Turning performance of brief squid Lolliguncula brevis during attacks on shrimp and fish

Abstract

Although squid are generally considered to be effective predators, little is currently known quantitatively about how squid maneuver and position themselves during prey strikes. In this study, high-speed video and kinematic analyses were used to study attacks by brief squid Lolliguncula brevis on both shrimp and fish. Squid attack success was high (>80%) and three behavioral phases were identified: (1) approach, (2) strike and (3) recoil. Lolliguncula brevis demonstrated greater maneuverability (i.e., a smaller length-specific turning radius) and employed more body adjustments (i.e., mantle angle posturing) during approaches toward shrimp versus fish. Squid exhibited higher linear approach/strike velocities and accelerations with faster swimming fish prey compared to slower shrimp prey. Agility (i.e., turning rate) during prey encounters was comparable to performance extremes observed during non-predatory turns, and did not differ according to prey type or distance. Despite having the ability to modulate tentacle extension velocity, squid instead increased their own swimming velocity rather than increasing tentacle velocity when targeting faster fish prey during the strike phase, but this was not the case for shrimp prey. Irrespective of prey type, L. brevis consistently positioned themselves above the prey target prior to the tentacle strike, possibly to facilitate a more advantageous downward projection of the tentacles. During the recoil, L. brevis demonstrated length-specific turning radii similar to those recorded during the approach despite vigorous escape attempts by some prey. Clearly, turning performance is integral to prey attacks in squid, with differences in attack strategy varying depending on the prey target.