Focusing on what matters most: Evaluating multiple challenges to stability in recreational fisheries

Recreational fisheries were traditionally theorized to self-regulate in a sustainable feedback loop in which recreational anglers moderate their fishing effort in response to population declines. However, several mechanisms are hypothesized to break down this self-regulatory process, including recruitment variability and depensatory population dynamics. Although many of these mechanisms of instability have been estimated in empirical systems and explored using modelling, we still do not know the extent to which these mechanisms can (1) erode stability at their observed strength in real systems and (2) interact to dampen or intensify each other's effects. In this study, we synthesize existing data on four of these mechanisms: (1) depensation in the stock-recruit relationship, (2) recruitment stochasticity, (3) density-dependent catchability and (4) the strength of anglers' responsiveness to changing catch rates. We report the range of observed values for these four mechanisms in real-world fisheries and observe their effect on a simplified recreational fishery model. We find that at moderate fishing effort none of the mechanisms was destabilizing enough on its own to collapse the modelled population, but that an angler population that was likely to keep fishing when catch rates approached zero was a key element of interactions that caused collapse. The strongest interaction was between an angler population with this characteristic and a fish population with hyperstable catch rates. Our results highlight the need for more consistent and widespread estimation of utility-based angler effort functions as well as the importance of interdisciplinary teams that can gather both social and ecological data.