Mortality rate of striped marlin (Tetrapturus audax) caught with recreational tackle

A project was initiated in the autumn of 2000 to document the mortality of striped marlin caught on recreational fishing tackle, with a follow-up study conducted in autumn of 2001. Fish were caught using typical recreational fishing methods and 80 pop-up satellite archival tags were deployed with new software and mechanical release mechanisms that allowed tags to detach and transmit early if the fish died. The first year study was also designed to compare the effectiveness and associated mortality of circle hooks versus J-hooks, while the second year study compared offset and non-offset circle hooks. All fish were caught on live bait. Circle hooks were found to be equally effective in hooking and landing striped marlin and far less likely to cause serious bleeding or become lodged in areas other than the mouth. Non-offset and 5degrees offset circle hooks had very similar performance. Depth and temperature records allowed us to determine the fate of individual marlin following release. In total, 16 of 61 fish died (mortality rate of 26.2%), all within 5 days of release (mean 1.5 days). Injury was a clear predictor of mortality; 100% of fish that were bleeding from the gill cavity died, 63% of fish hooked deep died, and 9% of those released in good condition died.