to 1997, but nest counts were reduced by only 57% during the same period. Sixteen of 24 TFM treatments reduced ammocoetes to less than 10% of pre-treatment levels. Eight of nine Bayluscide treatments resulted in mean ammocoete mortality rates over 85% in caged test animals. Nontarget effects were noted among amphibians, mollusks, macroinvertebrates, native lamprey, and other fishes, and were higher for Bayluscide treatments than TFM. Recovery of delta taxa occurred within 4 years after treatment. Wounding rates on lake trout and Atlantic salmon were reduced in the Main Lake basin. Catches-per-unit-effort (CPUE) and estimated angler catch of lake trout increased. A moderate (25%), statistically significant increase in survival of 3–4 yr lake trout was noted. Returns of Atlantic salmon (Salmo salar) to tributaries increased significantly after treatment, and there was an estimated 3-fold increase in returns to the Main Lake sport fishery. Angler catches of brown (Salmo trutta) and rainbow trout (Oncorhynchus mykiss) were higher in 1997 than in 1990. Economic analysis of the program indicated a 3.5:1 economic benefit: cost ratio. Results indicate that the experimental control program was successful, and provide justification for continuing sea lamprey control on Lake Champlain. INDEX WORDS:

Sea lamprey, control, TFM, Bayluscide, economic analysis, Lake Champlain.

*Corresponding author. E-mail: [email protected] 5Current address: 267 Belair Dr., Colchester, Vermont 05446 6Current address: Sacramento Fish and Wildlife Office, U.S. Fish and Wildlife Service, 2800 Cottage Way, Suite W-2605, Sacramento, California 95825

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INTRODUCTION Sea lamprey (Petromyzon marinus) control in the Laurentian lakes was most recently initiated in Lake Champlain. In common with most of the Great Lakes, native salmonid populations (lake trout Salvelinus namaycush and landlocked Atlantic salmon Salmo salar) in Lake Champlain have been extirpated. These species are now supported by stocking, though limited natural reproduction by both species has been documented. A fishery for two exotic salmonids, rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta), was established in the mid 1970s and is also supported by stocking. Lamprey control was judged to be necessary to achieve fisheries management objectives and improve the economic benefits from sport fishing. An experimental sea lamprey control program (ESLCP) was initiated in 1990 to reduce parasitic phase sea lamprey abundance, assess effects of the reduction on the sport fishery and economics of the region, and to facilitate formulation of long-range policies and management strategies. This paper documents the results of the control program, the current status of sea lamprey in Lake Champlain, and discusses options for future control. LAKE CHAMPLAIN Lake Champlain is a long, narrow lake, approximately 200 km long and 21 km wide with an area of 1,130 km2, that lies between New York and Vermont and extends northward into Quebec (Fig. 1). The fish fauna is similar to that of the Great Lakes: coregonid species are limited to lake whitefish (Coregonus clupeaformis) and lake herring (C. artedi), and major forage for piscivores are native rainbow smelt (Osmerus mordax) and yellow perch (Perca flavescens). The predator population is dominated by the four salmonids and walleye (Stizostedion vitreum). Historic commercial fishing for lake trout was limited, and there is currently no traditional commercial fishery on the lake. The origin of sea lamprey in Lake Champlain has long been a topic of debate. A number of researchers, most recently Lawrie (1970) and Daniels (2001), suggest that sea lamprey are native to Lake Ontario, the Finger Lakes, and Lake Champlain, based largely on the absence of effective barriers to block their migration into these lakes. Sea lamprey could have gained access to the lake from the St. Lawrence River via the Richelieu River, or may have entered more recently from the Hudson River via the Champlain Canal, opened in 1823, or from

FIG. 1. The Lake Champlain drainage basin, showing lake basins, lake management zones, and tributaries mentioned in the text. Tributaries that were treated with TFM are underlined; deltas treated with Bayluscide are indicated by small triangles.

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the Richelieu River via the Chambly Canal, opened in 1843 (Lawrie 1970, Smith 1972). The first records of lamprey in the lake date from 1841 (Halnon 1963), but the species identity is uncertain; a later survey of fish species in Lake Champlain in 1894 did not include sea lamprey, but by 1929 they were reported to be moderately common (Evermann and Kendal 1902, Greeley 1930). SALMONIDS IN LAKE CHAMPLAIN It is uncertain whether sea lamprey were a factor in the decline of lake trout and Atlantic salmon populations in Lake Champlain. Both species were over-harvested during the 1800s, and Atlantic salmon reproduction was adversely affected by construction of dams (Plosila and Anderson 1985). Lake trout populations were considered to be extinct by the late 1800s. No lake trout were found in lakewide surveys in 1928 and 1953–4 (Anderson 1978). Early stocking attempts were made in 1894–1896, and again in 1958 and for several years thereafter, but these efforts failed to produce a population of lake trout in the lake (Halnon 1963). A coordinated stocking program began in 1973. Strain composition and ages of stocked lake trout were standardized with the 1988 year class and focused on yearlings, primarily from Seneca Lake strain and egg take from feral Lake Champlain lake trout. Lake trout are stocked annually in the Main Lake only; limited stocking occurred in 1972 and 1975–1977 in Malletts Bay and the Inland Sea, but was discontinued due to poor catches of adults. Between 39,000 and 341,000 lake trout have been stocked annually since 1973 (Fig. 2). Sporadic Atlantic stocking began in 1962 (unpubl. data). Stocking of rainbow trout began in 1972, and of brown trout in 1977 (Fisheries Technical Committee 1999). With the implementation of sea lamprey control, total annual stocking of all species combined was limited initially to 690,000 yearling equivalents lakewide. Managers were concerned that increased survival and growth of lake trout as a result of sea lamprey control would lead to increased predation on rainbow smelt, potentially causing a decline in the primary salmonid forage base (LaBar 1993). Accordingly, the total number of all salmonids stocked each year was reduced by up to 24% beginning with the 1994 year-class. This reduction did not affect evaluation of the ESLCP because fish stocked at reduced numbers (primarily lake trout) were not recruited into the sport fishery or sampling gear prior to the end of the evaluation period.

FIG. 2. Numbers of yearling-equivalent lake trout stocked into Lake Champlain by year class and strain, 1972–1997. “Finger Lakes” represents Seneca Lake strain, and also includes composite strains of progeny from feral lake trout in lakes Ontario and Champlain, which were assumed to be largely of Seneca Lake origin. “Other strains” include Jenny Lake, Lake Michigan, Lake Superior (Marquette), Manitoba (Clearwater), Adirondack (Raquette Lake, Lake George), and Maine (Allagash Lake).

Experimental Sea Lamprey Control Program Joint efforts to restore fisheries in Lake Champlain began in 1973 with the formation of the Lake Champlain Fish and Wildlife Management Cooperative (“Cooperative” herein), composed of the U. S. Fish and Wildlife Service (USFWS), Vermont Department of Fish and Wildlife (VTDFW), and the New York State Department of Environmental Conservation (NYSDEC). The Cooperative developed A Strategic Plan for the Development of Salmonid Fisheries in Lake Champlain in 1977 (Fisheries Technical Committee 1977), with specific, measurable objectives to re-establish a lake trout and Atlantic salmon fishery, establish a rainbow trout fishery, and maintain the existing harvest of rainbow smelt. It became apparent that sea lamprey control would be needed in order to achieve these objectives (Gersmehl and Baren 1985, Plosila and Anderson 1985). For example, summer gillnetting data revealed a wounding rate (type AI–AIII wounds) for lake trout > 635 mm in the Main Lake (zones 3A-3C) that varied from 87 to 100%, with a mean number of up to 11 attack marks per lake trout > 635 mm prior to control. The Cooperative initiated an eight-year experi-

