Summary Assessment and monitoring of exploited fish populations are challenged by costs, logistics and negative impacts on target populations. These factors therefore limit large‐scale effective management strategies. Evidence is growing that the quantity of eDNA may be related not only to species presence/absence, but also to species abundance. In this study, the concentrations of environmental DNA (eDNA) from a highly prized sport fish species, Lake Trout Salvelinus namaycush (Walbaum 1792), were estimated in water samples from 12 natural lakes and compared to abundance and biomass data obtained from standardized gillnet catches as performed routinely for fisheries management purposes. To reduce environmental variability among lakes, all lakes were sampled in spring, between ice melt and water stratification. The eDNA concentration did not vary significantly with water temperature, dissolved oxygen, pH and turbidity, but was significantly positively correlated with relative fish abundance estimated as catch per unit effort (CPUE), whereas the relationship with biomass per unit effort (BPUE) was less pronounced. The value of eDNA to inform about local aquatic species distribution was further supported by the similarity between the spatial heterogeneity of eDNA distribution and spatial variation in CPUE measured by the gillnet method. Synthesis and applications. Large‐scale empirical evidence of the relationship between the eDNA concentration and species abundance allows for the assessment of the potential to integrate eDNA within fisheries management plans. As such, the eDNA quantitative method represents a promising population abundance assessment tool that could significantly reduce the costs associated with sampling and increase the power of detection, the spatial coverage and the frequency of sampling, without any negative impacts on fish populations.

Variations in larval fish growth rates are largely the result of variability in biotic and abiotic characteristics of the feeding environment experienced by each individual. An assessment of an individual's overall feeding success (i.e. accumulation of utilizable organic matter) can best be achieved at the time of capture when the relationships among environment, short-term feeding success as defined by gut content and long-term feeding success as defined by accumulated growth can be contrasted. Here, we investigated the relationships between average growth, feeding success, and variability in individual growth and feeding rates across a range of taxa based on a synthesis of studies in which stomach content and otolith growth were measured in the same individuals. Instantaneous measures of feeding success were highly variable and demonstrated a positive yet somewhat limited association with growth rates across all taxa. The strength of the feeding-growth relationships among taxa, and cohorts within taxa, was reflected in the autocorrelation of individual growth rates, suggesting that stable growth was achieved through consistent feeding success. However, when viewed at the individual level, faster growth was achieved in individuals with more variable growth rates, and by inference more variable past feeding success. The dichotomy in these underlying relationships may point to the importance of stochastic events in the development of exceptional individuals in a population, and may be linked to how surplus energy is allocated to individual growth rates. The positive correlation found between feeding success and growth in all taxa is consistent with the growth-survival paradigm for the larval stage of fish. However, both the correlation between feeding success and growth and the serial correlation of growth time-series was greatest in fast-growing species, suggesting that the potential for an early “critical period” regulating survival varies among species, reaching a maximum in fast-growing fish.

The principal objective of this study was to test the hypothesis that enhanced early growth of yellow perch Perca flavescens in lakes affected by forest harvesting was related to favorable feeding conditions after the perturbation. Yellow perch larvae and juveniles and their zooplankton prey were sampled three times in three unperturbed lakes and in three perturbed lakes where forest harvesting had occurred in the catchment 2 years earlier. Univariate and multivariate analyses of the diets of age‐0 yellow perch from both treatments showed that fish in perturbed lakes primarily preyed upon Daphnia spp. and Polyphemus pediculus, whereas fish in unperturbed lakes preyed upon more diverse food items. Perturbed lakes showed higher dissolved organic carbon concentrations, algal biomass, and Daphnia spp. abundance. The feeding success index (number of prey items in the stomach per millimeter of fish length) and recent growth rates of age‐0 yellow perch showed a significant type II functional relationship with the abundance of Daphnia spp. We hypothesized that the increase in Daphnia spp. abundance and a darkening of water color in perturbed lakes may have favored prey detection and growth for larval and juvenile yellow perch, thereby affecting population recruitment.

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