The role of intraspecific variation in physiological traits in determining vulnerability to capture in fish

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

Field testing a novel high residence positioning system for monitoring the fine‐scale movements of aquatic organisms

1. Acoustic telemetry is an important tool for studying the behaviour of aquatic organisms in the wild. 2. VEMCO high residence (HR) tags and receivers are a recent introduction in the field of acoustic telemetry and can be paired with existing algorithms (e.g. VEMCO positioning system [VPS]) to obtain high‐resolution two‐dimensional positioning data. 3. Here, we present results of the first documented field test of a VPS composed of HR receivers (hereafter, HR‐VPS). We performed a series of stationary and moving trials with HR tags (mean HR transmission period = 1.5 s) to evaluate the precision, accuracy and temporal capabilities of this positioning technology. In addition, we present a sample of data obtained for five European perch Perca fluviatilis implanted with HR tags (mean HR transmission period = 4 s) to illustrate how this technology can estimate the fine‐scale behaviour of aquatic animals. 4. Accuracy and precision estimates (median [5th–95th percentile]) of HR‐VPS positions for all stationary trials were 5.6 m (4.2–10.8 m) and 0.1 m (0.02–0.07 m), respectively, and depended on the location of tags within the receiver array. In moving tests, tracks generated by HR‐VPS closely mimicked those produced by a handheld GPS held over the tag, but these differed in location by an average of ≈9 m. 5. We found that estimates of animal speed and distance travelled for perch declined when positional data for acoustically tagged perch were thinned to mimic longer transmission periods. These data also revealed a trade‐off between capturing real nonlinear animal movements and the inclusion of positioning error. 6. Our results suggested that HR‐VPS can provide more representative estimates of movement metrics and offer an advancement for studying fine‐scale movements of aquatic organisms, but high‐precision survey techniques may be needed to test these systems

Does thermal plasticity affect susceptibility to capture in fish? Insights from a simulated trap and trawl fishery

In fishes, physiological and behavioural traits can correlate with vulnerability to capture with fishing gears, highlighting the capacity of fisheries selection to drive phenotypic change in exploited populations. There remains a paucity of information regarding how different fishing gears may select on phenotypic traits and how relationships between individual traits and capture vulnerability change across environmental gradients. By simulating the capture process in a trawl and trap using wild minnows acclimated to different temperatures, we investigated how contrasting fishing gears select on behavioural and physiological traits, and how this selection is modulated by temperature. Despite similar risk of capture in each gear, selection differed between traps and trawls. Fish exhibiting low spontaneous activity were at greater capture risk in the trawl across all temperatures, while traps showed no selection except at 24°C. No relationships between physiological traits and capture vulnerability were found, except between swim performance and trap capture vulnerability at 24°C. This study demonstrates that fisheries selection on individual traits is likely context-specific, depending on both fishing gear type, and environment

A physiological perspective on fisheries-induced evolution

There is increasing evidence that intense fishing pressure is not only depleting fish stocks but also causing evolutionary changes to fish populations. In particular, body size and fecundity in wild fish populations may be altered in response to the high and often size-selective mortality exerted by fisheries. While these effects can have serious consequences for the viability of fish populations, there are also a range of traits not directly related to body size which could also affect susceptibility to capture by fishing gears – and therefore fisheries-induced evolution (FIE) – but which have to date been ignored. For example, overlooked within the context of FIE is the likelihood that variation in physiological traits could make some individuals within species more vulnerable to capture. Specifically, traits related to energy balance (e.g. metabolic rate), swimming performance (e.g. aerobic scope), neuroendocrinology (e.g. stress responsiveness), and sensory physiology (e.g., visual acuity) are especially likely to influence vulnerability to capture through a variety of mechanisms. Selection on these traits could produce major shifts in the physiological traits within populations in response to fishing pressure that are yet to be considered but which could influence population resource requirements, resilience, species’ distributions, and responses to environmental change

Spatial updating of targets in front and behind

This research compared the accuracy of spatial updating of targets in front with that of targets behind. The participant viewed a target on the ground several meters away and then, without vision, sidestepped along a guide rope while trying to mentally update the location of the target. On some trials, the target location was in front as the person sidestepped and, on other trials, the target location was behind. Participants responded by facing the updated target location with eyes closed. The results indicate that people are able to update target locations behind them very nearly as well as target locations in front

A role for lakes in revealing the nature of animal movement using high dimensional telemetry systems

Movement ecology is increasingly relying on experimental approaches and hypothesis testing to reveal how, when, where, why, and which animals move. Movement of megafauna is inherently interesting but many of the fundamental questions of movement ecology can be efficiently tested in study systems with high degrees of control. Lakes can be seen as microcosms for studying ecological processes and the use of high-resolution positioning systems to triangulate exact coordinates of fish, along with sensors that relay information about depth, temperature, acceleration, predation, and more, can be used to answer some of movement ecology's most pressing questions. We describe how key questions in animal movement have been approached and how experiments can be designed to gather information about movement processes to answer questions about the physiological, genetic, and environmental drivers of movement using lakes. We submit that whole lake telemetry studies have a key role to play not only in movement ecology but more broadly in biology as key scientific arenas for knowledge advancement. New hardware for tracking aquatic animals and statistical tools for understanding the processes underlying detection data will continue to advance the potential for revealing the paradigms that govern movement and biological phenomena not just within lakes but in other realms spanning lands and oceans.Correction published here, October 2021: https://doi.org/10.1186/s40462-021-00285-3</p

A role for lakes in revealing the nature of animal movement using high dimensional telemetry systems

Movement ecology is increasingly relying on experimental approaches and hypothesis testing to reveal how, when, where, why, and which animals move. Movement of megafauna is inherently interesting but many of the fundamental questions of movement ecology can be efficiently tested in study systems with high degrees of control. Lakes can be seen as microcosms for studying ecological processes and the use of high-resolution positioning systems to triangulate exact coordinates of fish, along with sensors that relay information about depth, temperature, acceleration, predation, and more, can be used to answer some of movement ecology’s most pressing questions. We describe how key questions in animal movement have been approached and how experiments can be designed to gather information about movement processes to answer questions about the physiological, genetic, and environmental drivers of movement using lakes. We submit that whole lake telemetry studies have a key role to play not only in movement ecology but more broadly in biology as key scientific arenas for knowledge advancement. New hardware for tracking aquatic animals and statistical tools for understanding the processes underlying detection data will continue to advance the potential for revealing the paradigms that govern movement and biological phenomena not just within lakes but in other realms spanning lands and oceans. Telemetry, Sensor, Biologging, Movement ecology, Fish ecolog