Lake Whitefish Research Articles

Using climate and a minimum set of local characteristics to predict the future distributions of freshwater fish in Ontario, Canada, at the lake-scale

Aim:In order to overcome data limitations on predicting future distributions of freshwater fishes at the lake scale, our aim was to build simple species distribution models for three focal fishes from warm-, cool- and cold-water guilds, using a small set of local environmental variables paired with climate information. Location:A total of 6715 inland freshwater lakes across Ontario, Canada. Methods:Multiple logistic regression techniques were employed to model historical species occurrence with seven candidate local environmental variables, including a climate index. Model accuracy was tested by: (i) validating with a subset of the historical dataset (centered around the 1970s), and (ii) predicting species occurrence in lakes using a contemporary dataset (centered around the 2000s), representing ∼30 years of climatic change. Projected climate data was then used to model species occurrence into the 2041–2070 time period. Results:The models for each thermal guild performed well (average AUC of 0.79) using the historical validation dataset as well as the contemporary dataset. The final set of predictors was unique to each species; however lake surface area, and the climate index were significant in all models. In all three models, the climate index was the most influential variable. Cold-water lake whitefish and cool-water walleye are predicted to be lost from a large number of lakes (1283 and 1792, respectively) by 2041–2070 across central and southern Ontario. Nevertheless, numerous hospitable lakes will be available to both fishes in Ontario’s far north (OFN), where 108 lakes are predicted to be suitable for lake whitefish and 247 are predicted to be suitable for walleye. Thousands of lakes across Ontario are predicted to be hospitable for rock bass in the future, including 35 locations in OFN. Main Conclusions:Modified logistic regression models, incorporating a minimum of local environmental and climate information, show promise in predicting the future distributions of fishes in Ontario lakes. This is an important first step in building conservation capacity for freshwater fishes in northern regions, where conservation value is very high, but data are particularly limited.

Tribal Commercial Fish Harvests in the Upper Laurentian Great Lakes Consistently Demonstrate Nutritional Importance Along with Risks.

Introduction: The Great Lakes Native American tribes are traditionally a fishing culture; however due to fear of fish contamination they only consume one third of the recommended fish intake. The Inter-Tribal Fisheries and Assessment Program (ITFAP) in Sault Ste. Marie, MI regularly monitors contaminant concentrations in the fillet portions of lake trout and whitefish from lakes Superior, Huron, and Michigan. A risk quantification analysis of Methylmercury (MeHg) adjusted for nutritional benefit in fish caught during the 2012, 2013, and 2014 tribal fish harvests was conducted. Methods: The Ginsberg and Toal (2009, 2015) method was used to estimate the health benefits (decreased risk of cardiovascular disease (CHD)) and neurodevelopment (predicted improved visual recall memory (VRM) of infants exposed in-utero) if each species was consumed at 6 ounces/week. The CHD model estimates the difference of 23% higher risk/1 ppm hair Hg from the 14.6% lower risk/100 mg Omega-3. The neurodevelopment model estimates the difference in -3.5 VRM points/1 ppm maternal hair Hg from t +3.04 VRM points/100 mg maternal Omega-3. These estimates were applied to the average MeHg concentrations in the ITFAP fish samples and reported Omega-3 values for each species/lake. Results: Clear benefits relative to risks were observed for both species. Predicted benefits for whitefish were +3.9 VRM points/ -22.5% CHD risk (L. Superior), +1.7 VRM points/-14.1% CHD risk (L. Michigan), and +2.2 VRM points/-16% CHD risk (L. Huron). Estimated health benefits for lake trout were: + 4.1 VRM points/-26.8% CHD risk (L. Superior), +9.0 VRM points/-49% CHD risk (L. Michigan), and +5.7 VRM points/-35.2% CHD risk (L. Huron). Discussion: This is consistent with previous findings that tribal harvests provide clear health benefits and further demonstrate the importance of traditionally-caught fish for tribal health. It also justifies culturally-responsive outreach to help navigate dietary trade-offs.

