Incorporating estuarine-angler behaviour and delayed blood sampling into the rapid assessment of catch-and release angling on the iconic dusky kob Argyrosomus japonicus

Argyrosomus japonicus is arguably South Africa's most important estuarine recreational and small-scale fishery species. Although juvenile A. japonicus predominate in estuarine environments, where catch-and-release angling is common, limited C & R studies have taken place. The aim of this study was to use angler-behaviour to robustly examine the physiological stress response, reflex impairment and short-term (12-36-hour) survival of A. japonicus following C & R angling. Observations of estuarine recreational angling informed three air exposure treatments based on minimum (10 s), mean (75 s) and maximum (240 s) observed times, for use in a controlled angling experiment. Based on a prior laboratory study, blood sampling was delayed 30-40 min post-capture to allow for peak accumulations of lactate and glucose. Long air exposure (240 s) predicted significantly higher blood glucose concentrations (ANOVA, p = 0.03) than short (10 s) exposure. Similarly, both long (p = 0.01) and moderate (75 s; p = 0.01) air exposure significantly predicted elevated blood lactate concentrations, when compared with short exposure. In terms of physical impairment, long air exposure (240 s) had a significant negative influence on the reflex response (cumulative link model, p = 0.01) of A. japonicus. An observed short-term mortality of 7.7% was primarily attributed to hooking injury. To reduce significant physiological and physical stress, it is proposed that anglers should aim to reduce air exposure times to below the observed mean of 75 s, and ideally to 10 s. For relevant and meaningful future C & R studies, we propound the incorporation of angler behavioural assessments, and the investigation of physiological stress responses, prior to designing field studies.

Automated summary

This study investigated the physiological stress response and short-term survival of Argyrosomus japonicus following catch and release angling by using angler-behavior examination. The results showed that longer air exposure time led to higher blood glucose and lactate concentrations and negatively affected the reflex response of A. japonicus. It is suggested that anglers should reduce air exposure time to below 75 seconds, ideally to 10 seconds, to minimize physiological and physical stress on A. japonicus.