Hook ingestion rates in loggerhead sea turtles Caretta caretta as a function of animal size, hook size, and bait

Declines in sea turtle populations worldwide have been attributed in part to incidental capture in hook and line fisheries. Methods to reduce turtle bycatch and mortality must strike a balance between bycatch reduction and target species retention if they are to gain acceptance from fishers. To investigate potential bycatch reduction measures, we examined the effects of hook size, bait type, baiting technique, and animal size on the frequency of loggerhead sea turtles Caretta caretta ingesting a baited hook during controlled trials. Results indicated that as hook size increased, the likelihood for deep ingestion decreased. Smaller turtles were less likely to swallow larger hooks. Turtles were less likely to swallow hooks baited with sardines than with squid and single-baited rather than threaded baits. Results are likely due to differences in bait texture, hook shielding effects, and turtles' behavioral differences. We suggest that fishing with large hooks, using finfish instead of squid, and using single-baited instead of threaded baits might reduce deep ingestion rates of hooks by loggerheads as large as 65 cm in standard straight carapace length (notch to tip).