George E. Morgan

Inbreeding, outbreeding and environmental effects on genetic diversity in 46 walleye (Sander vitreus) populations

Genetic diversity is recognized as an important population attribute for both conservation and evolutionary purposes; however, the functional relationships between the environment, genetic diversity, and fitness‐related traits are poorly understood. We examined relationships between selected lake parameters and population genetic diversity measures in 46 walleye (Sander vitreus) populations across the province of Ontario, Canada, and then tested for relationships between six life history traits (in three categories: growth, reproductive investment, and mortality) that are closely related to fitness, and genetic diversity measures (heterozygosity, d2, and Wrights inbreeding coefficient). Positive relationships were observed between lake surface area, growing degree days, number of species, and hatchery supplementation versus genetic diversity. Walleye early growth rate was the only life history trait significantly correlated with population heterozygosity in both males and females. The relationship between FIS and male early growth rate was negative and significant (P < 0.01) and marginally nonsignificant for females (P = 0.06), consistent with inbreeding depression effects. Only one significant relationship was observed for d2: female early growth rate (P < 0.05). Stepwise regression models showed that surface area and heterozygosity had a significant effect on female early growth rate, while hatchery supplementation, surface area and heterozygosity had a significant effect on male early growth rate. The strong relationship between lake parameters, such as surface area, and hatchery supplementation, versus genetic diversity suggests inbreeding and outbreeding in some of the populations; however, the weak relationships between genetic diversity and life history traits indicate that inbreeding and outbreeding depression are not yet seriously impacting Ontario walleye populations.

Growth and food of young-of-the-year brook charr,Salvelinus fontinalis, in lake and creek environments

SynopsisGrowth and diet of brook charr,Salvelinus fontinalis, during their first weeks of exogenous feeding were compared between the nearshore zone of a central Ontario lake and its small, inlet creeks. Food selection was related to size and age of charr and possibly availability of food items. Mean growth was similar between habitats despite differences in consumed food types and caloric values. Differences in social behaviour may have been responsible for different patterns of growth between habitats. The importance of creek habitats to the dynamics and fitness of lake populations of brook charr are suggested.

Prey life-history and bioenergetic responses across a predation gradient.

To evaluate the importance of non-consumptive effects of predators on prey life histories under natural conditions, an index of predator abundance was developed for naturally occurring populations of a common prey fish, the yellow perch Perca flavescens, and compared to life-history variables and rates of prey energy acquisition and allocation as estimated from mass balance models. The predation index was positively related to maximum size and size at maturity in both male and female P. flavescens, but not with life span or reproductive investment. The predation index was positively related to size-adjusted specific growth rates and growth efficiencies but negatively related to model estimates of size-adjusted specific consumption and activity rates in both vulnerable (small) and invulnerable (large) size classes of P. flavescens. These observations suggest a trade-off between growth and activity rates, mediated by reduced activity in response to increasing predator densities. Lower growth rates and growth efficiencies in populations with fewer predators, despite increased consumption suggests either 1) a reduction in prey resources at lower predator densities or 2) an intrinsic cost of rapid prey growth that makes it unfavourable unless offset by a perceived threat of predation. This study provides evidence of trade-offs between growth and activity rates induced by predation risk in natural prey fish populations and illustrates how behavioural modification induced through predation can shape the life histories of prey fish species.

The Role of Ciscoes as Prey in the Trophy Growth Potential of Walleyes

Abstract Analysis of the growth characteristics of 215 populations of walleye Sander vitreus across Ontario revealed that female walleyes reached larger asymptotic lengths in lakes in which ciscoes Coregonus artedi provided a relatively large prey species for them. The stomach contents of walleyes from a set of intensively studied lakes revealed that walleyes of all sizes depended on ciscoes but that ciscoes were most important to larger walleyes. In lakes without ciscoes, the walleye diet closely tracked the availability of young-of-year yellow perch Perca flavescens; when such prey were in short supply, walleyes consumed invertebrates. The prey size in walleye stomachs was significantly larger in lakes with ciscoes, but the probability of finding empty stomachs was also greater. This suggests that although walleyes in lakes with ciscoes foraged less often, more energy was available for growth. Exceptions to this general pattern occurred when ciscoes were too large to be consumed by walleyes or ciscoes w...

