The interactive effects of physiology and climate change on capture vulnerability of individual fish

There is increasing evidence that intense commercial fishing pressure is not only depleting fish stocks but also causing evolutionary changes to fish populations. In particular, a wide body of research suggests size-selective harvesting is altering growth rates, body size, and fecundity in wild fish populations. More recent work also suggests that there are a range of traits besides body size which could also affect the vulnerability of fish to fishing gears - and therefore the fisheries-induced evolution. For example, within a given species, variation in physiological traits related to energy demand and swimming ability are especially likely to influence vulnerability to capture through a variety of mechanisms. Critically, many of the same traits that may make individuals vulnerable to capture by fishing could also be linked to a fish's sensitivity to climate change. For fishes, factors such as aerobic capacity, swimming performance, metabolic rate and feeding levels are all affected by ambient temperature. Therefore, as fish are exposed to varying environmental conditions while moving throughout a habitat, the individuals that are most susceptible to capture may change depending on the prevailing temperature. Novel modelling approaches that incorporate behaviour and respiratory constraints are well suited to generate predictions for how populations may respond to the synergistic effects of fishing and climate change. However, such models urgently need information on how physiological phenotypes affect vulnerability of individual fish to capture in a natural setting. We propose to use current technology for tracking the movements of wild fish to examine: (1) whether individual variability in thermal physiology affects habitat use and vulnerability to capture; and (2) if selection on phenotypes by fishing make fish populations less able to cope with changing climates. Indeed, fishing may be causing evolutionary changes to the intrinsic physiological traits of fish that have so far gone unnoticed but which could be crucial for influencing species' geographic distributions, resilience, and capacity to respond to environmental degradation. This multi-disciplinary project will address this critical gap in knowledge by generating data on trait-based capture vulnerability and habitat use in a natural environment and then feeding this data directly into a modelling framework for understanding the interactive effects of fishing and climate change on populations over various timescales.

The most immediate non-academic beneficiaries of this work will be the general public. A major advantage of this project for engaging with the general public is the inherently interest that people have in fisheries and anthropogenic impacts on the environment. Although many people are aware of overfishing as a threat to marine systems, most are not aware of the evolutionary impact that fishing has on the fish that remain. Killen has previously given public talks at the Glasgow Science Festival and British Science Festival on the topic of fisheries induced evolution. In every instance, the talks have been well-received with a high degree of audience participation and interaction. In general the topic of fisheries-induced evolution presents an ideal platform for showcasing the principles of biology, ecology, and evolution, and illustrating the effects of environmental change because it is a topic that people can relate to and want to hear about.

In the longer term, policy makers could also be benefit from the results of the project with specific regard to impacts of commercial fisheries and environmental change. Specific policy changes that are foreseeable include changes to fishing practices (e.g. gear design or deployment strategies) which minimise selection on phenotypes, particularly traits that would erode a population's ability to respond to environmental change. Model forecasts for adaptability to the multiple stressors imposed by overfishing and climate change could also have implications for fisheries management. Evolving fish stocks create a problem for fisheries management and policy because shifting individual traits and population reference points make it difficult to calculate how demands on individuals translate into fisheries-level properties such as stock biomass, food demand, and sustainability. In a broader perspective, it is also unclear whether FIE is degrading the ability to rebound after fishing pressure is alleviated, particularly in the face of environmental change. To date a main factor underlying this uncertainty is a critical lack of knowledge regarding how fish physiology is being affected by FIE. The current project will serve to address this gap in knowledge.