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North American Journal of Management Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/ujfm20 Lake Whitefish in Lake Champlain after Commercial Closure and Ecosystem Changes Seth J. Herbst a c , J. Ellen Marsden a & Stephen J. Smith b a Rubenstein School of Environment and Natural Resources, University of Vermont, 81 Carrigan Drive, Burlington, Vermont, 05405, USA b U.S. and Wildlife Service, Lake Champlain Fish and Wildlife Resources Office, 11 Lincoln Street, Essex Junction, Vermont, 05452, USA c Department of Fisheries and Wildlife, Michigan State University, 13 Natural Resources Building, East Lansing, Michigan, 48824-1222, USA Available online: 27 Dec 2011

To cite this article: Seth J. Herbst, J. Ellen Marsden & Stephen J. Smith (2011): Lake Whitefish in Lake Champlain after Commercial Fishery Closure and Ecosystem Changes, North American Journal of Fisheries Management, 31:6, 1106-1115 To link to this article: http://dx.doi.org/10.1080/02755947.2011.641068

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ARTICLE

Lake Whitefish in Lake Champlain after Commercial Fishery Closure and Ecosystem Changes

Seth J. Herbst1 and J. Ellen Marsden* Rubenstein School of Environment and Natural Resources, University of Vermont, 81 Carrigan Drive, Burlington, Vermont 05405, USA Stephen J. Smith U.S. Fish and Wildlife Service, Lake Champlain Fish and Wildlife Resources Office, 11 Lincoln Street, Essex Junction, Vermont 05452, USA

Abstract Lake whitefish Coregonus clupeaformis were commercially fished in Lake Champlain until the 1913 fishery closure in U.S. waters. The only study of lake whitefish in the lake had been done in the 1930s. Our goals were to compare current biological parameters with historical information and to determine distribution and spatial differences in larval densities, with an emphasis on locating current spawning grounds, to gain insight on the current population in Lake Champlain. Adult lake whitefish (N = 545) were collected from 2006 to 2010 by using gill nets and trawls focused in the Main Lake. Larvae were collected extensively lakewide and intensively at Wilcox Cove and Rockwell Bay with an net. Population attributes (size, age, and sex composition; and growth, condition, and mortality) were typical of unexploited populations, as there was a wide range of length-classes (126–638 mm total length) and age-classes (1–26 years). Lake whitefish from the Main Lake had a high condition factor, and growth parameters were comparable with those of fish collected in the 1930s. Lake Champlain lake whitefish had greater asymptotic lengths than generally documented for the species. Larvae were found at sites throughout the Main Lake, and larval densities were among the highest recorded for the species (maximum = 2,558 larvae/1,000 m3); however, no lake whitefish were collected on the two historically documented spawning grounds. Lake whitefish in the Main Lake demonstrate characteristics of an unexploited population; however, evidence of spawning is absent or rare in portions of their historic range where habitat has been altered. Downloaded by [J. Ellen Marsden] at 07:04 28 December 2011 Historically, Lake Champlain supported a commercial shore- quently weigh 3.6 kg, sometimes reaching 5.4 kg (Halnon 1963). line seine fishery in the fall, focused in and near Missisquoi Bay In the early 1900s, concerns arose regarding overexploitation of in the north and Larabee’s Point in the south. Overall harvest lake whitefish. Fishermen and legislators at the time expressed and license sales peaked from 1895 to 1912. Lake whitefish the opinion that the state of Vermont would obtain greater eco- Coregonus clupeaformis were an important part of that com- nomic benefits from a strictly recreational fishery. Vermont and mercial fishery and were harvested with shoreline seines during New York prohibited seining in 1885, but Vermont reopened the fall spawning season. Annually, 41–95 fall seining licenses the fishery in 1892; the commercial harvest was closed in were issued; the highest lake whitefish yield was 31,751 kg in Vermont waters in 1913 (Wakeham and Rathbun 1897; 1912, with an average annual lake whitefish yield of 18,537 Halnon 1963; Marsden and Langdon, in press). The Quebec´ lake kg/year (Halnon 1963). Lake whitefish were reported to fre- whitefish fishery in Missisquoi Bay continued, however, despite

*Corresponding author: [email protected] 1Present address: Department of Fisheries and Wildlife, Michigan State University, 13 Natural Resources Building, East Lansing, Michigan 48824-1222, USA. Received February 22, 2011; accepted August 24, 2011