Adaptation and acclimation of traits associated with swimming capacity in Lake Whitefish (coregonus clupeaformis) ecotypes.

BackgroundImproved performance in a given ecological niche can occur through local adaptation, phenotypic plasticity, or a combination of these mechanisms. Evaluating the relative importance of these two mechanisms is needed to better understand the cause of intra specific polymorphism. In this study, we reared populations of Lake Whitefish (Coregonus clupeaformis) representing the’normal’ (benthic form) and the ‘dwarf’ (derived limnetic form) ecotypes in two different conditions (control and swim-training) to test the relative importance of adaptation and acclimation in the differentiation of traits related to swimming capacity. The dwarf whitefish is a more active swimmer than the normal ecotype, and also has a higher capacity for aerobic energy production in the swimming musculature. We hypothesized that dwarf fish would show changes in morphological and physiological traits consistent with reductions in the energetic costs of swimming and maintenance metabolism.ResultsWe found differences in traits predicted to decrease the costs of prolonged swimming and standard metabolic rate and allow for a more active lifestyle in dwarf whitefish. Dwarf whitefish evolved a more streamlined body shape, predicted to lead to a decreased drag, and a smaller brain, which may decrease their standard metabolic rate. Contrary to predictions, we also found evidence of acclimation in liver size and metabolic enzyme activities.ConclusionResults support the view that local adaptation has contributed to the genetically-based divergence of traits associated with swimming activity. Presence of post-zygotic barriers limiting gene flow between these ecotype pairs may have favoured repeated local adaptation to the limnetic niches.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0732-y) contains supplementary material, which is available to authorized users.

Incubation of lake whitefish (Coregonus clupeaformis) embryos in cooling water discharge and the impacts of fluctuating thermal regimes on development

Thermal discharges released from industrial cooling water systems represent a potential environmental risk to fish species that spawn in nearshore waters. We investigated the impacts of in situ incubation of lake whitefish (Coregonus clupeaformis) embryos in the vicinity of a nuclear generating station. Over 3 consecutive years, fertilized embryos were deployed in Lake Huron using custom-built incubation chambers coupled with data loggers to monitor water temperature. Temperatures at sites in the vicinity of the thermal discharge were significantly elevated compared with reference locations, with mean winter temperatures up to 3 °C warmer. Temperatures were also more variable at these sites, with a significantly greater daily temperature range and rate of change. Embryos developing at discharge sites were significantly larger with smaller yolks than those from the reference stations, suggesting an advanced growth. This increased growth was supported by thermal data, with discharge sites predicted to be more than 10% advanced based on growth rate modelling. These temperature changes and increase in development rate are below thresholds for embryonic mortality but could potentially impact posthatch larval survival.

Islands in the ice stream: were spawning habitats for native salmonids in the Great Lakes created by paleo‐ice streams?

AbstractLake trout Salvelinus namaycush, lake whitefish Coregonus clupeaformis and cisco Coregonus artedi are salmonid fishes native to the Laurentian Great Lakes that spawn on rocky substrates in the fall and early winter. After comparing the locations of spawning habitat for these species in the main basin of Lake Huron with surficial substrates and the hypothesized locations of fast‐flowing Late Wisconsinan paleo‐ice streams, we hypothesize that much of the spawning habitat for these species in Lake Huron is the result of deposition and erosion by paleo‐ice streams. This hypothesis may represent a new framework for the identification and protection of spawning habitat for these native species, some of which are currently rare or extirpated in some of the Great Lakes. We further suggest that paleo‐ice streams may have been responsible for the creation of native salmonid spawning habitat elsewhere in the Great Lakes and in other glaciated landscapes.