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mental program of sea lamprey control in 1990. The program was based heavily on the use of two chemical lampricides, 3-trifluoromethyl-4-nitrophenol (TFM) and Bayluscide 5% granular (Bayluscide). Evaluation of the program’s success was based on 30 criteria relating to sea lamprey reduction, sport fishery response, and forage fish assessment (Engstrom-Heg et al. 1990, Fisheries Technical Committee 1999). Use of federal funding for the ESLCP required the preparation of an Environmental Impact Statement (EIS) and the appropriate public processes associated with the National Environmental Policy Act (NEPA). Permits for sea lamprey control were obtained from both states. State-listed endangered and threatened species addressed by these permits included species which could potentially be threatened by lampricide treatments in certain streams, such as northern brook lamprey (Ichthyomyzon fossor—endangered in Vermont), American brook lamprey (Lampetra appendix—threatened in Vermont), lake sturgeon (Acipenser fulvescens— endangered in Vermont), eastern sand darter (Ammocrypta pellucida—threatened in New York and Vermont), channel darter (Percina copelandi)– proposed for listing as endangered in Vermont), and six unionid mussel species listed as threatened or endangered, or proposed for listing in Vermont. The species proposed for listing in Vermont during the ESLCP are now officially listed. Pre-control Assessment of Sea Lamprey Prior to initiation of the ESLCP on Lake Champlain, an assessment of sea lamprey distribution was conducted to locate and prioritize streams for treatment and to provide data for evaluating success of the control program (Gersmehl and Baren 1985). Thirteen sea lamprey producing tributary systems and five deltas were given priority for treatment based on ammocoete catch-per-unit-effort (CPUE) in streams sampled with electrofishing gear and ammocoete density on deltas sampled with Bayluscide (Fig. 1). The Poultney River and its tributary, the Hubbardton River, were treated and assessed as separate streams, so results from the two rivers will be reported separately here. Five additional stream systems which contained sea lamprey were not designated for treatment due either to low ammocoete densities (Youngman Brook, Winooski River/ Sunderland Brook, Missisquoi River), or presence of northern brook lamprey (Malletts Brook/Indian Brook). The Pike River/Morpion Stream system

was not treated because water quality at the time may have resulted in an unacceptably high non-target fish kill, and uncertainty regarding apparent contribution of these streams to the parasitic phase population did not warrant pursuit of international permitting for the purposes of the ESLCP. Seventeen additional tributaries were surveyed using electrofishing or Bayluscide and did not contain sea lamprey; additional tributaries in the Lake Champlain basin were classified as unsuitable for sea lamprey and were not surveyed. Control Methods TFM Two rounds of treatments were scheduled for each of the 13 tributary systems with a 4-year interval between treatments (Table 1). Second treatments of Stone Bridge Brook and Beaver Brook were not needed due to absence of sea lamprey or low sea lamprey recolonization. The first (1991) treatment of Trout Brook was canceled because permit conditions regarding the capture and holding of American brook lamprey outside of the treated reach could not be met. A decision not to treat the Saranac River in 1996 was made due to flood-related scouring that reduced ammocoete habitat, and to the low estimated kill that occurred during the first treatment and high costs associated with treating the river. Generally, TFM dosages used in New York were based upon a minimum lethal concentration (MLC) established by on-site toxicity test, multiplied by a factor of 1.5 or lower. In Vermont, dosage was based on the lower of the MLC values determined by toxicity test, or using prediction charts, based on pH and alkalinity and multiplied by similar factors (Bills et al. 2003). The duration of primary applications was usually 12 hours in streams in both states. Bayluscide Bayluscide (5% granular) formulation, applied at a rate of 100 pounds per acre, was utilized for limited larval surveys in estuarine and lentic environments and for the treatment of deltas on the New York side of the lake (Table 1). Similar surveys indicated that sea lamprey were not present in delta areas of Vermont tributaries. Five deltas were treated in 1991, and four of these were treated again in 1995. The Little Ausable River delta did not receive a second treatment in 1995 due to a lack of recolonization.

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TABLE 1. Schedule of TFM and Bayluscide treatments of tributary streams and deltas in the Lake Champlain basin, with stream discharge data (m3/sec), length (km) or surface area (ha) of treatment, and amount of active ingredient of each chemical used. Stream discharge data were measured during TFM treatments. TFM and Bayluscide are reported as kg of active ingredient.

TFM Boquet R., NY Little Ausable R., NY Ausable R., NY Salmon R., NY Beaver Br., NY Putnam Cr., NY Lewis Cr., VT Stone Bridge Br., VT Mount Hope Br., NY Trout Br., VT Poultney R., VT/NY Hubbarton R., VT* Saranac R., NY Great Chazy R., NY Bayluscide Boquet R. delta, NY

Years treated

Discharge (m3/sec)

Km/area (ha) treated

TFM (kg)

1990 1994 1990 1994 1990 1994 1990 1994 1990 1990 1994 1990 1994 1991 1991 1995 1995 1992 1996 1992 1996 1992 1992 1996

4.81 1.98 0.48 0.42 7.50 9.20 0.71 0.42 0.03 0.42 0.17 0.96 0.59 0.04 0.20 0.07 0.02 4.81 4.25 0.54 0.57 9.62 1.13 3.28

4.2 4.2 9.8 9.8 10.5a 10.5a 6.4 6.4 1.6 7.7 7.7 15.1 8.4 4.7 2.1 2.1 0.6 16.9 16.9 3.2 0.6 5.3 33.1 33.1

380 255 100 125 560 578 120 70 6 98 99 345 150 28 30 17 5 360 542 70 75 811 386 768

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

—

85.0 85.0 21.9 66.8 73.7 21.9 21.9 62.4 55.5

0 0 0 0 0 0 0 0 0

477 477 123 375 414 123 123 350 311

1991 1995 Little Ausable R. delta, NY 1991 Ausable R. delta, NY 1991 1995 Salmon R. delta, NY 1991 1995 Saranac R. delta, NY 1991 1995 aincludes 0.8 km of tributary Dry Mill Brook. *tributary to Poultney River

— — — —

Barriers Prior to the ESLCP, preliminary studies to examine the feasibility of lamprey barriers were conducted on 15 rivers (Anderson et al. 1985). The authors concluded that it may be feasible to design and construct effective barriers on 11 of the 15 tributaries. Two pre-existing low-head dams, on the Great Chazy River, NY, and Lewis Creek, VT, were reconstructed during the ESLCP to block spawning runs. However, neither of these dams was consid-

Bayluscide (kg)

ered to be a complete control alternative, as extensive sea lamprey spawning habitat existed below both barriers. Assessment of the Sea Lamprey Control Program Spawning Phase Sea Lamprey Assessments Spawning phase sea lamprey were monitored by trapping with portable assessment traps (PATs); all

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Marsden et al. TABLE 2. Numbers of sea lamprey collected with portable assessment traps (PATs) from three Lake Champlain tributaries from 1982 to 1997. Sea lamprey were collected from Great Chazy River using a permanent trap beginning in 1995, with higher capture effectiveness than PATs; totals do not include sea lamprey from Great Chazy River. Year 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997

Stone Bridge Brook NA NA NA NA NA NA NA 108 350 91 16 12 10 13 8 2

Indian Brook NA NA NA NA NA NA NA 61 410 184 93 59 83 125 80 8

sea lampreys collected in the traps were removed from the stream. Three streams were monitored throughout the experimental program; Lewis Creek, starting in 1982, and Indian Brook and Stone Bridge Brook starting in 1989. In each stream, catch dropped below 10% of pre-control levels by the end of the control program (Table 2). Indirect indices of population size, weight, and sex ratio were also monitored during the spawning season. The sex ratio of spawning sea lamprey captured with PATs shifted toward a higher proportion of females, but the difference was not statistically significant (t-test, p > 0.05). Average weight of spawning sea lamprey did show a significant increase (t-test, p < 0.001) in Lewis Creek (Fisheries Technical Committee 1999). Nest counts were conducted annually on ten tributaries in index sections to monitor spawning activity throughout the basin. There was an overall reduction in nests to 42.6% of the pre-control (1983-1991) average (Fig. 3). The evaluation criterion for successful treatment called for a reduction in the numbers of sea lamprey nests tallied at index sites to 20% of pre-control values. This criterion was not met on either a lakewide basis or in individual streams except in the Great Chazy River, where a dam was reestablished as a sea lamprey barrier below the index section. This reduction in spawning in the Great Chazy River also accounted

Lewis Creek 149 517 670 848 600 268 224 596 489 219 231 234 421 109 59 58

Great Chazy River NA NA NA NA NA NA NA NA NA NA NA 234 NA 1,023 1,236 223

Total

765 1,249 494 340 305 514 247 147 68

for the majority of the overall reduction in nesting lakewide. Larval Phase Assessments Pre-control larval sea lamprey assessments using electrofishing CPUE were used to identify and select streams for treatment (Gersmehl and Baren 1985). Production estimates of larval phase sea lamprey were not determined for Lake Champlain tributary streams during the ESLCP. The Great Lakes Fishery Commission (GLFC) Quantitative

FIG. 3. Total sea lamprey nests counted in 10 tributaries of Lake Champlain, 1983 to 1997.