1106 LAKE WHITEFISH IN LAKE CHAMPLAIN 1107

substantial decreases in harvest and the number of licenses ters. Specifically, our objectives were to (1) determine where through time, with only four licensed fishermen harvesting a lake whitefish are currently spawning in Lake Champlain and total of 35 kg in 2004. In 2005, Quebec´ fishermen voluntarily whether changes have occurred in lake whitefish use of historic ceased seining because the high effort associated with netting spawning grounds; (2) quantify larval densities and distribution did not justify the limited harvest (K. Miller, retired commercial during emergence in the spring; (3) quantify size, age, sex com- fisherman, personal communication). position, growth, condition, and mortality and compare our data Since the closure of the commercial lake whitefish fishery with information collected in the 1930s from the two commer- in U.S. waters of Lake Champlain in 1913, only one study cially harvested locations; and (4) examine potential threats to has focused on lake whitefish. In the early 1930s, Van Oosten lake whitefish population health. Spawning grounds were iden- and Deason (1939) described the age structure, size structure, tified by lakewide sampling of larvae; current use of historic growth, and condition of lake whitefish collected in the fall and commercially harvested spawning grounds was identified of the year at the two primary commercially harvested loca- by the presence or absence of larvae. Peak larval emergence tions within the lake. In more recent years, lake whitefish have was quantified at two locations by sampling with ichthyoplank- been recorded only incidentally during biological surveys con- ton nets throughout the hatching period. We estimated growth ducted periodically from the 1930s to the late 1990s. During the parameters using the von Bertalanffy growth model, condition 1970s, a fish population inventory documented lake whitefish using the weight–length relationship, and mortality rates using in all areas of the lake except for the two historical commercial the catch curve equation; we used Fulton’s condition factor (Ful- fishing locations (Anderson 1978). The highest lake whitefish ton’s K) to compare the current condition of lake whitefish with catch rates were in the Main Lake (0.02–0.46 fish/h) and the In- the condition indicated by historical data. land Sea (0.02–0.52 fish/h in 155-m multipanel gill nets). Lake whitefish were also present in all annual gillnetting surveys from 1982 to 1998 that were associated with the assessment of lake METHODS trout Salvelinus namaycush populations before and during the Study area.—Lake Champlain is a long (200 km), narrow (19 experimental program for control of sea lampreys Petromyzon km at its widest point), and deep (19.5-m average, 122-m max- marinus (Fisheries Technical Committee 1999). imum depth) lake with a surface area of 1,130 km2. The lake is Currently, little is known about the lake whitefish population bordered by Vermont (east shoreline) and New York(west shore- in Lake Champlain. Their spawning grounds, other than those line) and by the Canadian Province of Quebec´ (north). Lake seined historically by commercial fishermen, are unknown; Champlain flows from a narrow river-like basin in the south, few to no data are available on recruitment, growth, condition, and then north to the outlet, the Richelieu River, which flows abundance, age distribution, and mortality. In the 80 years into the St. Lawrence River. Lake Champlain comprises five since the 1930 study, Lake Champlain has experienced substan- basins, separated by geographic and constructed barriers, and tial physical and biological changes. Deforestation during the varying in watershed land use (agriculture to forested), trophic 1800s, inputs from agricultural land, and shoreline development status (eutrophic to oligotrophic), fish populations (warmwa- have led to increased phosphorus loads and eutrophication, ter to coldwater species), and geology (Myer and Gruendling especially in the northern and extreme southern portions of 1979). This study focuses on four main areas, the South Lake the basin (Myer and Gruendling 1979; LCBP 2008). Exotic near Larabee’s Point, Missisquoi Bay in the north, Proctor Shoal species have been entering Lake Champlain at an increasing in the Main Lake, and the west shore of Grand Isle in the Main rate, particularly through the canal system that connects the Lake (Figure 1). Two of the study sites (Missisquoi Bay and Downloaded by [J. Ellen Marsden] at 07:04 28 December 2011 lake to the Hudson River, the Erie Canal, and the Great Lakes. Larabee’s Point) are similar in terms of physical, biological, As of 2009, 48 exotic species had colonized the lake. Of those and chemical characteristics. Both areas are shallow (<7m) invaders, the alewife Alosa pseudoharengus and zebra mussel and dominated by a warmwater fish community. Inputs of phos- Dreissena polymorpha have the highest potential to negatively phorus and sediments from surrounding land use in the last affect the lake’s native fish community (Marsden and Hauser two centuries, dominated by agriculture, have led to eutrophi- 2009; Marsden et al. 2010); the quagga mussel D. bugensis cation of these sections of the lake. The Main Lake, on the other has not yet invaded the lake. The management goal for lake hand, is primarily deep and oligotrophic, supporting warm- and whitefish in Lake Champlain is to have multiple spawning coldwater fish species; it has been less influenced by riparian populations, including those in historical spawning areas that inputs of phosphorus, contaminants, and sediment (Myer and still contain suitable habitat (Marsden et al. 2010); however, Gruendling 1979; LCBP 2008). there are no plans to reopen any commercial fishing in the lake. Fish collections.—Larval lake whitefish were sampled in To address this and other management goals, an analysis of the 2008–2010 lakewide from ice-out until catches declined to zero; current status of the species is needed. this period began as early as 14 April and extended to the first Our goal was to describe the population status of an un- week in June. Larvae were collected during the day using an studied lake whitefish population in Lake Champlain almost a ichthyoplankton net (75-cm-diameter opening, 600-µm mesh) century after the closure of the commercial fishery in U.S. wa- towed on the surface behind a boat at approximately 3.5 km/h 1108 HERBST ET AL.