The Influence of Stock Assessment Frequency on the Achievement of Fishery Management Objectives

AbstractBecause of resource limitations with respect to both funding and staff expertise, there is growing interest among fishery management agencies in moving from annual to less‐frequent assessments of fish stocks. We conducted simulations based on Lake Whitefish Coregonus clupeaformis populations in the Laurentian Great Lakes to evaluate (1) how statistical catch‐at‐age assessment frequency, the time lag between data collection and assessment, and approaches to setting target harvests in the years between assessments affected the achievement of management objectives; and (2) how the outcomes were influenced by the quality of assessment data, features of the populations, and characteristics of the fisheries exploiting the populations. We found that as assessments became less frequent, relative yields were reduced and the risk of stock depletion and interannual variation in yield increased. The effects of less‐frequent assessments were ameliorated in populations with greater levels of productivity and when target mortality was lower. Conversely, the effects of assessment frequency were largely insensitive to changes in recruitment variation or the quality of assessment data. A 1‐year lag between data collection and assessment when assessments were conducted annually primarily affected the risk of stock depletion and the interannual variation in yield. As recruitment variation increased, relative yield also became sensitive to the 1‐year lag. Approaches to setting harvest targets in years between full assessments were less important than assessment frequency, and no single approach consistently outperformed other rules. Although populations with low productivity were the most sensitive to changes in assessment frequency and the lag between data collection and assessment, the management of those populations benefited to a greater extent from implementation of an appropriate target mortality rate than from more‐frequent assessments or removal of the 1‐year lag.Received November 18, 2015; accepted March 9, 2016 Published online July 7, 2016

Consistent differential resource use by sympatric lake (Coregonus clupeaformis) and round (Prosopium cylindraceum) whitefish in Lake Huron: a multi-time scale isotopic niche analysis

Lake (Coregonus clupeaformis) and round (Prosopium cylindraceum) whitefish are sympatric benthivores in Lake Huron that are thought to coexist via niche partitioning. However, little is known about long-term resource use and niche overlap across different temporal scales. We used a multiyear (2010–2012) and multi-tissue (liver, muscle, and bone layers) isotopic niche analysis to characterize and compare resource use by lake and round whitefish across several time scales. Lake whitefish consistently used more diverse, 13C-depleted (mean δ13C = −21.9‰) and 15N-enriched (mean δ15N = +9.3‰) resources than round whitefish (mean δ13C = −18.2‰; mean δ15N = +8.3‰). Niche overlap occurred only in liver, representing the spawning period, while niche segregation was highest in juvenile life stages. Individuals of both species made variable resource shifts among time periods, suggesting that spawning aggregations are composed of individuals representing a variety of feeding strategies and locations. Our study confirms that differential resource use is an important strategy for these fish as adults and demonstrates life-long niche partitioning beginning before age-2.

Seasonal and Diel Bathythermal Distributions of Lake Whitefish in Lake Huron: Potential Implications for Lake Trout Bycatch in Commercial Fisheries

AbstractDepths and temperatures recorded during 2003–2005 by archival tags implanted in Lake Whitefish Coregonus clupeaformis and in Great Lakes origin (GLO) and New York Finger Lakes origin (FLO) strains of Lake Trout Salvelinus namaycush were used to compare seasonal diel depth and temperature distributions in Lake Huron. Seasonal depth distributions were examined to determine if species differences could be exploited to reduce bycatch of Lake Trout in commercial Lake Whitefish gill‐net fisheries. Both GLO and FLO Lake Trout used deeper and colder waters than Lake Whitefish during daylight and dark. Temperature differences between species were greatest during periods of stratification when behavioral thermoregulation was possible. Other than during spawning periods, the greatest depth and temperature separation occurred in late July between FLO Lake Trout (37.0 m; 6.5 ºC) and Lake Whitefish (25.1 m; 10.2 ºC). If maximum depths of gill nets were regulated seasonally to between 25 and 35 m, ≥ 50% of the Lake Whitefish population would be vulnerable while avoiding 89% or more of Lake Trout. Lake Trout percentages targeted under such regulations would be lowest in late July (GLO = 8% and FLO = 11%) and early August (GLO = 4% and FLO = 7%). However, archival tags measure fish depth and not location or bottom depth, and modal depths of gill‐net effort for Lake Whitefish (38 to 57 m) exceeded those from the Lake Whitefish archival tag data. This discrepancy suggests that many Lake Whitefish might be pelagic above the reach of bottom‐set gill nets, so depth restrictions could be less effective in reducing Lake Trout bycatch than suggested by our data. A further implication is that use of gill nets suspended above the bottom to target pelagic Lake Whitefish could also reduce bycatch while potentially increasing Lake Whitefish harvest.Received August 19, 2015; accepted February 21, 2016 Published online June 28, 2016