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TABLE 3. Summary of sea lamprey mortality and number of transformers estimated post-treatment on Lake Champlain tributaries. Percent sea lamprey < 100 reflects the presence of native lamprey species in tributaries. The numbers of sea lamprey transformers were derived by multiplying the proportion of transformers in samples collected by mortality survey crews by the number of all lamprey mortalities observed. Mortality counts are conservative indicators, and likely underestimate mortality in all streams.

River Salmon River Little Ausable River Ausable River Boquet River Beaver Brook Putnam Creek Lewis Creek Mount Hope Brook Stone Bridge Brook Trout Brook Great Chazy River Saranac River Poultney River Hubbardton River

Treatment Year 1990 1994 1990 1994 1990 1994 1990 1994 1990 1990 1994 1990 1994 1991 1995 1991 1995 1992 1996 1992 1992 1996 1992 1996

Sea lamprey mortality count 64,828 63,648 122,456 38,274 24,506 69,243 6,325 6,564 1,005 30,230 20,659 25,942 41,408 26,970 11,308 545 157 132,796 22,712 394 197 6,759 182 20

Assessment Survey (QAS) protocol (Slade et al. 2003) was used to evaluate larval populations in two Lake Champlain tributary systems in 1999 (Dean and Zerrenner 2000), and an additional two tributaries were evaluated in 2000. In the future, it is anticipated that more stream surveys will be done using the QAS protocol. Assessment of TFM Treatment Effectiveness Mortality resulting from TFM treatments was assessed following all treatments. Assessment crews waded or canoed in nearly all treated stream sections and counted all visible dead ammocoetes, generally beginning 24 hr behind the leading edge of the TFM block (Table 3). Samples of dead ammocoetes were also collected for later identification to species. Counts were minimal estimates of mortality, as accuracy was affected by field conditions such as light, water clarity, vegetation, water depth,

Percent sea lamprey 99.96 99.94 99.94 99.52 66.78 71.03 99.40 97.97 98.14 96.18 98.05 97.95 92.81 99.36 99.87 70.9 63.3 99.85 99.95 100 66.11 72.61 100 100

Number of transformers 12,976 71 31,411 631 2,310 1,081 1,197 72 131 3,121 1,114 4,297 871 4,252 1,433 277 75 41,706 395 3 0 989 8 0

Percent transformers 20.0 0.1 25.7 1.7 9.4 1.6 18.9 1.1 13.0 10.3 5.4 16.6 2.1 15.8 12.7 50.8 47.8 31.4 1.7 0.8 0 14.6 4.4 0

substrate characteristics, and consumption by scavengers (Fisheries Technical Committee 1999). The effectiveness of TFM treatments was evaluated using ammocoete abundance (CPUE) data collected at index stations before and after treatment. The majority of electrofishing was done with a 250volt DC generator mounted in a canoe. AbP-2 backpack electrofishing units (Slade et al. 2003) were used in instances where access was difficult and in streams too small to accommodate the canoe unit. Electrofishing stations were selected throughout stream reaches infested with sea lamprey in optimal habitat, and were used to monitor the sea lamprey population throughout the ESLCP. Stations were moved slightly in some instances to accommodate changes in stream conditions such as water level and substrate changes. A treatment was considered to be successful if post-treatment population densities at index stations, as indicated by relative abundance estimates,

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TABLE 4. Comparison of sea lamprey ammocoete catch rates before and after treatment of tributary streams between 1990 and 1996. CPUE refers to catch per unit effort equivalent to 30 min of electrofishing per standard-sized plot sampled. Pre-treatment survey results Total River year catch CPUE Salmon River 1990 208 52.0 1994 1,050 87.5 Little Ausable River 1990 598 66.4 1994 684 85.5 Ausable River 1990 31 7.8 1994 469 67.0 Boquet River 1990 —a —a 1994 170 24.3 Beaver Brook 1990 —a —a Putnam Creek 1990 198 66.0 1994 922 84.0 Lewis Creek 1990 169 56.3 1994 544 49.5 Mount Hope Brook 1991 101 101.0 1995 216 31.0 Stone Bridge Brook 1991 232 116.0 Trout Brook 1995 80 10.0 Great Chazy River 1992 562 80.3 1996 561 80.1 Saranac River 1992 456 57.0 Poultney River 1992 248 13.0 1996 459 23.0 Hubbardton River 1992 72 7.2 1996 18 1.0 aDue to flow conditions, pre-treatment surveys were not conducted 1990 treatment.

did not exceed 10% of pre-treatment levels. This evaluation criterion was met or exceeded in seven of the 11 streams evaluated after the first round of treatment, and nine of 11 streams treated in the second round (Table 4). The effectiveness of two treatments in 1990, on Beaver Brook and the Boquet River, could not be evaluated because high flow conditions prevented pre-treatment surveys (Fisheries Technical Committee 1999). Surviving ammocoetes tended to be larger on average than the mean length of ammocoetes in streams prior to control and most residual ammocoetes sampled the year after treatment were transformers. Low treatment effectiveness was generally attributable to field conditions unique to portions of the rivers, e.g., low TFM movement in areas of low water flow or backwaters, or presence of ground-water infusion that was inferred based on local reduction of TFM concentration. Due to restrictive permitting conditions

Post-treatment Percent survey results overall Number of Total reduction in stations catch CPUE catch rates sampled 18 4.5 91.3 4 21 1.75 98.0 12 8 0.9 98.7 9 16 1.5 95.7 11 18 4.5 41.9 4 2 0.3 99.5 7 99 12.4 —a 8 25 3.6 81.0 7 20 20.0 —a 1 14 4.6 92.9 3 285 25.9 69.1 11 15 5.0 91.1 3 20 1.8 96.3 11 34 34.0 66.3 1 8 1.1 96.3 7 0 0 100 2 0 0 100 8 7 1.0 98.8 7 0 0 100 7 102 12.8 76.4 8 286 15.0 –15.3 19 20 1.0 95.6 20 2 0.2 97.2 10 1 0.125 94.4 8 in Beaver Brook and the Boquet River prior to the

in 1992, the Poultney River was required to be treated with a dose at 0.8 times the lower of the minimum lethal concentrations as determined from both a toxicity test and the predictive pH and alkalinity chart. This lowered target concentration was due to concern over nontarget species presumed to be sensitive to TFM, including the state-listed eastern sand darter as well as several mussel species. Only 200 dead ammocoetes were counted after treatment, and the post-treatment CPUE (15.1 ammocoetes/hr) was higher than pre-treatment (13.1/hr). Modified permit conditions allowed for the second treatment in 1996 to be conducted at 1.0 times MLC as determined by bioassay, resulting in approximately 7,000 mortalities and a drop in CPUE from 23.0/30 min to 1.0/30 min (Table 4). Reestablishment of ammocoetes was documented within one to two years following treatment in all treated streams except Stone Bridge Brook and

Sea Lamprey Control in Lake Champlain Trout Brook. During the first scheduled TFM treatment of Stone Bridge Brook in 1991, the stream received simultaneous treatments at two locations, resulting in increased exposure time in the lower reaches of the stream. The number of spawning phase sea lamprey captured in Stone Bridge Brook dropped from a high of 350 in 1990 to 16 in 1992 and continued to decline to a low of 2 animals in 1997. This decline in the number of spawning adults and the lack of recolonization may be attributed to a very effective treatment in 1991 and subsequent effective spawning-phase assessment trapping operations. Trout Brook was treated in 1995 and no recolonization has been detected since then. Very low levels of ammocoetes were detected in Beaver Brook and the Saranac River by the third year after treatment. Streams in which no sea lamprey were initially found, but which have suitable sea lamprey habitat, were periodically monitored during the ESLCP. Two streams which initially harbored no sea lamprey populations were found to be infested during the ESLCP. The LaPlatte River was first surveyed in 1992; in 1993 sea lamprey were found for the first time, and in 1997 sea lamprey and silver lamprey (Ichthyomyzon unicuspis) were found. Sea lamprey were found in Mullen Brook in late 1991; only American brook lamprey had been recorded in an earlier survey. Growth rates of re-established ammocoetes were determined for eight rivers using length-frequency analysis in order to predict the age at which ammocoetes would begin metamorphosis. These data were important for predicting future treatment intervals to ensure that no ammocoetes metamorphosed prior to treatment. Growth rates ranged from a low of 15 mm/yr to a high of 45 mm/yr (Table 5). Predicted age for metamorphosis was 4+ to 5+ in most streams. Estimated growth rates in the Poultney River and Lewis Creek indicated that metamorphosis could occur after 3 years of stream growth. Assessment of Bayluscide Treatment Effectiveness Effectiveness of delta treatments was evaluated using ammocoetes in live cages in each of the five treated deltas. Up to four cages with 20 ammocoetes each were placed in the treatment zones and control cages were placed outside the treatment zone. Treatments in 1991 on four of the deltas resulted in 100% mortality of caged ammocoetes and no mortality in control cages; mortality in the Bo-