sunset. Larval densities were compared among the three time periods by using a one-way analysis of variance (ANOVA). Juvenile and adult lake whitefish were sampled in the fall of 2006–2008 and year-round during 2009–2010 in the Main Lake near Proctor Shoal (Figure 1). Adult fish were also sampled in Missisquoi Bay and Larabee’s Point in the spring and fall of 2009. Lake whitefish were collected using a 7.6-m semiballoon otter trawl with a 6.4-mm stretched-mesh end liner and a chain attached to the footrope, primarily targeting juveniles; bottom-set gill nets were used to capture adults. We used three different gill nets, all 1.8 m deep, 70.6–152.4 m long, and includ- ing panels of 7.6-, 8.9-, 10.2-, 11.4-, 12.7-, 14.0-, and 15.2-cm monofilament stretch mesh. Nets were set overnight early in the study, when we were seeking locations where lake whitefish could be reliably caught, or for 2–3 h at dusk or dawn to col- lect diet data for a related study; therefore, we did not obtain CPUE data comparable with findings at other lakes. Lake white- fish were weighed (nearest g), measured (total length [TL] ± 1 mm), and examined internally to identify sex. A scale sample was taken from above the , and were extracted and stored in labeled envelopes for age estimation by means of a combination of sectioning and crack-and-burn methods (Herbst and Marsden 2011). Growth and condition.—Growth was estimated by fitting the von Bertalanffy growth model to mean length-at-age data to es- timate growth model parameters (L∞ = asymptotic length, K = growth coefficient, and t0 = theoretical age at a length of zero; FIGURE 1. Map of Lake Champlain, with enlarged areas showing study sites. t0 was estimated freely) for all lake whitefish collected from Adult lake whitefish were sampled in Missisquoi Bay (North Lake), the Main the Main Lake during 2006 to 2010 (Ricker 1975). age Lake (Proctor Shoal [PS] and Shelburne Bay), and South Lake (Larabee’s Point estimates were used for all lake whitefish collected during 2006 [LP]). Larval sampling was conducted lakewide, but focused sampling was done only in Main Lake (Wilcox Cove [WC] and Rockwell Bay [RB]). [Figure to 2010 combined, because otoliths were found to be the least available in color online.] biased and most precise of three aging structures examined for lake whitefish in Lake Champlain (Herbst and Marsden 2011), for 10 min/sample; sampling was focused near shore at 2–4-m similar to other stocks (e.g., Barnes and Power 1984; Muir et al. water depths. Samples were placed in 70% ethanol at the field 2008). Growth parameters from the von Bertalanffy model were site and taken to the laboratory for measurement and identi- estimated separately for each sex (full model) and for both sexes fication. Identification of larval lake whitefish was confirmed combined (reduced model). For this analysis, all juvenile (ages by using Auer’s (1982) key. Larval lake whitefish catches were 1–3) lake whitefish of unknown sex were added to the data set Downloaded by [J. Ellen Marsden] at 07:04 28 December 2011 standardized to catch per unit effort (CPUE) and reported as for both sexes to avoid biased estimates for K and L∞.Differ- larvae/1,000 m3. Intensive sampling (three tows once per week ences in growth between sexes were tested by using likelihood from mid-April to early June in 2008 and 2009) was done in ratio tests (Kimura 1980). Rockwell Bay and Wilcox Cove (Figure 1) to quantify temporal Growth was also estimated for lake whitefish collected in changes in larval densities. Mean densities at these sites were 2009 using scale age estimates to compare with historic data calculated for each day of sampling and then averaged across all based on scales from lake whitefish in Missisquoi Bay and days of sampling. Extensive sampling (single tows during mid- Larabee’s Point (Van Oosten and Deason 1939). Historic mean April to early June) was done lakewide in 2008 and 2009 to standard length (SL; mm) data were converted to TL (mm) using determine presence or absence of larvae and distribution of lake a conversion factor (TL = SL × 1.18) developed for Lake Cham- whitefish spawning grounds. Offshore larval sampling (from 0.5 plain lake whitefish (Van Oosten and Deason 1939). Differences km to approximately 4 km from shore, from the surface to depths in growth between all pairwise combinations of locations (Mis- of 20–60 m) was conducted in mid-May 2010, west of Wilcox sisquoi Bay, Main Lake, and Larabee’s Point) were tested using Cove and Rockwell Bay. Additional sampling was conducted likelihood ratio tests (Kimura 1980). Growth parameters from at Wilcox Cove in 2008 to determine whether larval concentra- the von Bertalanffy model were estimated separately for each tions varied at different times of the day; triplicate samples were location (full model; e.g., Missisquoi Bay) and for each pair of collected on one date during the day, at dusk, and an hour after locations (reduced model; e.g., Missisquoi Bay and Main Lake). LAKE WHITEFISH IN LAKE CHAMPLAIN 1109

