title: The role of intraspecific variation in physiological traits in determining vulnerability to capture in fish
Creators: name: Hollins, Jack P.W.
Publisher: name: University of Glasgow
Year: 2020
Subjects: subject: Physiology, fisheries induced evolution, telemetry, stable isotope analysis, respirometry, ecophysiology.

description: Impacts of fisheries induced evolution (FIE) may extend beyond life history traits to more cryptic aspects of biology, such as behaviour and physiology. Understanding roles of physiological traits in determining individual susceptibility to capture in fishing gears, and how these mechanisms change across contexts is essential to evaluate the capacity of commercial fisheries to elicit phenotypic change in exploited populations. In particular, physiological traits related to metabolism, bioenergetics, and swim performance may affect the probability of fish interacting with a fishing gear, or successfully escaping it once it has been encountered, and so may also be under selection in commercial and recreational fisheries. Selection on these traits has the capacity to alter the physiological composition of exploited fish populations in response to fishing pressure, with consequences for the viability of fish stocks, and the sustainability of fisheries exploitation. Evaluating the capacity of fisheries to elicit phenotypic change in exploited fish stocks is complicated by the myriad different fishing gears used around the world, and their contrasting mechanisms of capture, as well as the modulating effect of environment on relationships between individual traits and capture vulnerability. This thesis made use of both laboratory and field-based experiments, alongside data collected from commercially important species in a real world fisheries context to establish mechanistic links between individual physiological traits and capture vulnerability in different gears, the degree to which these relationships may be modulated by the environment, and how fisheries selection may alter the ecological niche of exploited species. Using laboratory experiments, I investigated the role of environmental context in determining relationships between individual physiological traits and capture vulnerabilities in different gear types. Trawling simulations conducted on groups of Minnows comprised of individuals familiar with one another, and of individuals which had never seen each other before showed that social context can alter relationships between individual traits and capture vulnerability. When swimming among familiar conspecifics, a negative relationship between trawl capture vulnerability and anaerobic metabolic capacity was found, while no relationship between individual traits and capture vulnerability was found when fish faced the trawl alongside unfamiliar shoalmates. In contrast, a subsequent experiment investigating links between physiological traits of minnows and capture vulnerability in replicated trawl and trap trials found no relationship between metabolic traits and capture vulnerability in either gear at any temperature. However, the trawl still selected on fish behaviour with high activity fish at less risk of capture at all temperatures tested. These laboratory experiments are accompanied by two studies of fisheries selection in the wild. The first used a combination of lab based behavioural assays, respirometry and acoustic telemetry to investigate the capacity for two different fishing methods (gill netting and angling) to select on the physiological and behavioural traits of perch. This study found that gillnetted perch showed broader patterns of habitat use than their angled conspecifics, suggesting that gill nets selected on the spatial traits of wild fish. No differences in physiological traits between gear types was found. Finally, a similar comparative approach was used to investigate the capacity for trawling and jigging to select on contrasting ecological traits of wild cod. Jigging was found to selectively remove fish with low δ15N values, most likely through a mechanism of feeding motivation, while the trawl was found to be less selective on ecological traits. These results highlight the capacity for fishing gears to select on cryptic aspects of fish biology, such as patterns of space use, feeding motivation, and swim performance, but also show that these relationships can be strongly dependent on the external environment.