Eric A. Parkinson

Canada's Recreational Fisheries: The Invisible Collapse?

Abstract Fishing for recreation is a popular activity in many parts of the world and this activity has led to the development of a sector of substantial social and economic value worldwide. The maintenance of this sector depends on the ability of aquatic ecosystems to provide fishery harvest. We are currently witnessing the collapse of many commercial marine fisheries due to over-exploitation. Recreational fisheries are typically viewed as different from commercial fisheries in that they are self-sustaining and not controlled by the social and economic forces of the open market that have driven many commercial fisheries to collapse. Here we reject the view that recreational and commercial fisheries are inherently different and demonstrate several mechanisms that can lead to the collapse of recreational fisheries. Data from four high profile Canadian recreational fisheries show dramatic declines over the last several decades yet these declines have gone largely unnoticed by fishery scientists, managers, an...

ENERGY ALLOCATION STRATEGY IN YOUNG FISH: ALLOMETRY AND SURVIVAL

We observed substantial variation in seasonal growth rates, autumn body size, and growing-season mortality among eight experimental cohorts of age-O rainbow trout, Oncorhynchus mykiss. Wet mass, water, lipids (storage), and lipid-free dry mass (structure) had biphasic allometries with inflexions at - 10 cm in length. Dry:wet mass and storage:structure ratios were positively related to fish length, indicating that the relative quantities of these constituents change with body size. Lipid concentration varied according to a sigmoid relationship with wet mass which also had a growth-rate dependence. Inde- pendent assessments of the allometry of growing-season survival and winter metabolism facilitated assessment of the costs and benefits of two alternate energy allocation strategies of young fish. For cohorts with low growth rates and small autumn body size, a somatic growth rate maximization strategy is optimum, producing a 5% net survival advantage over an energy storage maximization strategy. For cohorts with intermediate growth rates and autumn mass, somatic growth and energy storage strategies lead to similar first-year sur- vival. The fastest growing cohorts are estimated to have a net survival advantage of 7%, by adopting an energy storage maximization strategy over a growth rate maximization strategy.

Predators select against high growth rates and risk-taking behaviour in domestic trout populations

Domesticated (farm) salmonid fishes display an increased willingness to accept risk while foraging, and achieve high growth rates not observed in nature. Theory predicts that elevated growth rates in domestic salmonids will result in greater risk–taking to access abundant food, but low survival in the presence of predators. In replicated whole–lake experiments, we observed that domestic trout (selected for high growth rates) took greater risks while foraging and grew faster than a wild strain. However, survival consequences for greater growth rates depended upon the predation environment. Domestic trout experienced greater survival when risk was low, but lower survival when risk was high. This suggests that animals with high intrinsic growth rates are selected against in populations with abundant predators, explaining the absence of such phenotypes in nature. This is, to our knowledge, the first large–scale field experiment to directly test this theory and simultaneously quantify the initial invasibility of domestic salmonid strains that escape into the wild from aquaculture operations, and the ecological conditions affecting their survival.

DENSITY‐DEPENDENT PROCESSES IN STRUCTURED FISH POPULATIONS: INTERACTION STRENGTHS IN WHOLE‐LAKE EXPERIMENTS

The goal of this study is to identify the mechanisms and measure the strengths of interactions within and among size classes in experimental populations of rainbow trout, Onchoranchus mivkiss. The metric that we used to assess the density-dependent effects was based on consumptive allometry and predator-prey theory. We demonstrate that the inter- actions among size classes were asymmetrical, favoring larger-bodied individuals. Descrip- tions of diet and spatial resource use, measures of prey availability, and risk to intra-specific interactions allowed assessment of the relative contributions of exploitative and interference competitive interactions among size classes. Growth of the larger classes was strongly density-dependent and driven primarily by exploitative competition. Growth of the smallest size class was controlled by a combination of exploitative competition within and among size classes and interference competition with larger-bodied conspecifics. This combination of interactions among size classes within populations resulted in a body-size-based asymmetry favoring the larger size classes. Sur- vival of all size classes was positively related to both body size and growth rate. We speculate that the net result of these processes within size-structured populations is compensatory, leading to stable population dynamics.

FROM INDIVIDUALS TO POPULATIONS: PREY FISH RISK-TAKING MEDIATES MORTALITY IN WHOLE-SYSTEM EXPERIMENTS

Recent research suggests that the behavior of individuals under risk of pre- dation could be a key link between individual behavior and population and community dynamics. Yet existing theory remains largely untested at large spatial and temporal scales. We manipulated food available to age-0 rainbow trout while at risk of cannibalism, in a replicated factorial whole-lake experiment, to test whether the trade-off between growth and mortality rates is mediated by foraging activity by young fish under predation risk. We found that this trade-off exists for young fish at the whole-system scale, and that food- dependent behavioral variation has large mortality consequences. In high-food lakes, age- 0 trout spent less time moving, fewer individuals swam continuously, and those swimming continuously swam at slower speeds relative to those in low-food lakes. Age-0 trout also used deep, risky habitats less when food was abundant. This lower activity, combined with avoidance of risky habitats, coincided with 68% higher survival in high-food lakes. If general, this trade-off may be a key mechanism linking individual behavior to population- level processes in size-structured populations.