Residual sums of squares were then compared for the full and reduced models by use of a likelihood ratio test. The full model was accepted if the residual sums of squares was significantly different (P ≤ 0.05) from that of the reduced model; otherwise, the reduced model was accepted, and the growth parameters for combined locations were used. Lake whitefish condition was estimated from individuals col- lected in the fall (September–October) using Fulton’s K (Ricker 1975) for comparison with values estimated for each sex from lake whitefish collected during the fall in 1930 and 1931 (Van Oosten and Deason 1939). This technique was used for historical comparison because the original weight–length data from Van Oosten and Deason (1939) were not available. Instead, historic condition was reported only as mean Fulton’s K by sex using SL (mm), so to make this comparison, we converted our data for TL to SL (SL = TL × 0.845; Van Oosten and Deason 1939). Dif- ferences in body condition, by sex, of individuals collected from 2006 to 2010 in the Main Lake and during the 1930s at the two historic locations (Missisquoi Bay and Larabee’s Point) were examined using the 95% confidence intervals (CIs) from Main Lake fish to determine whether condition values overlapped. Using TL data collected by the Vermont Fish and Wildlife Department (VTFWD) during summer (June through August) assessment of the experimental sea lamprey control program, we calculated Fulton’s K for lake whitefish between 1982 and 1997 (Fisheries Technical Committee 1999; Marsden et al. 2003). Only lake whitefish collected in the Main Lake were used for comparison with lake whitefish collected during this study; lake FIGURE 2. Larval lake whitefish sampling locations in Lake Champlain, 2008–2010 (presence = solid circle; absence = cross). Intensive sampling loca- whitefish smaller than 350 mm were excluded from the data tions (Wilcox Cove and Rockwell Bay) and locations of special concern (Mis- set to minimize the length bias associated with Fulton’s K. sisquoi Bay and Larabee’s Point) are enlarged, showing the maximum average Rennie and Verdon (2008) determined that Fulton’s K was size- ( ± SD) larval densities. The number of sample days is given in parentheses for dependent; hence, given the low numbers of smaller individuals each year; 3–12 samples were taken on each sampling date. in the 1982 to 1997 surveys, we limited potential bias by exam- ining condition of similar-sized individuals. A linear model was fit to the annual data from 1982 to 2010; because there was an Sea they were found in very low numbers and at only one loca- apparent discontinuity in the data, separate regressions were fit tion (Figure 2). Larval lake whitefish were also sparse in samples to the periods 1982–1997 and 2006–2010. from the historical commercial fishing location, Larabee’s Point, Mortality.—Mortality rates were estimated for lake whitefish with a maximum daily average density of 5 larvae/1,000 m3 from Downloaded by [J. Ellen Marsden] at 07:04 28 December 2011 collected in the Main Lake during 2006–2010 by using catch nine sample days, 2008–2010 (Figure 2). In contrast, the maxi- curve analysis (Ricker 1975). To determine the age at which mum daily average at Wilcox Cove was 2,558 larvae/1,000 m3. fish were fully recruited, we visually examined the histogram Larval tows in Missisquoi Bay, the other historical commercial of natural logarithm of catch with age and chose the age that fishing location, yielded no lake whitefish larvae in any of the corresponded to the peak leading to the descending limb of the three sampling years (Figure 2). The highest densities of larval distribution. We loge transformed the catch curve equation to lake whitefish were associated with shoreline habitats consist- estimate the instantaneous total mortality rate (Z) using linear ing of cobble or gravel ; few to no larvae were found regression, and we then calculated the annual mortality rate (A; in areas with wetland characteristics (highly organic substrate Ricker 1975). and high macrophyte densities). Larval lake whitefish were also present in all exploratory offshore samples (range per sample = 3 RESULTS 12–257 larvae/1,000 m ). At Wilcox Cove, significantly more larvae were collected at dusk (mean ± SD = 1,583 ± 896 Larval Collections larvae/1,000 m3) than at night (218 ± 52 larvae/1,000 m3; P = In 2008–2009, larval lake whitefish were distributed through- 0.02), but there was no significant difference between densities out the Main Lake (Figure 2). Larval lake whitefish were present during the day (961 ± 357 larvae/1,000 m3) and either dusk or at all locations sampled within the Main Lake, but in the Inland nighttime. 1110 HERBST ET AL.

FIGURE 3. Larval lake whitefish densities (mean [ ± SD] number of lar- vae/1,000 m3) sampled during 2009 at Rockwell Bay (upper panel) and Wilcox FIGURE 4. Lake whitefish (A) length frequency (n = 545 fish) and (B) Cove (lower panel), Lake Champlain. age frequency (n = 542 fish) in collections from Lake Champlain, 2006– 2010. Intensive larval sampling conducted at Wilcox Cove and Rockwell Bay during 2009 captured peak larval emergence of 301 mm (SE = 11.20, range = 126–511 mm) and a mean densities of 2,558 and 2,244 larvae/1,000 m3, respectively total weight of 377 g (SE = 40, range = 14–1,540 g). Overall, (Figure 3). Larval emergence at the two locations began to lake whitefish captured in both gears had a mean TL of 467 mm rapidly increase on approximately 8 May 2009, which corre- (SE = 4.51, range = 126–658 mm; Figure 4) and a mean total sponded to water temperatures ranging from 7.8◦Cto9.4◦C, weight of 1,256 g (SE = 30.48, range = 14–3,300 g). The sex and declined sharply after peaking at both locations. Peak den- composition, determined from 346 lake whitefish, was slightly sities were sampled on 13 May in Rockwell Cove and 19 May skewed toward females (females = 0.55; males = 0.45).

Downloaded by [J. Ellen Marsden] at 07:04 28 December 2011 in Wilcox Bay. Total length of larval lake whitefish at the two The age-frequency distribution indicates that multiple age- locations ranged from 10 mm on 22 April to 17 mm on 3 June classes were sampled in the Main Lake during 2006–2010. 2009. Based on otolith age estimates, age-groups ranged from ages 1 to 26 with a mean age of approximately 9 years (SE = 0.20; Adult Distribution, Size, Age, and Sex Composition Figure 4). The use of the bottom trawl increased our sample size In total, 545 lake whitefish were collected in gill nets and of younger individuals; of the 79 fish captured in the trawl, 70% bottom trawls conducted from 25 November 2006 through 6 were age 3 or younger. October 2010 during all seasons. Gill nets set in the Main Lake captured 464 lake whitefish (mean = 0.72 fish/h) with a mean Growth and Condition TL of 496 mm (SE = 3.47, range = 240–658 mm) and a mean Lake whitefish collected from the Main Lake during 2006– total weight of 1,409 g (SE = 642, range = 100–3,300 g). Gill 2010 did not exhibit sexually dimorphic growth. Female and nets set in Missisquoi Bay captured nine lake whitefish (mean = male growth parameters based on mean length at otolith age did 0.19 fish/h), all of which were collected at the southern entrance not differ significantly (P = 0.23). Combined sexes achieved L∞ to the bay in November 2010. No lake whitefish were collected of 600 mm TL and a growth coefficient K of 0.20 (Figure 5). in 78.4 h of gillnetting at Larabee’s Point. The bottom trawl The t0 value was −0.66 with sexes combined and the inclusion captured 81 lake whitefish (mean = 6.2fish/h)withameanTL of younger individuals (ages 1 and 2) of unknown sex. LAKE WHITEFISH IN LAKE CHAMPLAIN 1111

