Abstract
Modified handling is often claimed to reduce (sub-)lethal impacts among organisms caught-and-released in fisheries. Improving welfare of discarded fish warrants investigation, when their survival is of both economic and ecological importance. In this study, juvenile yellowfin bream (Acanthopagrus australis) were trawled in an Australian penaeid fishery and then discarded after on-board sorting in either dry or water-filled (modified) trays and with delays in starting sorting of either 2 or 15 mins. Blood plasma cortisol, glucose and potassium were sampled immediately from some yellowfin bream, while others were placed into cages (with controls) and sampled after five days. Irrespective of their on-board handling, all trawled fish incurred a relatively high acute stress response (i.e. an increase in Mean ± SE cortisol from a baseline of <4 to 122.0 ± 14.9 ng/mL) that was mostly attributed to the trawling process, and exacerbated by variation in key parameters (low salinity, changes in water temperature and the presence of jellyfish Catostylus mosaicus in catches). When C. mosaicus was present, the potassium concentrations of fish sampled immediately after sorting were significantly elevated, possibly due to nematocyst contact and subsequent inhibition of ion pumps or cytolysis. Stress also increased during handling in response to warmer air temperatures and longer exposure. While most fish had substantially recovered by 120 hours after discarding, deploying selective trawls (to reduce jellyfish) for short periods and then quickly sorting catches in water would benefit discard welfare.
Highlights
The discarding of unwanted organisms during fishing is perceived as ecologically and economically wasteful; if most discards die [1]
One-hundred-and-ninety-two yellowfin bream were sampled for blood
The results from this study indicate that being caught and discarded by penaeid trawls evokes a considerable acute stress response in yellowfin bream with plasma cortisol concentrations among T0 fish comparable to the mean range of peak post-stress levels observed for >10 species after similar capture-related stimuli [33]
Summary
The discarding of unwanted organisms during fishing is perceived as ecologically and economically wasteful; if most discards die [1]. Beyond immediate mortalities are potentially deleterious physiological effects that may impair the fitness of surviving individuals by compromising their health, growth and reproductive output [1,2,3,4,5,6] Some of these impacts may be reduced via more benign on-board handling practices, such as minimising air exposure among teleosts [7, 8]; the benefits of which have been demonstrated for several species after capture by passive gears such as hook-and-line [9]. Rapid increases in plasma catecholamines by chromaffin cells result in elevated plasma cortisol as a primary response, with secondary effects including changes in glucose [19, 20] and hydrominerals such as potassium due to electrolytic disturbances [18, 21] All of these responses may be compounded by prolonged exposure to air, thermal or haline shock [16, 20]. Among some pink snapper (Pagrus auratus), acute capture and handling stress disrupted endocrine reproductive processes, including decreased gonadal steroid concentrations or gamete quality [22]
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