Effects of Recreational Fishing on the Population Dynamics of Lake-Dwelling Brook Trout

Abstract Data collected over 7 consecutive years were used to examine the population dynamics of the exploited brook trout Salvelinus fontinalis of Meach Lake in central Ontario. Numbers of age-1 and older trout averaged 975 among years. The largest trout were 490 mm long and weighed 1,807 g. Few trout lived beyond age 4. Annual mortality rates varied among age-classes and between sexes; average total instantaneous mortality was 0.95 and average total and fishing mortalities were 78% and 44%, respectively. Exploitation was greatest for age-2 and age-3 brook trout of both sexes. Catchability was uncorrelated with abundance. There was evidence of density-dependent growth at age-2 or age-3 but no indication of density-dependent mortality. A “hockey stick” model appeared to best describe the stock–recruitment relationship. Abundance of potential competitors was not correlated with brook trout size, although abundance of white suckers Catostomus commersoni was correlated with numbers of age-2 male brook trout....

Historical and Anthropogenic Factors Affecting the Population Genetic Structure of Ontario’s Inland Lake Populations of Walleye (Sander vitreus)

Populations existing in formerly glaciated areas often display composite historical and contemporary patterns of genetic structure. For Canadian freshwater fishes, population genetic structure is largely reflective of dispersal from glacial refugia and isolation within drainage basins across a range of scales. Enhancement of sport fisheries via hatchery stocking programs and other means has the potential to alter signatures of natural evolutionary processes. Using 11 microsatellite loci genotyped from 2182 individuals, we analyzed the genetic structure of 46 inland lake walleye (Sander vitreus) populations spanning five major drainage basins within the province of Ontario, Canada. Population genetic analyses coupled with genotype assignment allowed us to: 1) characterize broad- and fine-scale genetic structure among Ontario walleye populations; and 2) determine if the observed population divergence is primarily due to natural or historical processes, or recent anthropogenic events. The partitioning of genetic variation revealed higher genetic divergence among lakes than among drainage basins or proposed ancestries-indicative of relatively high isolation among lakes, study-wide. Walleye genotypes were clustered into three major groups, likely reflective of Missourian, Mississippian, and Atlantic glacial refugial ancestry. Despite detectable genetic signatures indicative of anthropogenic influences, province-wide spatial genetic structure remains consistent with the hypothesis of dispersal from distinct glacial refugia and subsequent isolation of lakes within primary drainage basins. Our results provide a novel example of minimal impacts from fishery enhancement to the broad-scale genetic structure of inland fish populations.

Examining policy preferences of recreationists: A case of a fisheries management plan

Abstract We showcase a stated preference choice modelling approach that is ideally suited to provide information about recreationists’ preferences for different recreational management plans. In particular, we employ a stated preference choice model to examine anglers’ preferences for walleye management plans in eastern Ontario, Canada. This choice model approach with its emphasis on trade‐offs allows us to assess whether support for walleye regulations is affected by the expected catch and size of walleye that would likely be produced by the regulations. We also examine differences in angling preferences for regulations through a latent‐class model that is jointly estimated with the choice model. The results suggest that anglers do make trade‐offs among regulations and expected outcomes and that anglers do have different preferences for regulations and expected outcomes.

Biomass of benthic invertebrates unaffected by industrial damage to lakes despite effects on species composition

Historic metal mining and smelting in the area of Sudbury, Ontario, has resulted in lakes with elevated levels of metals in the sediment, low inputs of terrestrial organic material, and unusual fish communities which led to severe changes in the benthic invertebrate community. Using broad-scale surveys of lakes from Sudbury and an undisturbed reference area, we used multivariate methods to tease apart potential influences of predation by fish, habitat availability, and toxicity of the environment on the biomass of benthic invertebrates. In contrast to many other studies, our response variable is benthic invertebrate biomass—a more relevant factor in food web processes than the numeric densities that are more typically studied. Despite differences in species composition, we observed very similar total benthic invertebrate biomass in Sudbury lakes and reference lakes. Redundancy analysis revealed that different factors shaped invertebrate biomass in the two study areas. Sudbury benthos was strongly influenced by the fish community and metal toxicity with only slight effects of habitat quality. Overall, the fact that benthic invertebrate biomass was similar to reference systems suggests that Sudbury communities may be able to function normally despite the strong direct and indirect effects of multiple stressors.