FIGURE 5. Predicted mean ( ± SD) total length (mm) at age (years) based on ± K the von Bertalanffy growth model for all lake whitefish collected in Lake Cham- FIGURE 6. Annual mean ( SD) Fulton’s condition factor (Fulton’s )for plain during 2006–2010. Estimated von Bertalanffy growth model parameters 356 lake whitefish collected between 1982 and 1997 in Lake Champlain (Main Lake) by the Vermont Fish and Wildlife Department and for 449 lake whitefish (asymptotic length L∞ and growth coefficient K) and sample size (N) for all fish (including those of unknown sex) are shown. collected in the Main Lake and near Grand Isle during the present study (2006– 2010). Only fish having a total length of at least 350 mm were used in the calculation of mean Fulton’s K. Lake whitefish growth estimated from scales of a subset of 219 individuals collected from the Main Lake during 2009 higher than that of Missisquoi Bay fish (Fulton’s K = 1.62; N was not significantly different from historic growth estimated = 61). Condition calculated from TL showed the same pattern, from 175 fish sampled at Larabee’s Point (P = 0.06) or 120 with females having higher condition (Fulton’s K = 1.13) than fish sampled at Missisquoi Bay (P = 0.147). Missisquoi Bay males (Fulton’s K = 1.05). and Larabee’s Point lake whitefish had significantly different Annual mean Fulton’s K calculated from TL averaged 1.2 growth parameters (P = 0.012; Van Oosten and Deason 1939). ± 0.14 during the 1980s and 1990s and 1.1 ± 0.13 during this Missisquoi Bay lake whitefish collected in 1930 attained the study. The decline in annual mean Fulton’s K from 1982 to 2010 largest L∞ (635 mm) compared with Larabee’s Point (L∞ = was significant (F = 230.2; df = 1, 805; P ≤ 0.0001). Despite 607 mm) and our Main Lake fish (L∞ = 605 mm). Growth a decline in the 1990s, the slope of the annual mean Fulton’s K coefficient K decreased from south (Larabee’s Point: 0.28) to for the 1982–1997 period was not significantly different from north (Missisquoi Bay: 0.21); our centrally located Main Lake zero (F = 0.069; df = 1, 356; P < 0.79), whereas condition site had an intermediate value (0.24). declined significantly during this study period (F = 52.7; df = Body condition of lake whitefish in Main Lake estimated 1, 447; P ≤ 0.0001; Figure 6). This analysis is partly confounded using Fulton’s K was significantly higher than for lake white- by the fact that lake whitefish in 2006–2008 were collected in fish collected from Missisquoi Bay in 1930 for both sexes but Grand Isle only in fall, whereas all other fish were collected in was not significantly different from that for fish captured at the Main Lake during summer (1982–1997) or during spring, Larabee’s Point in 1931 based on the 95% CIs. This comparison summer, and fall (2009–2010). Downloaded by [J. Ellen Marsden] at 07:04 28 December 2011 with historic data included only the 170 lake whitefish collected from the Main Lake in the fall of 2006–2010; no lake whitefish Mortality had been collected during fall in prior studies. Females in our Mortality rates were estimated for age-6 and older lake white- study accounted for 60% of the total Main Lake sample size fish collected from the Main Lake in 2006–2010; based on the and had a greater mean SL (453 mm; N = 102; SE = 4.49) age-frequency histogram, lake whitefish were fully recruited to than males (444 mm; N = 68; SE = 5.32). Female lake white- our gear by age 6 (Figure 3). The Z for lake whitefish of ages = fish condition (Fulton’s K = 1.87; 95% CI = 1.83–1.91) was 6 to 26 was estimated at 0.24 (95% CI 0.19–0.29), A was = significantly higher than the condition of males (Fulton’s K = 0.21 (95% CI 0.17–0.24), and annual survival rate (S)was = 1.74; 95% CI = 1.68–1.78) based on 95% CI for fish collected 0.79 (95% CI 0.75–0.83). Given the absence of a commercial in the Main Lake. Condition of females from the Main Lake fishery and an extremely limited sport harvest, A approximates was similar to that of females from Larabee’s Point (Fulton’s K natural mortality for lake whitefish in Lake Champlain. = 1.84; N = 77), and Fulton’s K-values of fish sampled at both locations were higher than those of fish sampled at Missisquoi DISCUSSION Bay (Fulton’s K = 1.69; N = 59). The same pattern held true for Lake whitefish in Lake Champlain currently have biolog- males; condition in the Main Lake was similar to that of fish in ical attributes characteristic of a stable, unexploited popula- Larabee’s Point (Fulton’s K = 1.71; N = 98) and significantly tion. Lake whitefish in 2006–2010 were represented by multiple 1112 HERBST ET AL.

