Capture-induced physiological stress and postrelease mortality for southern bluefin tuna (Thunnus maccoyii) from a recreational fishery

Southern bluefin tuna (SBT; Thunnus maccoyii) are a popular component of the recreational large pelagic game fishery in Australia. The fishery is managed using individual fisher catch limits. Fifty-nine pop-up archival transmitting (PAT) tags were attached to individual SBT to estimate postrelease survival (PRS) rates. Fish caught on lures configured with J-hooks (n = 44) and those caught on circle hooks (n = 8) had similar PRS rates and were combined to increase sample size, revealing a PRS estimate of 83.0% (95% CI: 75.9%–90.7%, n = 54). The PRS estimate of fish caught on lures with treble hooks was much lower, 60% (95% CI: 20%–100%, n = 5). By sampling blood from 233 fish, including 56 of the PAT-tagged individuals, we show that angling duration is related to an elevation of lactate, cortisol, and osmolarity in blood plasma, indicative of increased physiological stress. Physical damage related to hooking location, angling duration, biochemical indicators of physiological stress, and handling duration were not identified as significant factors leading to postrelease mortality. The results quantify a previously unaccounted source of mortality for SBT.