The Physiological Effects of Angling on Post-Release Survivorship in Tunas, Sharks, and Marlin
G. B. Skomal and B. C. Chase
Large numbers of tunas, sharks, and marlin are released annually by recreational and commercial rod-and-reel fishermen off the east coast of the United States. This is largely due to the federal imposition of quotas, minimum sizes, and bag limits on offshore anglers, coupled with a growing conservation ethic. Catch data collected in Massachusetts from 1991 to 1998 indicate that, on average, 96% of the blue sharks Prionace glauca, 75% of the school bluefin tuna Thunnus thynnus, 30% of the yellowfin tuna Thunnus albacares, and 99% of the white marlin Tetrapturus albidus were released annually by big game tournament participants. However, the extent to which angling affects post-release survivorship is unknown in these species. Increased angler-induced mortality will have important implications in release and quota management strategies.
Tunas, sharks, and billfish possess large amounts of anaerobic white muscle that reflects an ability of high work output in short bursts. Angling practices result in increased anaerobic activity, muscular fatigue, and time out of water. The physiological consequences of angling stress are poorly understood in large pelagic fishes. Available evidence supports the notion that high anaerobic muscular activity in fish causes extreme homeostatic disruptions that may impede normal physiological and behavioral function and, ultimately, reduce survivorship (Wood et al. 1983; Wood 1991; Milligan 1996). Since blood reflects changes in muscle biochemistry, these perturbations can be measured and quantified (Wells et al. 1986).