Condition and post‐release mortality of angled Northern Pike temporarily retained on stringers

Abstract

Anglers typically use stringers to keep fish intended for harvest from spoiling or for high grading purposes (i.e., culling). However, relatively few studies have examined the effects of temporary stringer retention on the physical condition and post‐release mortality of fish. In this study, we examined blood physiology, reflex impairment, injury and 48‐hour fate of 168 Northern Pike Esox lucius after being exposed for 2 hours on one of five treatments: 1) cord stringer through the operculum, 2) cord stringer through the lower jaw, 3) metal stringer through the operculum, 4) metal stringer through the lower jaw, and 5) aerated tank control. Immediately after retention, blood lactate concentrations of stringer treatments were on average 42% greater relative to controls. Fish from the stringer treatments exhibited injuries of varying severity, most of which (e.g., gill lesions, expanded puncture wounds, swelling), were still present on surviving fish 48 hours later.. Reflexes were impaired for all stringer fish whereas control fish tended to have all reflexes intact. No fish died during the treatment period. The highest occurrence of mortality was within the first 8 hours following retention for the cord‐operculum (48%), metal‐jaw (15%), and metal‐operculum (19%) treatments. Stringers placed through the operculum had a higher mortality rate (37%) compared to stringers placed through the lower jaw (17%), regardless of stringer type. Overall, 27% of fish placed on stringers died and 68% of the remaining fish showed injuries related to stringers, while control fish showed low mortality (7%) and no meaningful injuries. Our results suggest that holding fish on stringers causes stress and injury levels that can result in post‐release mortality. As such, fisheries managers should consider restricting the release of fish placed on stringers, and once placed on a stringer, fish should be regarded as part of the daily harvest‐limit for a given angler.