How ecological processes shape the outcomes of stock enhancement and harvest regulations in recreational fisheries

Abstract

Fish stocking and harvest regulations are frequently used to maintain or enhance freshwater recreational fisheries and contribute to fish conservation. However, their relative effectiveness has rarely been systematically evaluated using quantitative models that account for key size- and density-dependent ecological processes and adaptive responses of anglers. We present an integrated model of freshwater recreational fisheries where the population dynamics of two model species affect the effort dynamics of recreational anglers. With this model, we examined how stocking various fish densities and sizes (fry, fingerlings, and adults) performed relative to minimum-length limits using a variety of biological, social, and economic performance measures, while evaluating trade-offs. Four key findings are highlighted. First, stocking often augmented the exploited fish population, but size- and density-dependent bottlenecks limited the number of fry and fingerlings surviving to a catchable size in self-sustaining populations. The greatest enhancement of the catchable fish population occurred when large fish that escaped early bottlenecks were stocked, but this came at the cost of wild-stock replacement, thereby demonstrating a fundamental trade-off between fisheries benefits and conservation. Second, the relative performance of stocking naturally reproducing populations was largely independent of habitat quality and was generally low. Third, stocking was only economically advisable when natural reproduction was impaired or absent, stocking rates were low, and enough anglers benefitted from stocking to offset the associated costs. Fourth, in self-sustaining fish populations, minimum-length limits generally outperformed stocking when judged against a range of biological, social and economic objectives. By contrast, stocking in culture-based fisheries often generated substantial benefits. Collectively, our study demonstrates that size- and density-dependent processes, and broadly the degree of natural recruitment, drive the biological, social, and economic outcomes of popular management actions in recreational fisheries. To evaluate these outcomes and the resulting trade-offs, integrated fisheries-management models that explicitly consider the feedbacks among ecological and social processes are needed.

A future without stocking? The importance of harvest and river regulation for long-term population viability of migratory salmonids

“…Adopting such an approach for the Hunder trout would be beneficial for quantifying past and future impact of stocking on genetic variation. It could also aid in developing strategies for enhancing stocking practices to minimise negative genetic and demographic impacts (Araki & Schmid 2010) and for weighing different stocking practices against compensatory mitigation measures (Johnston et al 2018, Arlinghaus et al 2002, Janowitz-Koch et al 2018.…”

“…Populations reduced to critically low numbers have been saved from the brink of extinction by supplementation (Tallmon et al 2004, Hostetler et al 2013, and long-term stocking programmes may be able to ensure the persistence of heavily exploited populations even if they have lost their capacity to reproduce naturally (e.g. through loss of recruitment habitat, Rogers et al 2010, Ziegler et al 2017, Johnston et al 2018.…”

Impact of recreational fisheries management on fish biodiversity in gravel pit lakes with contrasts to unmanaged lakes

“…The effect of stocking on the presence of species is likely strongest in the early introductory phase when abundant ecological niches are available for colonization. Recent research, however, has shown that once a species is naturally recruiting, stocking with juveniles has no effect on biomass and stock size, e.g., in Esox lucius (Johnston et al in press; Hü hn et al , 2014). This means that once the initial establishment phase is over, continued angler stocking should particularly affect non-naturally recruiting predatory fishes (Johnston et al in press), in our case Anguilla anguilla .…”

Frontiers in modelling social–ecological dynamics of recreational fisheries: A review and synthesis

“…These questions are potentially complex, due for instance to variation in the objectives of stocking programs (e.g. population rehabilitation vs. put-take or put-grow-take) or in the interactions of stocking with habitat suitability (Johnston et al, 2018). Several other fishery system processes are likely avenues for future advances.…”