Increased taxonomic resolution of Laurentian Great Lakes ichthyoplankton through DNA barcoding: A case study comparison against visual identification of larval fishes from Stokes Bay, Lake Huron

Ichthyoplankton can be difficult to identify due to a lack of morphological differences among closely-related species. Traditional visual identification of ichthyoplankton requires special knowledge to employ morphological keys. Accurate species-level identification is often required to support monitoring programs for those taxa that are considered valued ecosystem components in environmental assessments. DNA-based methods are gaining in popularity as an alternative to visual identification techniques, but direct comparisons of methodological performance between identification techniques are lacking. The goal of this study was to evaluate and explore the consistency between visual and DNA barcoding species-level identification methods, using a case study of larval fish caught in plankton tows at Stokes Bay, Lake Huron during the spring of 2011. Four participants served as Identifiers (3 Novice, 1 Expert) for visual identification of this multi-species set of larval fishes; including Lake Whitefish, Lake Herring, Yellow Perch, Iowa Darter, Ghost Shiner, and Rainbow Smelt. Barcoding successfully identified 51/55 (92.7%) of the larval fishes, while visual identification using a dichotomous key showed substantial variation between observers, and across family/species. There was a 93.7% consistency between visual and barcoding identification at the family level, and a 71.5% consistency level between visual and barcoding at the species level. Potential sources of error are discussed for both identification methods, leading to a recommendation for the coordinated use of both visual and barcoding identification methods to improve species-level assessments for wild ichthyoplankton samples.

Effects of changes in density-dependent growth and recruitment on sustainable harvest of lake whitefish

Abstract Substantial declines in growth and recruitment of lake whitefish ( Coregonus clupeaformis ) and changes in key density-dependent relationships since the 1990s have raised concerns about the effects of these changes on valuable commercial fisheries in Lake Huron. There is evidence for lake whitefish in the southern main basin of Lake Huron that growth and recruitment rates have been reduced by up to 50%. Using a life history model parameterized from fishery-independent survey data for lake whitefish, we investigated the effects of declines in growth and recruitment rates on population dynamics and sustainable harvest. We evaluated a baseline scenario characterized by high growth and recruitment rates, an alternative scenario with a reduced growth rate, and another alternative scenario in which both growth and recruitment rates were reduced. Yield consistently declined by at least 71% in both alternative scenarios compared to the baseline scenario. Also, fishing became unsustainable when both growth and recruitment rates were reduced and the maximum instantaneous fishing mortality rate exceeded 0.5. Our results suggest that the recent reductions in growth and recruitment observed in Lake Huron are of sufficient magnitude to alter productivity and reduce how much can be sustainability harvested from these stocks.

Fish community changes in Shoal Lake, Canada, following the overexploitation of a top predator

ABSTRACTOverexploitation of a single target species often results in fish community changes. Commercial and recreational overexploitation of walleye (Sander vitreus) in Shoal Lake, Ontario, in the early 1980s resulted in a ban on walleye fishing. In this study, we summarize potential changes in the catch-per-unit-effort of large-bodied fishes (abundance and biomass in gill nets) and small-bodied fishes (abundance in shoreline seines) for most years in the period 1979–2001. Through our analysis of gill net data, we found that the collapse of walleye was followed by increases in the abundance and biomass of yellow perch (Perca flavescens), cisco (Coregous artedi), and white sucker (Catostomus commersoni). Lake whitefish (Coregonus clupeaformis) also increased following the collapse, but this pattern was confounded by reduction in the lake whitefish commercial harvest. We found no evidence that the collapse of walleye benefited potential competitors (e.g. northern pike, Esox lucius). The collapse also resulted in semi-annual alternations between minnow (Pimaphales spp.) and a combination of yellow perch and shiners (Notropis spp.). Overall, our results are consistent with the general literature showing that the overexploitation of a top predator affects the broader community and with the walleye literature showing that these community shifts tend to reflect a top-down, trophic cascade that stems more from predator–prey relationships than from competitive relationships. Our case study provides important insight into the structure and function of aquatic food webs and the trophic ecology of top predators.

