Reproductive resilience: a paradigm shift in understanding spawner‐recruit systems in exploited marine fish

Abstract

A close relationship between adult abundance and stock productivity may not exist for many marine fish stocks, resulting in concern that the management goal of maximum sustainable yield is either inefficient or risky. Although reproductive success is tightly coupled with adult abundance and fecundity in many terrestrial animals, in exploited marine fish where and when fish spawn and consequent dispersal dynamics may have a greater impact. Here, we propose an eco‐evolutionary perspective, reproductive resilience, to understand connectivity and productivity in marine fish. Reproductive resilience is the capacity of a population to maintain the reproductive success needed to result in long‐term population stability despite disturbances. A stock's reproductive resilience is driven by the underlying traits in its spawner‐recruit system, selected for over evolutionary timescales, and the ecological context within which it is operating. Spawner‐recruit systems are species specific, have both density‐dependent and fitness feedback loops and are made up of fixed, behavioural and ecologically variable traits. They operate over multiple temporal, spatial and biological scales, with trait diversity affecting reproductive resilience at both the population and individual (i.e. portfolio) scales. Models of spawner‐recruit systems fall within three categories: (i) two‐dimensional models (i.e. spawner and recruit); (ii) process‐based biophysical dispersal models which integrate physical and environmental processes into understanding recruitment; and (iii) complex spatially explicit integrated life cycle models. We review these models and their underlying assumptions about reproductive success vs. our emerging mechanistic understanding. We conclude with practical guidelines for integrating reproductive resilience into assessments of population connectivity and stock productivity.

Shifts in North Sea forage fish productivity and potential fisheries yield

“…However, other studies point to changes in zooplankton species composition as the cause of reduced fish growth (Beaugrand et al, 2003;Van Deurs, Jørgensen, & Fiksen, 2015). Factors such as spawning site diversity or the frequency of unlikely events governing extreme recruitment outburst (Lowerre-Barbieri et al, 2016;Pepin, 2015) have also been proposed as drivers of variation in fish stock production. However, such mechanisms would not be expected to influence growth as found in the present study.…”

Ecological and Evolutionary Consequences of Environmental Change and Management Actions for Migrating Fish

“…Earlier work unanimously show that among-individual variation contributes to improved establishment, more stable populations, and reduced extinction risk of populations and species, via complementarity and/or variance reducing effects (Hughes et al, 2008;Simberloff, 2009;Forsman, 2014;Forsman and Wennersten, 2016;Des Roches et al, 2018). Lastly, portfolio effects associated with variation among populations across environments or with high species diversity may increase stability, productivity and resilience of species and ecosystems (Schindler et al, 2010(Schindler et al, , 2015Waldman et al, 2016;Hui et al, 2017;Lowerre-Barbieri et al, 2017).…”

“…Apart from immediate negative effects associated with declining populations, changes in distribution ranges, and local extinctions (Dudgeon et al, 2006), exploitation can induce long-term evolutionary shifts in behaviors, individual growth trajectories and life-history strategies. These in turn may affect the recruitment, size-structure and dynamics of populations (Beacham, 1983;Kuparinen and Merilä, 2007;Uusi-Heikkila et al, 2008;Lowerre-Barbieri et al, 2017).…”

“…This is essential both because it can stabilize productivity of individual species (Schindler et al, 2010), and because there can be a critical threshold for the number of populations below which regional extinction is likely (Hui et al, 2017). Maintaining options and portfolios for organism and their ecosystems is a means of spreading the risk and maintaining productivity, biodiversity and ecosystem functioning in the face of future uncertainties (Schindler et al, 2015;Waldman et al, 2016;Lowerre-Barbieri et al, 2017).…”

Oogenesis and reproductive investment of Atlantic herring are functions of not only present but long-ago environmental influences as well

“…The predictive power of useful relationships typically diminishes over time when the blend of influential abiotic and biotic drivers change (4,5). Due to the high importance of getting a grip on the expected level of recruitment (REC) for quota decisions, one practical solution is to assume the same REC as in preceding years.…”