Fishing‐induced changes in adult length are mediated by skipped‐spawning

Abstract

Elucidating fishing effects on fish population dynamics is a critical step toward sustainable fisheries management. Despite previous studies that have suggested age or size truncation in exploited fish populations, other aspects of fishing effects on population demography, e.g., via altering life histories and density, have received less attention. Here, we investigated the fishing effects altering adult demography via shifting reproductive trade-offs in the iconic, overexploited, Pacific bluefin tuna Thunnus orientalis. We found that, contrary to our expectation, mean lengths of catch increased over time in longline fisheries. On the other hand, mean catch lengths for purse seine fisheries did not show such increasing trends. We hypothesized that the size-dependent energetic cost of the spawning migration and elevated fishing mortality on the spawning grounds potentially drive size-dependent skipped spawning for adult tuna, mediating the observed changes in the catch lengths. Using eco-genetic individual-based modeling, we demonstrated that fishing-induced evolution of skipped spawning and size truncation interacted to shape the observed temporal changes in mean catch lengths for tuna. Skipped spawning of the small adults led to increased mean catch lengths for the longline fisheries, while truncation of small adults by the purse seines could offset such a pattern. Our results highlight the eco-evolutionary dynamics of fishing effects on population demography and caution against using demographic traits as a basis for fisheries management of the Pacific bluefin tuna as well as other migratory species.

Importance of interindividual interactions in eco‐evolutionary population dynamics: The rise of demo‐genetic agent‐based models

“…For example, selective fishing (or harvesting) directly affects competition among surviving fish (or trees), while genetic composition determines optimal fishing (or harvesting) patterns. In particular, different DG‐ABMs were used to understand how selective fishing can affect the demography and evolution of fish populations (fisheries‐induced evolution), through cascading and sometimes counterintuitive effects on population demographic structure, growth and maturation thresholds (Ayllón et al, 2018 ; Piou et al, 2015 ; Wang et al, 2017 ; Wang & Höök, 2009 ). By simultaneously modelling the plastic and genetic responses of individuals, DG‐ABMs can also disentangle the role of selective fishing and environment in the observed and predicted population declines and phenotypic changes (Piou et al, 2015 ).…”

Realizing the potential of trait‐based approaches to advance fisheries science

“…Jacobsen, Essington, & Thorson, ; Laslett, Eveson, & Polacheck, ; Pilling, Kirkwood, & Walker, ; Sinclair, Swain, & Hanson, ; Wang & Ellis, ) and reproduction (Rowe, Hutchings, Skjæraasen, & Bezanson, ; Scott & Heikkonen, ). This is particularly true as it relates to the increasing interest in the influence of environment, habitat (Hutchings et al, ; Morrongiello & Thresher, ) and fishing (Lowerre‐Barbieri, Ganias, Saborido‐Rey, Murua, & Hunter, ; Wang, Chen, Hsu, & Shen, ) on the relative success of alternative life‐history strategies among individuals within a population (Conover, Arnott, Walsh, & Munch, ).…”