Abstract
An improved understanding of bycatch mortality can be achieved by complementing field studies with laboratory experiments that use physiological assessments. This study examined the effects of water temperature and the duration of net entanglement on physiological disturbance and recovery in coho salmon (Oncorhynchus kisutch) after release from a simulated beach seine capture. Heart rate was monitored using implanted electrocardiogram biologgers that allowed fish to swim freely before and after release. A subset of fish was recovered in respirometers to monitor metabolic recovery, and separate groups of fish were sacrificed at different times to assess blood and white muscle biochemistry. One hour after release, fish had elevated lactate in muscle and blood plasma, depleted tissue energy stores, and altered osmoregulatory status, particularly in warmer (15 vs. 10°C) and longer (15 vs. 2 min) capture treatments. A significant effect of entanglement duration on blood and muscle metabolites remained after 4 h. Oxygen consumption rate recovered to baseline within 7–10 h. However, recovery of heart rate to routine levels was longer and more variable, with most fish taking over 10 h, and 33% of fish failing to recover within 24 h. There were no significant treatment effects on either oxygen consumption or heart rate recovery. Our results indicate that fishers should minimize handling time for bycatch and maximize oxygen supply during crowding, especially when temperatures are elevated. Physiological data, such as those presented here, can be used to understand mechanisms that underlie bycatch impairment and mortality, and thus inform best practices that ensure the welfare and conservation of affected species.
Highlights
Recent studies suggest climate warming is affecting the distribution and phenology of fishes [1,2], yet the relatively inflexible life history of some species means that changes in distribution may be limited and thermal tolerance must keep pace with the warming environment [3]
This study examined the effects of water temperature and the duration of net entanglement on physiological disturbance and recovery in coho salmon (Oncorhynchus kisutch) after release from a simulated beach seine capture
At Cultus Lake Laboratory (CLL), fish were held in the transport tank, within which dissolved oxygen was maintained between 85–120% saturation, and were dip-netted individually for surgery prior to transfer into either of two large, circular concrete ponds (5.3 m diameter)
Summary
Recent studies suggest climate warming is affecting the distribution and phenology of fishes [1,2], yet the relatively inflexible life history of some species means that changes in distribution may be limited and thermal tolerance must keep pace with the warming environment [3]. In Pacific salmon (Oncorhynchus spp.), spawning stream fidelity and fixed reproductive schedules mean that fish have little or no choice about what water temperatures or fisheries they will encounter during upstream spawning migrations. High river temperatures (e.g., 18+ °C; [4]) can presumably act as a selective force because they cause mortality via disrupted physiological homeostasis or acceleration of pathogen development [4,5,6,7,8]. The strategy of releasing certain species or populations for conservation purposes hinges on post-release recovery and high survival rates for fish exposure to what is an acute exercise stressor (capture and handling). The interaction between water temperature and fisheries capture stressors is of increasing relevance to management, as salmon-bearing rivers are projected to continue to warm [3,11,12]
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