Food color and marine turtle feeding behavior: Can blue bait reduce turtle bycatch in commercial fisheries?

We conducted laboratory and field experiments to investigate the behavioral responses of Kemp's ridley Lepidochelys kempii and loggerhead turtles Caretta caretta to whole squid dyed different colors. Our ultimate goal was to identify bait modifications that could reduce the interaction of turtles with longline fishing gear. In captivity, both turtle species clearly preferred untreated squid over squid that had been dyed dark blue. Loggerhead turtles also preferred untreated squid over red-dyed squid, whereas Kemp's ridley showed the opposite response. Field trials of blue-dyed bait were conducted on commercial fishing boats in the Gulf of Papagayo, Costa Rica, where the incidental capture of olive ridley turtles Lepidochelys olivacea is high (long-term average, approximately 7 turtles per 1000 hooks). We found no differences in rates of turtle interactions (8.4 and 8.1 individuals per 1000 hooks) when using untreated versus blue-dyed baits. Although effective in laboratory settings with captive turtles, dyeing bait does not appear to have potential as an effective mitigation measure to reduce sea turtle bycatch in longline fisheries.