Hatchling Phenotype Of Lake Whitefish Incubated At Increased Temperature During Critical Windows Of Development

Phenotypic plasticity is the ability of an animal to modify its phenotype in response to the environment. Embryos may have critical windows during development when they are particularly plastic or susceptible to the environment. We examined whether there are critical windows during Lake whitefish (Coregonus clupeaformis) embryonic development when temperature has an especially strong effect on phenotype. Lake whitefish are a cold‐water fish species that inhabits the North American Great Lakes. This species lays eggs that develop over winter when lake temperatures are near freezing. With 2°C as the overall control temperature, embryos were incubated at either 5°C, 8°C or 11°C for all of embryonic development or only during one of four distinct windows of development: gastrulation, organogenesis, fin development, and late growth. Survival was monitored throughout development. Hatching characteristics, including time to hatch, mass at hatch, and hatchling oxygen consumption rate, were measured to examine if warmer temperatures during the four windows of development altered hatchling phenotype. No embryos survived to hatch when incubated constantly at 11°C, and survival was reduced at constant 8°C. Survival was also reduced when embryos were incubated at 11°C during the windows of gastrulation, organogenesis and fin development, but not during the late growth window. Time to 50% hatch decreased with an increase in constant incubation temperature, and only during the late growth window did an increase in temperature decrease time to hatch. Increased incubation temperature during the late growth window resulted in smaller hatchlings and reduced yolk conversion efficiency compared to embryos incubated constantly at 2°C or embryos incubated in warmer temperatures during earlier windows of development. Incubation at 11°C during organogenesis, fin development and the late growth window also reduced yolk conversion efficiency. Mass‐specific oxygen consumption rate increased with an increase in constant incubation temperature, but incubation at either 5°C, 8°C or 11°C during gastrulation, organogenesis, fin development or the growth window did not have substantial effects on metabolism at hatch. Overall, critical windows for survival in response to increased temperature were present during gastrulation, organogenesis and fin development. However, hatchling size was most influenced by incubation at warm temperatures during the late growth window prior to hatch, due to increased temperature inducing early hatching.Support or Funding InformationC.A.M. and J.E. were supported by a MITACS Accelerate grant to D.R.B. and J.Y.W. Funding was provided by Bruce Power® and a Collaborative Research and Development Grant from the Natural Sciences and Engineering Research Council of Canada to J.Y.W., R.G.M., and C.M.S.

Daily, Incremental Changes in Incubation Temperature Alter Metabolism and Hatchling Phenotype of Developing Lake Whitefish