Mitochondrial DNA variation in rainbow trout ( Oncorhynchus mykiss ) across its native range: testing biogeographical hypotheses and their relevance to conservation

North‐western North America has been repeatedly glaciated over most of the past two million years, with the most recent glaciation occurring between 60 000 and 10 000 years ago. Intraspecific genetic variation in many species has been shaped by where they survived glaciation and what postglacial recolonization routes were used. In this study, molecular techniques were used to investigate biogeographical, taxonomic and conservation issues in rainbow trout, Oncorhynchus mykiss. Mitochondrial DNA (mtDNA) variation was assessed using a restriction fragment length polymorphism (RFLP) analysis, focusing mainly on the previously understudied northern extent of the species’ range. Two phylogenetically distinct mitochondrial lineages were found that differed from each other by up to 1.8% in sequence. Although the geographical distributions of the two clades overlap extensively, diversity and distributional analyses strongly suggest that trout survived glaciation in both coastal and inland refugia followed by postglacial gene flow and secondary contact. Postglacial dispersal into British Columbia most likely occurred from the Queen Charlotte Islands and the Columbia River. Although trout most likely also survived glaciation along the coast of Washington, Oregon and California, as well as near the Bering Strait, evidence suggests that dispersal into British Columbia from these areas was limited. Sequence analysis of mitochondrial haplotypes revealed higher diversity in California than in the northern part of the species’ range, indicating an ancient presence of the species in the south. Phylogeographic divergence probably predates adaptive variation in the species as suggested by evidence for parallel evolution of life history types across the range of O. mykiss.

Linking Angling Catch Rates and Fish Learning under Catch-and-Release Regulations

Abstract Many recreational fisheries are subject to varying degrees of catch-and-release fishing through regulations and conservation-minded anglers. Clearly, releasing a proportion of the catch improves conservation of the fishery, yet it is not clear how the released catch contributes to angling quality. If fish change their behavior to lower their individual catchability after they have been caught, then angler catch rates may not be proportional to fish density. Therefore, even catch-and-release fisheries could exhibit poor angling quality if there is sufficiently high angler effort. We tested this idea by experimentally fishing five small lakes that contained rainbow trout Oncorhynchus mykiss in the interior of British Columbia. We found that with sustained effort of 8 angler-hours · d−1 · ha−1 and complete release of the catch, catch rates quickly dropped within 7–10 d. Given the individual capture histories of tagged fish, the most parsimonious catchability model incorporated learning and heterogen...

The origins of ecotypic variation of rainbow trout: a test of environmental vs. genetically based differences in morphology

Although morphological plasticity has been observed in a variety of taxa, few experimental studies have compared the relative proportion of morphological variability that is accounted for by environmentally induced plasticity, and how much is because of genetically based differences among populations. We compared the morphology of six rainbow trout (Oncorhynchus mykiss) populations from different ecotypic categories that were raised under flowing vs. standing‐water conditions. Our data indicate that both environmental conditions and ecotypic differences account for a significant proportion of variation in morphology. Among ecotype effects, however, accounted for a much larger proportion of morphological variability than environmental conditions. Rainbow trout from stream populations had deeper caudal peduncles, and longer fins than lake populations, and rainbow trout from a piscivorous population had larger mouth and head lengths than all other ecotypes. Environmentally induced differences in morphology were primarily related to differences in mouth and head lengths, as well as fin length. Relative to morphometric differences from natural rainbow trout populations, most characteristics deviated in the same direction in our experimental populations. Our data indicate that morphological differences across rainbow trout populations have a genetic basis and may represent locally adaptive characteristics and highlight the role of ecology in promoting phenotypic divergence.

POPULATION CONSEQUENCES OF A PREDATOR-INDUCED HABITAT SHIFT BY TROUT IN WHOLE-LAKE EXPERIMENTS

In a replicated whole-lake experiment, we (a) tested for the existence of a flexible habitat shift in response to predator presence in age-0 rainbow trout (Oncorhynchus mykiss) at risk of cannibalism and (b) evaluated the population-level consequences of habitat shifts in terms of growth and survival over their first growing season. Daphnid food and adult trout predators were substantially more abundant in pelagic than in littoral habitats. Age-0 trout used all habitats in populations without adult trout predators, whereas age-0 trout were observed only in the less profitable littoral habitat in populations with adult trout. Consequently, mean fall mass of age-0 trout in the presence of predators was almost half that observed in populations without adult trout. Despite the shift in habitat use, age- 0 trout experienced 90% mortality when adult trout predators were present, in comparison to only 36% mortality when absent. We conclude that the commonly observed habitat shifts by fish at risk of predation, observed at smaller scales, do in fact occur at the whole-system scale over long time intervals. These results suggest that fish are able to perceive risk at large spatial scales and thus take advantage of profitable (but normally risky) habitats when predators are absent, or move to less profitable refuge habitats when predators are present.

Predictive Models of Fish Species Distribution in the Blackwater Drainage, British Columbia

Abstract Management of fish biodiversity and individual fish species requires the ability to understand and predict expected species distributions. Models predicting species distributions can provide insight into habitat requirements, help identify unique outlier populations, and determine potential biodiversity hotspots. Our goal was to determine whether reliable models of species distributions could be developed for freshwater fish in British Columbia using large-scale macrohabitat data. We surveyed 48 stream sites in a British Columbia drainage with high species diversity (the Blackwater River) and developed statistical models based on macrohabitat variables to describe fish species distributions. Classification rates (i.e., the proportion of sites correctly classified by the model) of our logistic regression models based solely on map-based variables were generally high (73–90%) for most fish species found in the Blackwater River drainage. Including field-measured variables produced significantly bett...