age-classes and a wide distribution of lengths, with slow growth has not been severely altered. Adult lake whitefish were sam- and low mortality rates. Larval densities were high throughout pled in this basin during gill-net surveys by the VTFWD in the Main Lake. While data are not available from the period 1978 (0.4–0.52 fish/net-hour) and 1993–1996 (Anderson 1978; of exploitation, the current population parameters are similar Fisheries Technical Committee 1999), so spawning in this basin to those recorded in a study in the 1930s: Lake whitefish from may occur in the northern section, where we did not sample. the Main Lake had growth parameters and mean Fulton’s K- Larval densities elsewhere in Lake Champlain are among the values similar to those of lake whitefish from Larabee’s Point highest reported for the species. For perspective, average maxi- and Missisquoi Bay in 1930–1931, though Main Lake fish had a mum larval densities in Wilcox Cove and Rockwell Bay (2,558 greater condition value than fish from Missisquoi Bay. The only and 2,244 larvae/1,000 m3) were substantially higher than those apparent cause for concern is the low or absent larval densities in Chaumont Bay, Lake Ontario (469 larvae/1,000 m3), and at historic commercial fishing sites. sites throughout Lake Michigan (4–1,922 larvae/1,000 m3)but Before this study, knowledge of lake whitefish spawning were lower than those in Green Bay, Lake Michigan (3,756 lar- grounds in Lake Champlain was limited to historical informa- vae/1,000 m3; Hoagman 1973; Freeburg et al. 1990; Mckenna tional regarding the fall shoreline seining fishery, which har- and Johnson 2009; Claramunt et al. 2010). Wilcox Cove and vested lake whitefish in the northern portions of the lake when Rockwell Bay have spawning substrate suitable for lake white- the species was preparing to and near Larabee’s Point fish and are protected from wave-generated disturbances, except in the south (Marsden and Langdon, in press). Historical docu- for those from the west, which can affect egg survival rates and ments do not indicate why other areas were not fished; we found recruitment. that shorelines throughout much of the Main Lake consist of Most studies focus on larval lake whitefish sampling near gravel and cobble, which are suitable and preferred spawning shore during the day, as larvae are concentrated at the surface substrates for lake whitefish (Begout´ Anras et al. 1999). We at- in shallow depths (<3 m) and are seldom captured over adja- tempted to identify spawning areas by gillnetting for spawning cent deep water further from shore after hatching (Hart 1930; fish in fall but found spent females on only one date, 20 De- Hoagman 1973). Hoagman (1973), for example, captured few cember 2006; interestingly, Smith (1914) concluded that lake to no larvae in Green Bay, Lake Michigan, at sites 100–150 m whitefish spawn after ice formation. Sampling for larval lake from shore at depths greater than 10 m. In contrast, we collected whitefish showed that they were present at all sites with suitable mean daily maximum densities of 171 larvae/1,000 m3 at the substrate. Larvae found in the Main Lake could not have drifted surface over depths ranging from 26 to 61 m, relative to the 969 from Missisquoi Bay, as more than 25 km and several islands larvae/1,000 m3 captured nearshore on 12 May 2010. These off- and causeways separate the bay and the northernmost of our shore larvae were presumably displaced from nearshore areas sampling sites (Figure 1). Thus, we assume that the paucity of by currents or offshore winds. The frequency and magnitude of commercial fishing in the Main Lake was due to preferences this offshore advection are unknown, as is the survival potential of fishers for fishing access rather than absence of spawning for these larvae. Offshore movements of larvae may be more aggregations. common than generally realized, given that sampling is usu- The current scarcity or absence of larval lake whitefish in ally not extended to offshore areas. We collected significantly Missisquoi Bay and Larabee’s Point and the low catches of higher larval densities at dusk than at night; daytime densities adults at these sites in the fall may indicate that (1) local pop- were lower than at dusk, but high variability and a low number ulations were lost due to exploitation; (2) populations found in of replicates precluded finding a significant difference. Assump- these areas historically were only staging rather than spawn- tions about higher concentrations of larvae at the surface during Downloaded by [J. Ellen Marsden] at 07:04 28 December 2011 ing; or (3) spawning substrates have been degraded. Given that the day than at nighttime may be incorrect; Hoagman (1973), Van Oosten and Deason (1939) collected large numbers of lake for example, reported higher larval catches during the night than whitefish in fall seines during 1930 and 1931, 18 years after during the day. commercial harvest ended, overexploitation does not appear to Given the high larval densities throughout most of the lake, be the problem. Missisquoi Bay is connected to the rest of Lake indicative of good reproductive output, are recruitment, growth, Champlain by a narrow passage, so it seems unlikely that lake and survival robust? Lake whitefish in Lake Champlain had whitefish would move to a cul-de-sac area to stage before spawn- a wide size range with multiple length modes, and multiple ing elsewhere. Thus, habitat degradation may be an important age-classes, similar to unexploited populations from several factor in these areas. As a result of anthropogenic changes in Canadian lakes (Johnson 1976; Mills et al. 2005). In contrast, land use in the last century, Missisquoi Bay and the South Lake exploited lake whitefish populations are characterized by low are now highly eutrophic, having high densities of macrophytes, numbers of older individuals and, depending on density effects, silt, and other organic matter that limit available oxygen needed smaller individuals. for egg survival (Myer and Gruendling 1979; LCBP 2008). Growth of lake whitefish from Lake Champlain was not sex- Similar changes have been shown to negatively influence lake ually dimorphic, which was unexpected because lake whitefish whitefish recruitment in other systems (Evans et al. 1996). The growth frequently differs by sex in both unexploited and ex- Inland Sea, where larval lake whitefish were also rare (N = 1), ploited lakes (Beauchamp et al. 2004; Cook et al. 2005; Hosack LAKE WHITEFISH IN LAKE CHAMPLAIN 1113