Temperature has pervasive effects on poikilotherm physiology, and embryos and newly hatched/born animals are especially vulnerable to temperature shifts. Lake whitefish (Coregonus clupeaformis) are a North American, freshwater lake species with lengthy (80–150 day, 2–8 °C) overwintering embryonic development. Stenothermic, cold‐water embryos may be particularly susceptible to thermal shifts caused by anthropogenic thermal effluent and climate change. We incubated whitefish embryos in petri dishes (N=2000, 6–10 replicates each treatment) at constant treatments of 2.0±0.1°C, 5.0±0.1°C, and 8.0±0.1°C (mean±SD), and in a variable temperature treatment (VT; N=500, each treatment). In the VT, a daily 2°C temperature change (2°C–4°C‐6°C–8°C and back from 8°C‐6°C‐4°C‐2°C) occurred throughout embryonic incubation (mean 5.0±0.3°C). Mortality was quantified as number of hatchlings÷starting embryo number, time to hatch (days post fertilization, dpf) was recorded, and hatchling yolk‐free dry mass was measured. Oxygen consumption rate (VO2 ; N=8–10, each treatment) was measured at 60% of embryonic development and in hatchlings within 3 days post hatching. VO2 was measured for the four treatments (2°C, 5°C, 8°C, VT) at each constant temperature of 2°C, 5°C, and 8°C to determine if V.O2 of VT embryos resembled the VO2 of other treatments. VO2 was measured at 2°C, 5°C, and 8°C after exposing embryos/hatchlings from each treatment to a daily 2°C temperature change, if necessary, until embryos/hatchlings reached the measurement temperature; embryos/hatchlings remained at the measurement temperature for a 24 hr acclimation period, and VO2 was measured. Mortality was significantly affected by treatment (KWRS, P<0.001, Steel‐Dwass post hoc), with 8°C (14.8%±17.6) and VT hatchlings (83.2%±0.07) having a significantly reduced mortality compared to 2°C (88.4%±0.02) and 5°C (90.5%±0.04) hatchlings. Time to hatch (dpf) was significantly different across all treatments (1‐way ANOVA, P<0.001, Duncan post hoc) ‐ 8°C (68±2), VT (111±4), 5°C (116±4), 2°C (170±3). Likewise, hatchling yolk‐free dry mass (mg) was significantly different across all treatments (1‐way ANOVA, P<0.001, Duncan post hoc) ‐ 8°C (0.66±0.08), VT (0.97±0.06), 5°C (1.07±0.03), 2°C (1.36±0.04). VO2 was significantly affected by the interaction between treatment and measurement temperature (2, 5, 8 °C) at 60% of embryonic development and for hatchlings (2‐way ANOVA, P<0.01), and hatchling VT whitefish had a significantly different VO2 compared to 5°C measured at 2, 5 or 8 °C (1‐way ANOVA, P<0.001, Duncan post hoc). This study demonstrates that variable thermal embryonic incubation produces fewer (increased mortality), smaller embryos that hatch earlier. The plasticity of VO2 for this stenothermic‐incubating fish species under variable incubation conditions could represent a metabolic cost to fluctuating thermal incubation conditions.Support or Funding InformationJ.E. and C.A.M. were supported by a MITACS Accelerate grant to D.R.B and J.Y.W. Funding was provided by Bruce Power, Inc. and a Collaborative Research and Development Grant from the Natural Sciences and Engineering Research Council of Canada to J.Y.W., R.G.M., and C.M.S.

Potential health risks posed by polycyclic aromatic hydrocarbons in muscle tissues of fishes from the Athabasca and Slave Rivers, Canada.

Polycyclic aromatic hydrocarbons (PAHs) are released to the environment from oil sands operations and from natural sources in Alberta, Canada. Concentrations of 16 USEPA priority PAHs were measured in tissues of fishes collected from three locations on the Athabasca River in Alberta and two downstream locations on the Slave River in the Northwest Territories, Canada. A total of 425 individual fish were collected including 89 goldeye (Hiodon alosoides), 93 whitefish (Coregonus clupeaformis), 104 northern pike/jackfish (Esox lucius), 96 walleye (Sander vitreus) and 43 burbot/loche mariah/mariah (Lota lota). Fish were sampled during the summer and fall of 2011 and spring of 2012. Dorsal muscle of fishes from upstream reaches of the Athabasca River, close to oil sands extraction and upgrading activities, contained greater concentrations of individual PAHs than concentrations in muscle of fishes from further downstream in the Slave River. Concentrations of the sum of USEPA indicator PAHs (∑PAHs) in fishes collected in the vicinity of Fort McKay, closest to oil sands activities, varied among seasons with average concentrations ranging from 11 (burbot, summer) to 1.2×102ng/g, wm (burbot, spring) with a mean of 48ng/g, wm. Concentrations of ∑PAHs in fishes collected in the vicinity of Fort Resolution, the location most distant from oil sands activities, also varied among species and seasons, with average concentrations ranging from 4.3 (whitefish, summer) to 33ng/g, wm (goldeye, summer) with a mean of 13ng/g, wm. Significant differences in concentrations of ∑PAHs in muscle were observed within goldeye, jackfish, walleye and whitefish among sites. Health risks posed by PAHs to humans were assessed probabilistically using a B[a]P equivalents approach (B[a]Peq). The average lifetime risk of additional cancers for humans who consumed fish was deemed to be within an 'acceptable' range of risk (i.e., less than 10-6).