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quet River delta was 73%, and 2–6% of lamprey recovered from control cages were dead. Several cages were lost during assessment of the 1995 treatment; 100% mortality of the remaining ammocoetes occurred in the Boquet and Saranac river deltas, 96% mortality occurred in the Ausable River delta, and 87% in the Salmon River delta. Assessment of Effects on Nontarget Species The Cooperative collected routine nontarget mortality data from each stream and delta after treatment. Nontarget mortality was assessed simultaneously with sea lamprey mortality as described above. Eleven additional studies were conducted that focused on species or areas of special concern (Fisheries Technical Committee 1999). Estimates of the number of native lamprey killed by TFM treatments were obtained by counting each species in larval subsamples and extrapolating to an entire stream. One stream segment on the Ausable River was inaccessible for this survey, and one segment on the Great Chazy River was subsampled due to time constraints. Crews counted affected fish, amphibians, and large invertebrates (crayfish and mussels) in the field, or preserved samples of unidentified species for later laboratory identification. Permit conditions required collection of all dead amphibians in most New York streams. Mortality of American brook, silver and northern brook lamprey occurred after TFM treatments (Table 6). American brook lamprey had the highest mortality of native lamprey for all streams; an estimated 40,851 individuals were killed in the Little Ausable, Ausable, and Salmon rivers and Trout Brook during the two rounds of treatment. An estimated 8,619 silver lamprey were killed in seven streams, and an estimated 209 northern brook lamprey were killed in the Great Chazy River. Mortality of native lamprey was greater after the second round of stream treatments than the first, except for silver lamprey in Mt. Hope Brook and northern brook lamprey in the Great Chazy River, suggesting that individuals survived in or recolonized the treatment areas. Mortality of nontarget lamprey after Bayluscide application was qualitatively estimated by walking along the shoreline and counting dead lamprey. American brook lamprey were the only nontarget lamprey observed to be affected by Bayluscide; 1,267 dead individuals were collected on the Ausable and Salmon river deltas. Mortality on both deltas was higher after the second treatment than

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TABLE 5. Year-class, age, mean length (mm), and growth rates (during preceding year) at the end of the November growing season of re-established sea lamprey ammocoetes following TFM treatments (*indicates a treatment). The first length listed for each river is the minimum length of transformers measured pre-treatment. 1990* Age Salmon River N Mean size Growth rates (mm/yr) Ausable River N Mean size Growth rates (mm/yr) Little Ausable River N Mean size Growth rates (mm/yr) Lewis Creek N Mean size Growth rates (mm/yr) Putnam Creek N Mean size Growth rates (mm/yr) Boquet River N Mean size Growth rates (mm/yr)

1991 0+

1992 1+

1993 2+

1994* 3+

1995 0+

1996 1+

1997 2+

120

171 33

144 64 31

1148 90 26

481 115 25

4 33

131 65 32

269 93 28

127

52 40

125 64 24

389 101 37

166 117 16

25 35

9 80 45

40 105 25

127

1 27

161 62 35

682 89 27

1,273 111 22

10 37

NA 62 25

12 84 22

126

103 42

149 80 38

382 102 22

3,329 122 20

130

24 27

75 59 32

450 83 24

46 112 29

50 30

28 66 36

165 92 26

133

3 30

348 55 25

497 84 29

429 112 28

1993 0+

1994 1+

1995 2+

1996* 3+

120

10 38

85 78 41

145 104 26

361 135 31

135

14 33

43 58 25

314 93 35

523 108 15

1992* Age Poultney River N Mean size Growth rates (mm/yr) Great Chazy R. N Mean size Growth rates (mm/yr)

the first, indicating either an incomplete kill or recolonization after the first treatment. Mortality of this species was unexpected, as pre-control surveys had not detected American brook lamprey in deltas, and this species is generally assumed to live entirely within stream habitats. Excluding native lamprey, TFM mortality was associated with 47 identifiable fish species. For 38 species there were fewer than 50 mortalities per

species in any single treatment event, and an average of 2.8 or fewer mortalities per species per treatment. For nine fish species there were one or more treatments with more than 50 mortalities per species. Mortality was observed among eleven groups of invertebrates and amphibians after TFM treatments. Tadpoles (Rana spp.), salamanders (not identified to species), red spotted newts (Notophthalmus viridescens), and mudpuppies (Necturus

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TABLE 6. Mortality counts for nontarget species associated with 24 TFM treatments of Lake Champlain tributaries. Observed mortalities in the two years of treatment are listed sequentially for any species and river in which at least one treatment mortality count was greater than 50. Numbers of native lamprey are estimates derived from sub-samples. Taxa Species, rivers with mortality > 50 Lampreys American brook lamprey (Lampetra appendix) Ausable R. (12,193, 28,245), Little Ausable R. (74,184) Trout Br. (92) silver lamprey (Ichthyomyzon unicuspis) Stone Bridge Br. (224), Mt. Hope Br. (175, 15), Poultney R. (101, 2,549), Boquet R. (38, 136) Putnam Cr. (1,202, 410) Lewis Cr. (543, 3,207) northern brook lamprey (Ichthyomyzon fossor) Great Chazy R. (197, 12) Teleost Fishes stonecat (Noturus flavus) Little Ausable R. (21, 196), Salmon R. (141,185), Saranac R. (331), Great Chazy R. (5,768, 88) log perch (Percina caprodes) Ausable R. (9, 82), Lewis Cr. (248, 26), Great Chazy R. (561, 28) bluntnose minnow (Pimephales notatus) Stone Bridge Br. (725) blacknose dace (Rhinichthes atratulus) Putnam Cr. (8, 424), Lewis Cr. (66, 0) white sucker (Catostomus commersoni) Stone Bridge Br. (170), Mt. Hope Br. (2, 75) tessellated darter (Etheostoma olmstedi) Lewis Cr. (114, 4), Stone Bridge Br. (64) brown bullhead (Ameiurus nebulosus) Lewis Cr. (18, 121) chain pickerel (Esox niger) Mount Hope Br. (78, 19) longnose dace (Rhinichthyes cataractae) Lewis Cr. (53, 2) other species combined (38) Amphibians, invertebrates Frog tadpole (Rana spp.) Stone Bridge Br. (364), Great Chazy R. (1,460, 3,614) Mudpuppy (Necturus maculosus) and unidentified salamander Putnam Cr. (3, 90), Great Chazy (1,209, 442) Red-spotted newt (Notophthalmus viridescens) Mt. Hope Br. (295, 67) Crayfish (Orconectes spp.) Frog adult (Rana spp.) Two-lined salamander (Eurycea bislineata) Unidentified mussel Leopard frog (Rana pipiens) Leech (Hirudinea) Unid. worm