2007). Lake whitefish from Lake Champlain had an L∞ value in the 1980s and 1990s, Fulton’s K was robust throughout this greater than those of the exploited lake whitefish populations in period and a large number of year-classes of lake whitefish are the Great Lakes and in 28 inland lakes (Beauchamp et al. 2004) currently present. Average Fulton’s K during the current study and greater than those of unexploited populations in Lake Pend was lower than in the 1980s and 1990s; mean annual Fulton’s K Oreille (Hosack 2007); only lake whitefish from Lake Superior’s declined during the 1990s and 5-year period of the study. How- Apostle Island region had a larger L∞ (M. J. Seider and S. T. ever, annual means in the 1990s were based on small sample Schram, Wisconsin Department of Natural Resources, unpub- sizes (6–20 fish), and predictions about the trajectory of lake lished data). Growth coefficients K for fish in Lake Champlain whitefish populations in the lake based on this short time period were greater than those of fish from Lake Pend Oreille (females: and relatively small decline may be premature. 0.13; males: 0.15; Hosack 2007) but similar to those of most Lake whitefish from Lake Champlain have been exposed to other lake whitefish populations. Lake Erie males had a growth very little exploitation since the closure of the commercial fish- coefficient of 0.32, which was among the highest reported; other ery in U.S. waters in 1912, which explains the high S of 79%, growth coefficients ranged from 0.22 to 0.31 for Lake Erie fe- typical for unexploited populations. Mortality estimates from males, 28 inland lakes populations, and 22 Great Lakes stocks catch-curve analysis involve assumptions of consistent recruit- (Beauchamp et al. 2004; Cook et al. 2005). Changes in lake ment and constant mortality over all ages and over time. These whitefish growth have been related to density-dependent fac- assumptions are likely to be violated in any natural popula- tors, with slow growth in years of increased abundance and tion. Mortality in Lake Champlain is largely a consequence of biomass (Healey 1980; Wright and Ebener 2005). Abundance stresses imposed by sea lamprey wounding, maturation, spawn- and biomass of lake whitefish in Lake Champlain are unknown, ing, and senescence, as mortality from fishing is virtually ab- but given the high L∞ and slow growth rates, we speculate sent. We do not have estimates of sea lamprey-induced mortality that density-dependent factors are not limiting growth in Lake for lake whitefish; however, sea lampreys in Lake Champlain Champlain lake whitefish. are smaller, and their attacks on are less lethal, than Lake whitefish densities in Lake Champlain do not seem in the Great Lakes (Madenjian et al. 2008), which suggests to be hindering the population’s ability to find available food that sea lamprey-induced mortality of lake whitefish may also resources for somatic growth or reproduction. After the intro- be lower than in the Great Lakes. With no more than 3 years duction of zebra mussels to Lake Champlain in 1993 (Marsden of larval sampling at any one site, no data for postlarval lake and Hauser 2009), we anticipated a diet shift from native prey whitefish, and low numbers of juveniles, we do not have suf- to these less energetically valuable exotic mussels, as was seen ficient data to evaluate recruitment variability. Moreover, no in the Great Lakes (Mohr and Nalepa 2005). In the Great Lakes, dominant year-class was found that could be tracked over the this diet shift negatively impacted growth and condition, changes years of the study to evaluate survival. Acquisition of these data that ultimately affect the reproductive capabilities of a fish pop- should be a priority for long-term evaluation of lake whitefish ulation; however, because of the growth and condition values in survival. Lake Champlain lake whitefish, we do not anticipate that similar Van Oosten and Deason (1939) concluded that Missisquoi dietary shifts have occurred in Lake Champlain subsequent to Bay and Larabee’s Point had separate lake whitefish popula- the introduction of zebra mussels. tions, on the basis of the biological attributes of the fish they Lake whitefish in Lake Champlain have maintained good collected in the 1930s. However, both of these areas are shallow condition and high survival despite high wounding rates by and too thermally restrictive to support lake whitefish in the sea lampreys. The energetic cost of sea lamprey parasitism is summer; they must have been used by lake whitefish only for Downloaded by [J. Ellen Marsden] at 07:04 28 December 2011 generally associated with poor condition, low fecundity, and spawning and early larval growth. The virtual absence of lar- high mortality rates; for example, commercial landings of lake vae and adults in these locations during our study suggests that whitefish in Lakes Huron, Michigan, and Superior declined dur- lake whitefish spawning is now minimal or absent in Missisquoi ing periods of high sea lamprey abundance and rose after con- Bay and Larabee’s Point. VanDeHey et al. (2009) found that trol was implemented (Smith and Tibbles 1980; Spangler and lake whitefish in Lake Michigan have small home ranges and Collins 1980). In regions of Lake Superior, where sea lamprey genetically differentiated subpopulations; if similar population populations have been controlled for several decades, wounding substructuring was historically present in Lake Champlain, then on lake whitefish averages 0.06–1.0 wounds per 100 fish (Har- habitat changes may have eliminated the northern and southern vey et al. 2008). In contrast, lake whitefish in Lake Champlain spawning populations. had an average of 10.7 ± 7.5 wounds per 100 fish in the 11 Our data indicate that discrete spawning stocks of lake white- years preceding the beginning of the experimental control pe- fish have potentially been extirpated from the two commercially riod (1980–1990), dropping to an average of 7.3 ± 4.5 wounds fished locations of Lake Champlain, probably as a result of his- per 100 fish during the experimental control period (1991–1997; torical changes in riparian land use and increased inputs of Fisheries Technical Committee 1999). In the current study, con- phosphorus. High sediment loads and eutrophication in Mis- ducted during full implementation of sea lamprey control, there sisquoi Bay and Larabee’s Point may have made these sites un- were 2.0 wounds per 100 fish. Despite the high wounding rates suitable for lake whitefish spawning. Commercial fishing could 1114 HERBST ET AL.