Mercury Accumulation, and the Mercury-PCB-Sex Interaction, in Lake Whitefish (Coregonus clupeaformis)

We determined whole-fish Hg concentrations of 26 female and 34 male adult lake whitefish (Coregonus clupeaformis) from northern Lake Huron captured during November 2010. Subsampling from these 60 fish, Hg concentration was also determined in both somatic tissue and ovaries (n = 5), while methylmercury (MeHg) concentration was determined in whole fish (n = 18). Bioenergetics modeling was used to assess the growth dilution effect on the difference in Hg concentrations between the sexes. Mean whole-fish Hg concentration in females (59.9 ng/g) was not significantly different from mean whole-fish Hg concentration in males (54.4 ng/g). MeHg accounted for 91% of the mercury found in the lake whitefish. Bioenergetics modeling results indicated that the growth dilution effect did not contribute to the difference in Hg concentrations between the sexes. We estimated that females increased in Hg concentration by 17.9%, on average, immediately after spawning due to release of eggs. Using polychlorinated biphenyl (PCB) data for the same 60 lake whitefish from a previous study, we detected a significant interaction between sex and contaminant type (Hg or PCBs), which was attributable to males being significantly higher in PCB concentration than females. Males may be eliminating Hg at a faster rate than females.

Mixed stock analysis of Lake Michigan's Lake Whitefish Coregonus clupeaformis commercial fishery

Abstract Lake whitefish ( Coregonus clupeaformis ) support the primary commercial fishery in Lake Michigan. Discrete genetic stocks of lake whitefish have been identified and tagging data suggest stocks are mixed throughout much of the year. Our objectives were to determine if (1) differential stock harvest occurs in the commercial catch, (2) spatial differences in genetic composition of harvested fish were present, and (3) seasonal differences were present in the harvest by commercial fisheries that operate in management zones WI-2 and WFM-01 (Green Bay, Lake Michigan). Mixed stock analysis was conducted on 17 commercial harvest samples (n = 78–145/sample) collected from various ports lake-wide during 2009–2010. Results showed significant mixing with variability in stock composition across most samples. Samples consisted of two to four genetic stocks each accounting for ≥ 10% the catch. In 10 of 17 samples, the stock contributing the largest proportion made up

Real-time PCR identification of lake whitefish Coregonus clupeaformis in the Laurentian Great Lakes.

The purpose of this study was to develop a real-time PCR assay to specifically identify lake whitefish Coregonus clupeaformis in larval fish assemblages based on a 122 bp amplicon from the mitochondrial genome. The efficiency of the reaction, as calculated from the standard curve, was 90.77% with the standard curve having an r(2) value of 0.998. Specificity of the assay provided single melt peak in a melt-curve analysis and amplification of only the target species. The assay successfully identified target DNA in as low as 0.1% proportion of a DNA mixture. This assay was designed on the portable Smart Cycler II platform and can be used in both field and laboratory settings to successfully identify C. clupeaformis.

