Using logbook data to determine the immediate mortality of blue sharks (Prionace glauca) and tiger sharks (Galeocerdo cuvier) caught in the commercial U.S. pelagic longline fishery

Citation
Dapp DR, Huveneers C, Walker TI, et al (2016) Using logbook data to determine the immediate mortality of blue sharks (Prionace glauca) and tiger sharks (Galeocerdo cuvier) caught in the commercial U.S. pelagic longline fishery. FB 115:27–41. doi: 10.7755/FB.115.1.3
Abstract

Identifying effective methods of reducing shark bycatch in hook-based fisheries has received little attention despite reports of declines in some shark populations. Previously proposed shark bycatch mitigation measures include gear modifications, time and area closures, avoidance of areas with high shark abundance, use of repellents, and use of specific bait types. Regardless of the method of shark bycatch reduction, knowledge of the effects of the chosen method on the catch rates of targeted fish species should be understood. To examine the effects of bait type on catch rates of sharks and teleosts on bottom longline gear, standardized gear was deployed with bait alternating between Atlantic mackerel (Scomber scombrus) and northern shortfin squid (Illex illecebrosus). For all shark species examined, except the scalloped hammerhead (Sphyrna lewini), a preference for hooks baited with Atlantic mackerel was observed. Commercially and recreationally important teleosts had no significant preference for a specific bait, with the exception of the red drum (Sciaenops ocellatus), which had a significant preference for hooks baited with northern shortfin squid. Bait preference decreased as total catch rate increased on individual longline sets. Our results point to the use of specific baits as a viable method to reduce shark catch rates without decreasing catches of targeted teleosts.