Total mortality

# treatments with > 50 mortalities

40,851

5

8,619

9

209

1

6,730

6

1,057

3

755

1

517

2

340

2

318

2

277

1

130

1

66

1

451

0

5,461

3

1,923

3

362

2

36 33 41 25 1 1 1

0 0 0 0 0 0 0

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maculosus) had the highest levels of mortality (Table 6). Most species for which mortality occurred in the first treatment were detected again in similar numbers after the second round of treatment, which suggests survival or recolonization after the first treatment. Bayluscide treatments caused mortality of 29 identifiable fish species. Mortality was minimal for most species except for banded killifish (Fundulus diaphanus), mimic shiner (Notropis volucellus), spottail shiner (N. hudsonius), yellow perch, emerald shiner (N. atherinoides), and white sucker (Catostomus commersoni); of the nine treatments, six treatments resulted in observed mortality of > 50 of one or more of these species. In addition, mortality of 32 mussels, 2 crayfish, 2 snails, and 1 frog tadpole was observed (Fisheries Technical Committee 1999). The effect of TFM treatment on eastern sand darters was assessed in situ using 91 individuals held in cages in stream sections exposed to TFM and upstream in a control site during the 1990 and 1994 Lewis Creek treatments. No mortalities occurred during the 1990 treatment, and two mortalities, possibly unrelated to treatments, were documented among 24 darters held within the TFM block in 1994 (MacKenzie 1991, 1995). Caged eastern sand darters were also held in situ during the 1992 and 1996 TFM treatments of the Poultney River; no mortalities occurred. Short-term and long-term effects of TFM on fish and invertebrates were monitored in Lewis Creek, Trout Brook, and the Little Ausable and Ausable River deltas. Community level analysis of Lewis Creek showed no adverse effects on macroinvertebrates, including pollution-sensitive and TFM-sensitive species, after TFM treatments (Langdon and Fiske 1991, VTDEC 1994). Density, species richness, and EPT (Ephemeroptera, Plecoptera, and Trichoptera) Index were slightly greater post-treatment in Trout Brook, though the difference was not statistically significant (Mann-Whitney U Rank Sum test, p > 0.05; VTDEC 1996). A modified Index of Biotic Integrity applied to fish species showed identical scores before and after treatment, though abundance of individual species did change after treatment (VTDEC 1996). Community sampling of invertebrates in the Little Ausable and Ausable River deltas showed no significant differences between pre-and post-treatment using TFM (Gruendling and Bogucki 1993a). Statistically significant (Wilcoxon Rank Sum test, p < 0.001) declines in density occurred after

Bayluscide treatment of the Little Ausable River delta in four of eight macroinvertebrate orders: Gastropoda, Pelecypoda, Diptera (chironomids), and Hirundinea (Gruendling and Bogucki 1993b). One year later, Hirudinea, Gastropoda, and Pelecypoda remained significantly below pre-treatment densities (Wilcoxon Rank Sum Test, p < 0.05). Gastropoda, Pelecypoda, Oligochaeta, Hirudinea, and Diptera declined in density (Wilcoxon Rank Sum Test, p < 0.005) in the Ausable River delta after Bayluscide treatment, but no significant change was seen in Amphipoda, Isopoda, or Ephemeroptera. A year later, Diptera, Gastropoda, and Pelecypoda remained below pre-treatment densities (Wilcoxon Rank Sum Test, p < 0.001; Gruendling and Bogucki 1993b). However, 4 years after the 1991 Bayluscide treatment of the Little Ausable and Ausable deltas, mussel and gastropod densities had recovered to pre-treatment levels (Lyttle 1996). Hirudinea and Diptera were not reassessed. Native mussels were monitored in the Poultney River and Little Ausable and Ausable River deltas. No stress (gaping, loss of orientation or filtering activity) was noted among 10 mussel species in beds during the 1992 Poultney River treatment (Fichtel 1992). Gravid mussels held within the Poultney River treatment area did not prematurely release glochidia during and for at least five days after the 1996 treatment, and no glochidia were found in drift net samples below the TFM application point (Lyttle and Pitts 1997). No statistically significant mortality occurred in mussels held in cages on the Little Ausable and Ausable River deltas during TFM treatment of their respective rivers; four of 180 caged unionids died (Gruendling and Bogucki 1993a). High mortality of eastern elliptio (Elliptio complanata; 9.1–70%) and eastern lampmussel (Lampsilis radiata; 52.5–94%) occurred in cages during Bayluscide treatment of Little Ausable and Ausable River deltas, whereas no mortality occurred in controls located outside the treatment area (Gruendling and Bogucki 1993b; Table 7). Density of Lampsilis radiata and Elliptio complanata after treatment on both deltas was less than pre-treatment (Wilcoxon Rank Sum Test, p < 0.001); neither species reached pre-treatment density after 1 year. Laboratory studies estimated a 24 hr LC50 of 998 ng/L of Bayluscide for E. complanata, and 178 ng/L for L. radiata (Gruendling and Bogucki 1993b). The highest mean concentration achieved within a 24 hr period after treatment was 298.2

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TABLE 7. Mean percent mortality of unionid mussels in cage experiments and ambient conditions in two deltas treated with Bayluscide. Ten replicates of cages and field plots were measured in the Little Ausable River, and 11 each in the Ausable River. ND = no data. N

Caged Mean

SD

N

Little Ausable River Elliptio complanata control

100 10

70.0 0

34.3 0

202

42.0 ND

25.2

Lampsilis radiata control

100 10

94.0 0

8.4 0

56

80.9 ND

26.2

Ausable River Elliptio complanata control

110 10

32.7 0

32.0

33

10.8 ND

18.2

Lampsilis radiata control

110 10

73.6 0

33.2

387

62.8 ND

26.1

ng/L on the Little Ausable River and 167.7 ng/L on the Ausable River. Salmonid Wounding and Survival Lake Trout Intensive gill-netting of lake trout was conducted from 1982 to 1997 to collect CPUE data as an index of abundance. Assessment gillnets were 1.8 m deep, 122 m long, with eight 15-m panels of multifilament nylon ranging (in sequence) from 6.4 to 15.3 cm stretch mesh in 1.3 cm increments. Use of spreader bars, float lines versus floats, old versus new nets, and types of leads varied between states and among years, leading to possible variation in catch rates. Nets were set between June and August, primarily in the Main Lake (zones 3A and 3B; Fig. 1), though sampling also occurred in zones 2B, 2C, 3C, 4A, 4B, 5A, 5B, and 5C. Lake trout were measured (TL) and weighed on board, and lamprey wounds and scars were recorded using standard criteria (King and Edsall 1979). Lake trout in Lake Champlain were marked with one of five fin clips in a five year-rotation, so that ages of captured fish could be determined using a combination of lengthfrequency analysis and fin clip information; scales were read when these data were in doubt. Lengthfrequency and clip data were deemed to be reliable methods for aging up to at least age 6. CPUE of lake trout in assessment gillnets increased over the study period in zones 3A and 3B,

Field Plots Mean

SD

the primary lake trout range (Fig. 4). CPUE outside zones 3A and 3B also increased, from a mean of 1.77 (± 0.295, 90% confidence interval) lake trout per net lift pre-treatment (1982–1990) to a mean of 3.96 (± 0.375, 90% confidence interval) post-treatment (1991–1997). This difference was statistically significant using a nonparametric Mann-Whitney test (p ≤ 0.000). In open water creel surveys, total catch increased 76% from an estimated 23,345 (± 3,270, 90% confidence interval) in 1990 to 41,162 (± 4,999, 90% confidence interval) in 1997, accompanied by no significant change in fishing effort. Average weight of lake trout increased by 7% over the same period. The proportion of lake trout > 635 mm in the harvest increased by 42%. Survival estimates were calculated based on CPUE data that had been corrected for gill net selectivity, swimming speed, and probability of capture by means other than gilling (Fisheries Technical Committee 1999). Selectivity curves were developed for each pair of mesh sizes, assuming that probabilities of capture for a given mesh are normally distributed around an optimum fish length for that mesh (Holt 1963, Fisheries Technical Committee 1999). The selectivity curves were adjusted to account for the tendency for larger fish to have high probabilities of encountering gill nets because of their faster swimming speed and greater foraging range (Rudstam et al. 1985). The resulting selectivity curves were used to correct data from all years and both states’ gill netting. Extraordinarily

