Physiological and behavioural consequences of capture and retention in carp sacks on common carp (Cyprinus carpio L.), with implications for catch-and-release recreational fishing

Common carp (Cyprinus carpio L.) captured by specialised carp anglers are often retained in so-called “carp sacks” and released after substantial retention periods of several hours duration. Little is known about the lethal and sub-lethal (e.g., physiological disturbances, behavioural impairments) consequences associated with this practice. In this study, the effects of capture and retention in carp sacks on the physiological status of small hatchery-reared carp were examined at two moderate water temperatures (12 °C and 22 °C) in a laboratory setting, where water quality changes in carp sacks were also studied. A complementary field approach was used to examine the effects of carp sack retention on physiology, tissue damage, short-term behaviour and long-term fate of large feral carp in Dow’s Lake, a lentic section of the Rideau Canal in Ottawa, Ontario, Canada. During retention for up to 9 h, decreasing plasma lactate levels suggested recovery from initial capture stress, yet there was evidence of pronounced primary and secondary physiological stress responses resulting from the combined capture and retention in carp sacks in both the laboratory and the field. In addition, there was evidence of tissue damage in carp retained in carp sacks for long periods. The moderate water temperatures studied did not strongly affect the stress response in carp, and changes in water quality parameters within carp sacks were minor and likely not of biological relevance. Physiological changes were associated with impaired post-release behaviour reflecting a tertiary stress response, but recovery was rapid within a couple of hours post-release. No mortalities occurred in a two month observation period. Our findings indicate that despite being sublethally affected by capture and retention, carp are able to recover rapidly with negligible mortality from retention in carp sacks like those used in the present study.