Primary and secondary defences of squid to cruising and ambush fish predators : variable tactics and their survival value

Abstract

Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Animal Behaviour 81 (2011): 585-594, doi:10.1016/j.anbehav.2010.12.002.Longfin squid (Loligo pealeii) were exposed to two predators, bluefish (Pomatomus saltatrix) and summer flounder (Paralichthys dentatus), representing cruising and ambush foraging tactics, respectively. During 35 trials, 86 predator–prey interactions were evaluated between bluefish and squid, and in 29 trials, 92 interactions were assessed between flounder and squid. With bluefish, squid predominantly used stay tactics (68.6%, 59/86) as initial responses. The most common stay response was to drop to the bottom, while showing a disruptive body pattern, and remain motionless. In 37.0% (34/92) of interactions with flounder, squid did not detect predators camouflaging on the bottom and showed no reaction prior to being attacked. Squid that did react, used flee tactics more often as initial responses (43.5%, 40/92), including flight with or without inking. When all defence behaviours were considered concurrently, flight was identified as the strongest predictor of squid survival during interactions with each predator. Squid that used flight at any time during an attack sequence had high probabilities of survival with bluefish (65%, 20/31) and flounder (51%, 18/35). The most important deimatic/protean behaviour used by squid was inking. Inking caused bluefish to startle (deimatic) and abandon attacks (probability of survival = 61%, 11/18) and caused flounder to misdirect (protean) attacks towards ink plumes rather than towards squid (probability of survival = 56%, 14/25). These are the first published laboratory experiments to evaluate the survival value of antipredator behaviours in a cephalopod. Results demonstrate that squid vary their defence tactics in response to different predators and that the effectiveness of antipredator behaviours is contingent upon the behavioural characteristics of the predator encountered.This study was funded by the Woods Hole Oceanographic Institution Sea Grant Program, the Massachusetts Marine Fisheries Institute, the University of Massachusetts and the Five College Coastal and Marine Sciences Program. R. T. Hanlon acknowledges partial support from ONR grant N000140610202 and the Sholley Foundation