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FIG. 4. Catch-per-unit-effort (net lifts) of lake trout in zones 3A and 3B in Lake Champlain from 1982 to 1997. Bars represent a 95% confidence interval. N refers to the number of net lifts. high catches in 1984 and 1996 were considered to be anomalies, and the CPUE data for these years were derived by running two linear regressions, using pre-control CPUE data (1982 to 1990) for 1984, and using post-control CPUE data (1991– 1997) for 1996. The truncated Chapman-Robson method was used to estimate survival rates of individual year classes for age 3–6 and 4–9, and the Heincke estimate was used for age 3–4 (Fisheries Technical Committee 1999). Lake trout younger than age 3 were eliminated from the survival estimates because these fish were not fully vulnerable to the gill nets. Non-Seneca Lake strain lake trout were also excluded where possible to eliminate the potential bias from a greater preponderance of non-Seneca Lake strain lake trout stocked in earlier years. Survival estimates by year class of lake trout from age 3 to age 4 increased from 0.35 pre-control to 0.44 post-control (p < 0.015); survival of age 3–6 lake trout increased from 0.47 pre-control to 0.52 postcontrol (p < 0.069). Survival of age 5–9 lake trout (0.57 pre-control) also did not change significantly (p < 0.301; Table 8); however, this comparison was had only three year classes in the post-control data

set. The small number of year classes in the postcontrol data set limits these survival estimates, so the data were re-analyzed by netting year. After weighting age 3 fish to a uniform number to reduce the effect of highly variable survival from stocking to age 3, netting year survival estimates yielded similar results to year-class survival estimates, except that age 5–9 survival increased significantly in netting-year analysis (Table 8). Number of year classes of lake trout present in the lake increased from eight in 1982 to 12 in 1997. There was a significant decrease in length-at-age from the pretreatment to the post-treatment period (1982–90 vs. 1991–97) for seven of the eight year classes analyzed (t-test, p < 0.05); there was also a significant decrease in length-at-age during the pre-treatment period (1982–85 vs. 1986–90) for ages 5 through 10 (t-test, p < 0.05). Fishing mortality rates were estimated using tagged fish and creel surveys. Lake trout have been tagged annually since 1988 with anchor tags. Creel surveys conducted in 1990, 1991, and 1997 generated sufficient data to estimate fishing mortality. Lake trout angler catch is limited to fish greater than 38 cm, up to three fish per day, year round.

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TABLE 8. Survival estimates for lake trout before and after sea lamprey control in Lake Champlain. Data were compared using a one-tailed t-test. Age 3–4 3–6 5–9

by year-class Survival SD 0.35 0.07 0.44 0.06

Period pre-control post-control

Interval 1979–87 1988–93

pre-control post-control

1979–87 1988–91

0.47 0.52

pre-control post-control

1979–85 1986–88

0.57 0.58

0.015

Interval 1983–90 1991–97

0.05 0.03

0.069

1985–90 1991–97

0.47 0.51

0.05 0.03

0.037

0.03 0.01

0.301

1986–90 1991–97

0.51 0.59

0.06 0.03

0.005

The estimated total number of fish harvested with tags in the year following tagging was divided by the number of fish tagged in the previous year. Using a tag loss rate of 0.26 estimated by Fabrizio et al. (1996), fishing mortality was 0.14 in 1990, 0.11 in 1991, and 0.14 in 1997. Creel surveys yielded annual mortality rate estimates from catch curve analysis of 0.79 in 1990 (pre-control) and 0.30 to 0.39 in 1997 (post-control) for age 6-9 lake trout. As fishing mortality did not appear to change materially over the period of study, the changes in survival represent decreases in natural mortality. Collection of wounding and scarring data began in 1982. Wounds were evaluated as the sum of all Type AI, AII, and AIII wounds combined; scars were type AIV marks. Wounding and scarring was relatively low (51 wounds and 102 scars per 100 lake trout) in the early 1980s, and rose to a peak of 73 wounds per 100 lake trout in 1991 and 185 scars per 100 lake trout in 1992 (Fig. 5). Subsequent to inception of the control program, the wounding and scarring numbers returned to mid-1980s levels. An independent samples t-test was performed for wounds per lake trout and scars per lake trout for each size class and all size classes combined for pooled pre-treatment (1982–1991) and post-treatment (1992–1997) samples. There was a significant decrease in wounds and scars in comparisons of each individual size class (maximum p < 0.001), and when all size classes were combined (maximum p < 0.022). Wounding and scarring rates were also examined by adjusting for the relative number of lamprey-vulnerable lake trout in the lake each year. Population estimates for each year were not accurate because of highly variable recruitment of age-3 lake trout to the gill nets, so average catchper-net-lift was used as a relative index of abundance. Analysis using this adjustment indicated that

p-value

by netting year Survival SD 0.35 0.08 0.43 0.06

p-value 0.021

significant post-control reduction in wounding and scarring occurred in the three smallest size classes (p < 0.05). However, this analysis cannot account for changes in sea lamprey prey selection as a result of changing predator/prey ratios during the period. Other Salmonids Survival of adult Atlantic salmon was assessed using the number of fish returning to the Saranac River sport fishery in fall creel surveys, passage at the Willsboro Fishway on the Boquet River, and by fall electrofishing surveys conducted in the Inland Sea at Sandbar Bridge and the Lamoille River, tributary to Malletts Bay. Average returns of fish sampled in the Saranac River and Willsboro Fishway increased in all size-classes, up to 4.8 times higher in post-treatment relative to pre-treatment years

FIG. 5. Sea lamprey wounding data for lake trout collected in zones 3A and 3B in Lake Champlain between 1982 and 1997. Wounds are the sum of AI—AIII wounds. Vertical line indicates beginning of control program.

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Marsden et al.

TABLE 9. Returns of Atlantic salmon to Saranac River, as sampled in the fall creel survey (estimated angler catch at age), the Willsboro fishway, and the Lamoille River and Sandbar Bridge sites sampled by electroshocking. Data for the Willsboro fishway, Lamoille River, and Sandbar Bridge are mean numbers of returns per year. 1

age (lake-year) 2 3

Site and year Saranac River 1991 1996

4

80 157

16 77

8 33

0 4

Willsboro fishway 1988–92 1993–98

10.3 31.5

7.0 8.0

0.1 2.5

0 0

Sandbar Bridge, Inland Sea 1987–1992 34.8 1993–1997 81.6

18.5 14.8

2.5 1.2

0 0.6

Lamoille River, Malletts Bay 1987–92 37.3 1993–97 64.4

19.2 27.8

2.3 4.2

0 0.4

(Table 9). Returns of 1-lake-year salmon increased 3.5-fold (based on median values) in the Inland Sea; 4-lake-year salmon were noted for the first time after control, but returns of 2- and 3-lake-year fish did not change substantially. Data on returns of salmon to the Lamoille River were difficult to interpret, due to dramatic annual changes in the river flow exacerbated by water retention for hydropower generation. Estimated catch of salmon in the Saranac River decreased (0.056% to 0.018% returns per smolt stocked) in spring creel surveys and increased (0.011% to 0.035%) in fall creel surveys. Estimated returns per smolt stocked in the Main Lake open water fishery increased from 0.52% to 1.63%. There was little change in the condition factor for Atlantic salmon sampled throughout the lake. Angler harvest of rainbow trout in the Saranac River was assessed as part of the evaluation program, but did not demonstrate an increase in the catch; however few fish were observed by creel clerks. Rainbow trout catch in other tributaries was not evaluated. Estimated rainbow trout catch in the Main Lake increased from 7 ± 11 (90% confidence interval) fish in 1990 to 106 ± 82 (90% confidence interval) in 1997. An increase in brown trout caught per smolt stocked was seen in the Main Lake, Mal-

letts Bay, and Inland Sea, but a decrease was seen in the Saranac River creel data. Numbers of larger, older fish reported caught in the Saranac River increased, but these increases were not reflected in nearshore electrofishing surveys and fish handled by creel agents during Saranac River spring creel surveys. Sea lamprey wounding rates on rainbow trout, brown trout, and Atlantic salmon generally decreased between pre-control and post-control periods. Trends in the data are difficult to ascertain due to low and highly variable annual catches in each sample type (seasonal gillnets, electrofishing, creel, and fish passage facilities, or fishways), and paucity of data prior to and after control. Post-treatment wounding rates for Atlantic salmon decreased between 40 and 74% among three size-classes returning to the Willsboro Fishway and two size classes sampled during open water creel surveys in the Main Lake (Table 10). Wounding rates among Atlantic salmon sampled by electrofishing in Malletts Bay and the Inland Sea did not show significant declines in wounding for any size-classes; in over half of the size-class comparisons, wounding rates actually increased between 10 and 123% (Table 10). A decrease in wounding of 83% was observed in Winooski River spring-run rainbow trout for all size-classes combined, but could not be statistically evaluated because wound data per individual fish were not available for the pre-control data. Changes in wounding rates for brown trout could not be evaluated due to small sample sizes. Cost/Benefit Analysis The ESLCP generated estimated 1990 discounted benefits of $29,379,211 and had discounted costs of $8,447,011, resulting in a net benefit of $20,902,200 or a benefit:cost ratio of 3.48:1 (Gilbert 1999a). Success of sea lamprey control induced members of an estimated 32,528 households to increase their annual participation in water-based recreation on Lake Champlain by 219,564 days during the 8-year period and spend an additional $8.8 million on these activities (Gilbert 1999a). If sea lamprey control is continued it is estimated that members of 92,025 households currently recreating on Lake Champlain, and members of 58,542 households not currently recreating on Lake Champlain, will increase their annual participation by 1.5 million days and generate $59.3 million in additional annual water-based recreation expenditures.

