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

Authored by Hui-Yu Wang, Ying-Shiuan Chen, Chien-Chung Hsu, Sheng-Feng Shen

Date Published: 2017

DOI: 10.1002/eap.1441

Sponsors: Ministry of Science and Technology of Taiwan

Platforms: No platforms listed

Model Documentation: Other Narrative

Model Code URLs: Model code not found

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.

Tags

fisheries Cod gadus-morhua North pacific Life-history evolution Biphasic growth Pacific bluefin tuna Induced disruptive selection Dependent energy allocation Age-structure Thunnus-orientalis Fishing-induced evolution Adult demography Eco-genetic individual-based modeling Fisheries selectivity Life history trade-offs Pacific bluefin tuna Thunnus orientalis