Hypoxia alters vulnerability to capture and the potential for trait-based selection in a scaled-down trawl fishery

Humans can affect the rate and trajectory of the evolution of organisms through selective harvest. Due to non-random targeting of individuals and high rates of mortality, commercial fishing can produce particularly strong selective pressures. Although numerous studies have documented the evolutionary impacts of fishing, little is known about the combined effects of environmental change and fishing-associated selection on physiological and behavioural traits.

Here, using zebrafish(Danio rerio) as a model organism in a scaled-down trawl fishery, we show that capture rate increases by ∼7-fold under hypoxic conditions (35%airsaturation) as compared to fishing in normoxia. Additionally, the repeat ability of both capture vulnerability and swimming performance decreases considerably, suggesting that oxygen availability can affect selection on particular traits.

The increase in capture vulnerability is accompanied by a decrease in swimming performance(as indicated by critical swimming speed) during exposure to hypoxia, suggesting a functional link between these two integrative phenotypic traits. We observed no strong relationship between capture vulnerability and metabolic variables (standard metabolic rate and maximum metabolic rate).Our findings highlight that prevailing environmental conditions can influence harvest-associated selectivity by influencing trait repeatability and altering among individual trait variation.

These effects suggest a disrupted capacity for trait-based selection in an increasingly hypoxic aquatic environment.