also have contributed to the decline in Missisquoi Bay, where Harvey, C. J., M. P. Ebener, and C. K. White. 2008. Spatial and ontogenetic harvest continued until the mid-2000s and commercial catches variability of sea lamprey diets in Lake Superior. Journal of Great Lakes of lake whitefish declined steadily since the 1960s (Marsden Research 34:434–449. Healey, M. C. 1980. Growth and recruitment in experimentally exploited lake and Langdon, in press), but the Larabee’s Point population has whitefish (Coregonus clupeaformis) populations. Canadian Journal of Fish- not been harvested since the fishery closed in 1914. In the Main eries and Aquatic Sciences 37:255–267. Lake, in contrast, suitable spawning substrate is readily avail- Herbst, S. J., and J. E. Marsden. 2011. Comparison of precision and bias of able, larval production is high, and the adult population metrics scale, fin ray, and otolith age estimates for lake whitefish in Lake Champlain. are robust and appear to be healthy. Journal of Great Lakes Research 37:386–389. Hoagman, W. J. 1973. The hatching, distribution, abundance, growth, and food of the larval lake whitefish (Coregonus clupeaformis Mitchill) of central Green Bay, Lake Michigan. Institute of Freshwater Research Drottningholm ACKNOWLEDGMENTS 53:1–20. We thank Shawn Good (VTFWD) for access to labora- Hosack, M. A. 2007. Population dynamics of lake whitefish in Lake Pend tory equipment. We also thank Elias Rosenblatt, Neil Thomp- Oreille, Idaho. Master’s thesis. College of Natural Resources, University of Wisconsin-Stevens Point, Stevens Point. son, Josh Ashline, Kevin Osantowski, Lindsay Schwarting, and Johnson, L. 1976. Ecology of Arctic populations of lake trout, Salvelinus na- Joanna Hatt for assistance in the field and laboratory, and maycush, lake whitefish, Coregonus clupeaformis, , S. alpinus,and Richard Furbush, Joe Bartlett, and Rebecca Gorney for as- associated species in unexploited lakes of the Canadian Northwest Territories. sistance with fish collection. We especially thank the Na- Journal of the Fisheries Research Board of Canada 33:2459–2488. tional Oceanic and Atmospheric Administration for funding this Kimura, D. K. 1980. Likelihood methods for the von Bertalanffy growth curve. U.S. National Marine Fisheries Service Fishery Bulletin 77:765– project. 776. LCBP (Lake Champlain Basin Program). 2008. State of the lake and ecosystem indicators report – 2008. LCBP, Grand Isle, Vermont. REFERENCES Madenjian, C. P., B. D. Chipman, and J. E. Marsden. 2008. Estimate of lethal- Anderson, J. K. 1978. Lake Champlain fish population inventory, 1971–1977. ity of sea lamprey attacks in Lake Champlain: implications for fisheries Vermont Fish and Wildlife Department, Essex Junction. management. Canadian Journal of Fisheries and Aquatic Sciences 65:535– Auer, N. A. 1982. Identification of larval fishes of the Great Lakes basin with 542. emphasis on the Lake Michigan drainage. Great Lakes Fishery Commission, Marsden, J. E., B. D. Chipman, L. J. Nashett, J. K. Anderson, W. Bouffard, Special Publication 82-3, Ann Arbor, Michigan. L. E. Durfey, J. E. Gersmehl, W. F. Schoch, N. R. Staats, and A. Zerren- Barnes, M. A., and G. Power. 1984. A comparison of otolith and scale ages for ner. 2003. Evaluation of the eight-year sea lamprey control program on western Labrador lake whitefish, Coregonus clupeaformis. Environmental Lake Champlain. Journal of Great Lakes Research 29(supplement 1):655– Biology of 10:297–299. 676. Beauchamp, K. C., N. C. Collins, and B. A. Henderson. 2004. Covariation of Marsden, J. E., B. D. Chipman, B. Pientka, W. F. Schoch, and B. A. Young. growth and maturation of lake whitefish (Coregonus clupeaformis). Journal 2010. Strategic plan for Lake Champlain fisheries. Great Lakes Fishery Com- of Great Lakes Research 30:451–460. mission, Miscellaneous Publication 2010-03, Ann Arbor, Michigan. Begout´ Anras, M. L., P. M. Cooley, R. A. Bodaly, L. Anras, and R. J. P. Marsden, J. E., and M. Hauser. 2009. Exotic species in Lake Champlain. Journal Fudge. 1999. Movement and habitat use by lake whitefish during spawning of Great Lakes Research 35:250–265. in a boreal lake: integrating acoustic telemetry and geographic information Marsden, J. E., and R. Langdon. In press. The history and future of Lake systems. Transactions of the American Fisheries Society 128:939–952. Champlain’s fishes and fisheries. Journal of Great Lakes Research. Claramunt, R. M., A. M. Muir, T. M. Sutton, P. J. Peeters, M. P. Ebener, J. D. McKenna, J. E., Jr., and J. H. Johnson. 2009. Spatial and temporal variation in Fitzsimons, and M. A. Koops. 2010. Measures of larval lake whitefish length distribution of larval lake whitefish in eastern Lake Ontario: signs of recovery? and abundance as early predictors of year-class strength in Lake Michigan. Journal of Great Lakes Research 35:94–100. Journal of Great Lakes Research 36:84–91. Mills, K. H., E. C. Gyselman, S. M. Chalanchuk, and D. J. Allan. 2005. The

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