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TABLE 10. Sea lamprey wounding rates (sum of type AI–AIII wounds per 100 fish) by size group (mm TL) for adult landlocked salmon captured at the Willsboro Fishway, Main Lake open water creel surveys, and electroshocking surveys in the Lamoille River and Sandbar Bridge sites, pre- and post- sea lamprey control. Data were compared using a one-tailed t-test. Willsboro fishway Size group 432–532 533–634 635–736

N 43 80 32

Pre-control 1985-1992 Mean ± SD 51 ± 80 73 ± 89 156 ± 146

N 6 40 3 49

Pre-control 1990 Mean ± SD 17 ± 41 25 ± 54 167 ± 58 33 ± 63

N 101 157 30

Post-control 1993-1998 Mean ± SD 22 ± 46 44 ± 69 40 ± 62

% change –57 –40 –74

P-value 0.014 0.007 < 0.001

N 89 138 13 240

Post-control 1997 Mean ± SD 8 ± 31 15 ± 43 46 ± 78 14 ± 42

% change –53 –40 –72 –42

P-value 0.255 0.100 0.013 0.024

N 6 262 185 36

Post-control 1993–1997 Mean ± SD 58 ± 64 53 ± 74 71 ± 82 113 ± 131

% change +123 +75 –14 +47

P-value 0.094 0.001 0.122 0.107

N 17 241 156 29

Post-control 1993–1997 Mean ± SD 12 ± 33 34 ± 52 65 ± 90 79 ± 94

% change +120 –19 +10 –24

P-value 0.007 0.120 0.280 0.169

Main Lake Size group 432–532 533–633 634–736 All Sizes

Lamoille River (Malletts Bay) Size group < 432 432–532 533–634 635–736

N 19 200 116 31

Pre-control 1986–1992 Mean ± SD 26 ± 45 32 ± 56 83 ± 93 77 ± 92

Sandbar Bridge (Inland Sea) Size group < 432 432–532 533–634 635–736

N 17 191 114 47

Pre-control 1986–1992 Mean ± SD 0 42 ± 79 59 ± 75 104 ± 118

As part of a 1997 angler survey, current and noncurrent salmonid anglers were asked if they would increase number of days fished annually on Lake Champlain if sea lamprey control is continued (Gilbert 1999b). The estimated total increase was 1.2 million days annually and average increase ranged from 14.3 days (current salmonid anglers) to 12.6 days (non-current, non-salmonid). This increase is expected to generate an estimated $42.2 million annually in fishing-related expenditures. In addition, an estimated 17,298 Lake Champlain anglers (20.5% of all Lake Champlain anglers) who

fish other lakes said they would increase the number of days they fish Lake Champlain to 16 days. Owners of 98 fishing and fishing-related businesses serving Lake Champlain anglers were not able to estimate the percentage of $5.5 million Lake Champlain-based 1997 gross fishing/fishing-related income attributable to the ESLCP; however, 48.5% of these businesses expanded during the ESLCP and business-owners attributed 29.2% of expansion directly to the program (Gilbert 1999c). Another 35.4% of business owners plan further expansion and 21% of planned expansion was directly attrib-

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utable to anticipated continuation of sea lamprey control on Lake Champlain. DISCUSSION The 8-year ESLCP in Lake Champlain successfully achieved the primary objectives of reduction in the abundance of ammocoete and parasitic phase sea lamprey. A decrease in salmonid wounding and scarring rates was observed, primarily in lake trout, and survival of lake trout increased significantly, but not substantially, between pre- and post-control periods. There was a net benefit to the economy of the region as a consequence of increased recreational use of Lake Champlain and its fisheries directly related to sea lamprey control. Negative effects on nontarget species did result from both TFM and Bayluscide treatments, however these were largely temporary; similar or higher mortalities in second treatments indicated minimal population-level impacts for most nontarget species. The conclusion that spawning phase sea lamprey populations have been reduced by two rounds of treatments in Lake Champlain is based on spawning phase trapping in three streams, nest counts in 10 streams, and indirect evidence from lake trout wounding. These data have a degree of uncertainty, however. Pre-control trapping data on spawning phase sea lamprey abundance are only available from a single tributary, Lewis Creek, monitored since 1982, and from 3 years of data each from Stone Bridge Brook and Indian Brook. While sea lamprey declined in each of these streams after each treatment, spawning phase sea lamprey numbers were as low or lower in Lewis Creek in 1982 and 1988 as they were after the first round of treatment. These longer-term data suggest that lamprey populations have undergone severe fluctuations prior to recent control efforts. However, trap efficiency may have varied due to changing flow conditions, which may affect accuracy of these data as an estimator of relative abundance. Nest counts declined after treatment in all assessed streams except the Poultney River; the largest single reduction in nests occurred in the Great Chazy River as a result of dam re-construction. Nest counts have not been validated as an index of spawning phase abundance. However, nest counts in the untreated Pike River can be used to evaluate changes in the spawning population. Pike River nest abundance declined after control began, suggesting that the overall sea lamprey population in Lake Champlain was reduced. Three explanations have been suggested for the

relatively low pre-control wounding rates and nest counts, followed by increases in the late 1980s: natural fluctuations in sea lamprey abundance; limited ammocoete survival due to poor water quality in some tributaries, followed by improved water quality; or increased salmonid populations due to stocking and consequent increase in the lamprey food supply. A sufficiently long-term database on sea lamprey abundance in Lake Champlain does not exist to fully examine the first possibility. Similarly, stream water quality data are insufficient to validate the possibility of suppression of ammocoete survival by pollution. Certainly many rivers, such as the LaPlatte River and Winooski River in Vermont and the Pike River in Quebec, had episodic low dissolved oxygen (unpubl. data) during the 1980s due to high inputs of agricultural and municipal effluents, but the effect on sea lamprey cannot be estimated with any degree of certainty. Sewage treatment upgrades and higher minimum flows resulting from hydropower relicensing have improved water quality in the Winooski River. Young et al. (1996) argue that lake trout stocking could be a factor in sea lamprey population increases, by increasing potential prey and therefore growth of sea lamprey. However, the effect of salmonid stocking on sea lamprey in Lake Champlain should have been seen within a decade of the first substantial stockings, i.e., by 1984, but no increase in growth or number was detected. In addition, the apparent increase in lake trout during the 1990s may either have been due to increased stocking, or to reduction in the number of sea lamprey consequent to control. Population estimates for spawning phase sea lamprey would facilitate evaluation of these effects. Lake trout wounding rates in Lake Champlain are high compared to the Great Lakes; this may be due in part to the high potential for lamprey production in the basin. Average annual wounding rates for lake trout > 431 mm ranged from 33.3 to 80% precontrol, and 7.8 to 56.9% post-control. Wounds per 100 lake trout > 431 mm ranged from 48 to 73 precontrol and 24.4 to 52.2 post-control, compared with a peak of 42 wounds per 100 lake trout > 431 mm in Lake Erie (Sullivan et al. 2003). A relatively large number of tributaries (approximately 105 permanent streams) drain into a relatively small lake; the ratio of drainage area to lake area is over five times greater than any of the Great Lakes. In contrast to the Great Lakes, where 8% of the tributaries produce lamprey (Morman et al. 1980), approximately 20% of the tributaries in the Lake Champlain drainage produce lamprey. Unlike the Great