The effects of increased constant incubation temperature and cumulative acute heat shock exposures on morphology and survival of Lake Whitefish (Coregonus clupeaformis) embryos

Increasing incubation temperatures, caused by global climate change or thermal effluent from industrial processes, may influence embryonic development of fish. This study investigates the cumulative effects of increased incubation temperature and repeated heat shocks on developing Lake Whitefish (Coregonus clupeaformis) embryos. We studied the effects of three constant incubation temperatures (2°C, 5°C or 8°C water) and weekly, 1-h heat shocks (+3°C) on hatching time, survival and morphology of embryos, as these endpoints may be particularly susceptible to temperature changes. The constant temperatures represent the predicted magnitude of elevated water temperatures from climate change and industrial thermal plumes. Time to the pre-hatch stage decreased as constant incubation temperature increased (148d at 2°C, 92d at 5°C, 50d at 8°C), but weekly heat shocks did not affect time to hatch. Mean survival rates and embryo morphometrics were compared at specific developmental time-points (blastopore, eyed, fin flutter and pre-hatch) across all treatments. Constant incubation temperatures or +3°C heat-shock exposures did not significantly alter cumulative survival percentage (~50% cumulative survival to pre-hatch stage). Constant warm incubation temperatures did result in differences in morphology in pre-hatch stage embryos. 8°C and 5°C embryos were significantly smaller and had larger yolks than 2°C embryos, but heat-shocked embryos did not differ from their respective constant temperature treatment groups. Elevated incubation temperatures may adversely alter Lake Whitefish embryo size at hatch, but weekly 1-h heat shocks did not affect size or survival at hatch. These results suggest that intermittent bouts of warm water effluent (e.g., variable industrial emissions) are less likely to negatively affect Lake Whitefish embryonic development than warmer constant incubation temperatures that may occur due to climate change.

Temporal stability of lake whitefish genetic stocks in Lake Michigan

Abstract Lake whitefish Coregonus clupeaformis are the predominant species in the Lake Michigan commercial fishing industry. Six genetic stocks were identified in Lake Michigan in 2007; however, genetic structure can fluctuate throughout time due to demographic variables and changing environments. Temporally stable genetic units have a higher probability of containing genetically adaptive traits and thus, are integral components of a sustainable stock-based management approach. The objective of this research was to determine if the genetic stock structure of lake whitefish in Lake Michigan has remained temporally stable from the 1970s through early 2007. Archived scale samples collected by state and tribal agencies during annual assessments from the 1970s, 1980s, and 1990s were used as a source of deoxyribonucleic acid (DNA). Samples were genotyped at 11 microsatellite loci consistent with the contemporary genetic stock dataset. Tests of F ST , Jost's D EST , and Nei's genetic distance were used to compare nine historical sample populations to contemporary stocks. Most stocks showed temporal stability for a majority of the three different analysis methods. The only historical samples to not support the trend of temporal stability were located in the Green Bay region, where two genetic stocks are present in close proximity and are known to have relatively high levels of gene flow between the two stocks. The prevalence of temporal stability gives support to the theory that a stock-based management plan is appropriate for lake whitefish in Lake Michigan.

Fine-Scale Ecological and Genetic Population Structure of Two Whitefish (Coregoninae) Species in the Vicinity of Industrial Thermal Emissions.

Thermal pollution from industrial processes can have negative impacts on the spawning and development of cold-water fish. Point sources of thermal effluent may need to be managed to avoid affecting discrete populations. Correspondingly, we examined fine-scale ecological and genetic population structure of two whitefish species (Coregonus clupeaformis and Prosopium cylindraceum) on Lake Huron, Canada, in the immediate vicinity of thermal effluent from nuclear power generation. Niche metrics using δ13C and δ15N stable isotopes showed high levels of overlap (48.6 to 94.5%) in resource use by adult fish captured in areas affected by thermal effluent compared to nearby reference locations. Isotopic niche size, a metric of resource use diversity, was 1.3- to 2.8-fold higher than reference values in some thermally affected areas, indicative of fish mixing. Microsatellite analyses of genetic population structure (Fst, STRUCTURE and DAPC) indicated that fish captured at all locations in the vicinity of the power plant were part of a larger population extending beyond the study area. In concert, ecological and genetic markers do not support the presence of an evolutionarily significant unit in the vicinity of the power plant. Thus, future research should focus on the potential impacts of thermal emissions on development and recruitment.