Sea Lamprey Control in Lake Champlain Lakes, Lake Champlain does not contain coho (O. kisutch) and chinook salmon (O. tshawytscha) as alternate prey, so that lamprey attacks are concentrated on lake trout. Wounding rates did decrease significantly for most size-classes of lake trout after initiation of sea lamprey control; however, this analysis is confounded by the probable increase in the salmonid prey base during the study period. Post-control wounding rates in Lake Champlain have not yet approached the low wounding rates targeted in Lake Erie (< 5 wounds per 100 lake trout > 431 mm; Sullivan et al. 2003) or Lake Ontario (< 2 AI wounds per 100 lake trout > 431 mm; Larson et al. 2003) Despite high wounding rates, lake trout survival in Lake Champlain is high compared to the Great Lakes, and increased through the period from 1979 to 1997. Kitchell and Breck (1980) hypothesized that the duration, and therefore the possible lethal effect, of lamprey attacks decreases as prey abundance increases. Therefore, as the population grew through stocking, the number of lake trout deaths due to lamprey may have decreased. In addition, the majority of stocked lake trout were from the Seneca Lake strain, which may be more resistant to lamprey predation than other strains stocked abundantly in the Great Lakes (Swink and Hanson 1986). Survival estimates for lake trout in Lake Champlain are comparable with those from Seneca Lake (Engstom-Heg et al. 1990). Survival of older lake trout was greater than for younger lake trout, possibly reflecting increased resistance to lamprey attack by older, larger fish (Swink 1990). Curiously, lake trout showed a trend before and during the ESLCP of decreasing length-at-age, although length-at-age still exceeds that of lake trout from Seneca Lake (Engstrom-Heg and Kosowski 1991). Higher survival coupled with increased stocking numbers may have led to an increase in intra-specific competition and consequent reduction in growth. Based on these comparisons of Lake Champlain and Great Lakes lake trout wounding and survival rates, the Cooperative established an acceptable long-term wounding rate objective of 25 wounds per 100 lake trout in the 533–633 mm length class, with an ideal rate of 10 wounds per 100 lake trout of this size for Lake Champlain (Fisheries Technical Committee 2001). Evaluation of wounding rates is confounded by the fluctuating lake trout populations resulting from changes in the stocking program, indirect evidence of highly variable early survival (stocking to age 3), difficulties with evaluation of catch data, and

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paucity of catch data on the non-lake trout salmonids. In addition, nest counts and lake trout wounding rates were higher in 1988-1991 than in previous years. The effect of the control program therefore appears to be large if compared to the years immediately preceding the first treatment, but less dramatic if compared to data from 1982–1987. Mortality among certain nontarget species throughout the ESCLP, though high, was generally consistent with predictions stated in the project EIS. As expected, Bayluscide treatments caused higher mortality than TFM treatments; this difference substantially increased total nontarget mortality. Full evaluation of the impact of lampricide treatments on nontarget species is hindered by the lack of population data for these species in the Lake Champlain basin. The contrast between higher Lake Champlain and lower Great Lakes nontarget mortalities may be due to differences in monitoring and assessment methods for nontarget mortality, which were necessarily more rigorous in Lake Champlain than the standard methods used in the Great Lakes due to permitting requirements. Assessments in Lake Champlain may therefore have documented a higher proportion of the actual nontarget mortalities. For example, assessment crews examined streams approximately 24 hours after initiation of treatment rather than following the leading edge of the treatment pulse as in the Great Lakes, and thus were more likely to pick up organisms that had a delayed response to the lampricide. Refinement of TFM and Bayluscide application methods may reduce nontarget mortality. Refinements under consideration include more rigorous monitoring of stream pH and alkalinity cycles, which substantially affect toxicity; use of lower TFM concentrations at the primary application point combined with use of intermediate application points to maintain the chemical concentration; use of TFM:Bayluscide mixtures to increase efficacy of stream treatments, and reducing the area of deltas treated with Bayluscide by targeting locations where ammocoetes are likely to be concentrated, based on non-wadable waters larval assessment techniques (Slade et al. 2003). Following completion of the ESLCP on Lake Champlain, the Cooperative developed an extensive, integrated management approach to long-term sea lamprey control (Fisheries Technical Committee 2001). Future control may expand to include treatment of previously untreated tributaries such as the Winooski River and Pike River. Control methods being considered for implementation in the long-

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term sea lamprey control program include continued use of TFM and Bayluscide, and alternative methods such as use of different types of barriers (electrical and physical) to block upstream migration of spawning sea lamprey, and removal of spawning sea lamprey through trapping. Barrier dams are not feasible for many tributaries, unless passage of migratory species is mitigated. The lack of recolonization of Stone Bridge Brook following treatment in 1991 throughout 1997 (the last year in which monitoring occurred) suggests that complete elimination of sea lamprey ammocoetes from a stream may result in long-term reduction of the spawning population due to absence of attractants produced by ammocoetes (Sorenson and Vrieze 2003). Research into the importance of pheromones as attractors for spawning sea lamprey could be conducted at a number of small tributaries in the basin. Use of other techniques such as sterile-malerelease (Twohey et al. 2003) will be considered if future research demonstrates their efficacy. The Cooperative completed a supplemental EIS for long-term sea lamprey control to meet NEPA requirements for use of federal funds and USFWS staff involvement in the program (Fisheries Technical Committee 2001). Necessary state permits for tributary-specific control operations must also be obtained, as well as Canadian regulatory approvals for control in the Pike River system. The cost-benefit data clearly support continued control of sea lamprey in Lake Champlain. However, the program continues to face resistance from a vocal minority of local individuals and organizations who object to sea lamprey control largely based on their perceptions of risk to nontarget organisms and general opposition to use of pesticides in the environment. Research to document the risks to potentially sensitive nontarget aquatic species from use of lampricides and other control methods, and commensurate refinement of control methods to minimize the risks of nontarget impacts will be integral elements of the long-term program. Due to the relatively small size of Lake Champlain and recent initiation of sea lamprey control, the lake presents some important contrasts with the Great Lakes and opportunities for research and management. For example, a lake-wide sea lamprey tagging study to examine movement and relative contributions of individual streams to the parasitic population is underway. Because a number of tributaries have never been treated, the opportunity exists to examine responses of untreated sea lamprey populations to sea lamprey control. Recent research

suggests that sea lamprey may respond to treatment by increasing growth, which decreases the size and age at metamorphosis (Zerrenner 2001). This research will be enhanced by progressive implementation of GLFC QAS protocols for habitat and ammocoete density assessment in Lake Champlain, enabling estimation of production in individual streams (Slade et al. 2003). ACKNOWLEDGMENTS We thank Pat Festa, Angelo Incerpi, David Johnson, Chet MacKenzie, Paul Neth, David Nettles, Gary Neuderfer, Dan Plosila, Larry Strait, and David Tilton for their contributions to the sea lamprey control program. We also acknowledge the contributions of the late Gary Steinbach and Robert Engstrom-Heg. This work was funded by Federal Aid to Sport Fish Restoration Act Projects FA-40-R (New York) and F-23-R (Vermont), New York State Conservation Fund appropriations, a special Congressional appropriation through the Great Lakes Fishery Commission, and the Lake Champlain Special Designation Act of 1990. REFERENCES Anderson, B.E., Guilmette, J.R., and Dudley, J.B. 1985. Preliminary feasibility study for sea lamprey barrier dams on Lake Champlain tributary streams. Bureau of Fisheries. NYSDEC, Ray Brook, NY. Anderson, J.K. 1978. Lake Champlain fish population inventory, 1971–1977. Fisheries Technical Committee, Lake Champlain Fish and Wildlife Management Cooperative, Essex Junction, VT. Bills, T.D., Boogaard, M.A., Johnson, D.A., Brege, D.C., Scholefield, R.J., Westman, R.W., and Stephens, B.E. 2003. Development of a pH/alkalinity treatment model for applications of the lampricide TFM to streams tributary to the Great Lakes. J. Great Lakes Res. 29 (Suppl. 1):510–520. Daniels, R.A. 2001. Untested assumptions: the role of canals in the dispersal of sea lamprey, alewife, and other fishes in the eastern United States. Env. Biol. Fishes 60:309–329. Dean, M., and Zerrenner, A. 2000. Assessment of sea lamprey habitat and the sea lamprey population of the Pike River and Morpion Stream, Quebec, Canada. Final report, Lake Champlain Basin Program, Grand Isle, VT. Engstrom-Heg, R., and Kosowski, D.H. 1991. Evaluation of fishery impacts of lampricide treatments in the Seneca Lake system. Bureau of Fisheries, NYSDEC, Avon, NY. ———, Gersmehl, J.E., LaBar, G.W., and Gilbert, A.H. 1990. A comprehensive plan for the evaluation of an

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