Chew, shake, and tear: Prey processing in Australian sea lions (Neophoca cinerea)

Abstract

Pinnipeds generally target relatively small prey that can be swallowed whole, yet often include larger prey in their diet. To eat large prey, they must first process it into pieces small enough to swallow. In this study we explored the range of prey‐processing behaviors used by Australian sea lions (Neophoca cinerea) when presented with large prey during captive feeding trials. The most common methods were chewing using the teeth, shaking prey at the surface, and tearing prey held between the teeth and forelimbs. Although pinnipeds do not masticate their food, we found that sea lions used chewing to create weak points in large prey to aid further processing and to prepare secured pieces of prey for swallowing. Shake feeding matches the processing behaviors observed in fur seals, but use of forelimbs for “hold and tear” feeding has not been previously reported for other otariids. When performing this processing method, prey was torn by being stretched between the teeth and forelimbs, where it was secured by being squeezed between the palms of their flippers. These results show that Australian sea lions use a broad repertoire of behaviors for prey processing, which matches the wide range of prey species in their diet.

Hawaiian monk seals exhibit behavioral flexibility when targeting prey of different size and shape

“…One seal was occasionally observed making repeated dorso-ventral motions of the lower jaw and gular region when using suction feeding to consume night smelt (5.88% of night smelt suction feeding trials) after prey was inside the mouth prior to swallowing. This behavior has been observed in other pinnipeds and is sometimes referred to as chewing (Hocking et al, 2014(Hocking et al, , 2015(Hocking et al, , 2016Kienle et al, 2018).…”

“…The largest prey (herring) was ∼80% of the Hawaiian monk seal's head length, and seals used more pierce feeding on herring compared with the smaller prey types. If we had presented Hawaiian monk seals with even larger prey (>80% of the seal's head length), we predict that the seals would have switched to using more biting than suction feeding, which has been observed in other pinnipeds (Hocking et al, 2014(Hocking et al, , 2015(Hocking et al, , 2016. Hawaiian monk seals also showed behavioral flexibility in their feeding kinematics.…”

“…Many marine animals exhibit behavioral flexibility when feeding to overcome spatial and temporal heterogeneity in prey resources (Dill, 1983;Schoen et al, 2018;McHuron et al, 2018). For example, many species of pinnipeds (seals, sea lions and walruses) change their foraging behavior in response to abiotic and biotic conditions, including prey (Bowen et al, 2002;Hocking et al, 2015Hocking et al, , 2016, feeding context (Marshall et al, 2008(Marshall et al, , 2014(Marshall et al, , 2015Hocking et al, 2014), habitat (Páez-Rosas et al, 2014), season (Breed et al, 2009;Cotté et al, 2015) and oceanographic conditions (Simmons et al, 2010;Villegas-Amtmann et al, 2017;Abrahms et al, 2017), resulting in increased foraging success. However, other pinnipeds show little flexibility when feeding and appear constrained to a particular feeding strategy (e.g.…”

Pop-up satellite archival tags reveal evidence of intense predation on large immature Chinook salmon (Oncorhynchus tshawytscha) in the North Pacific Ocean

“…If these events are attributed to predation, based on feeding strategies and gape limitations, the most probable predator is either a species of pinniped or a resident killer whale. Pinnipeds are known to tear apart prey before consuming them (Hocking et al 2016(Hocking et al , 2017, while killer whales are known to roll after capture of prey and also to carry and share salmon prey, during which time they are torn to pieces (Ford and Ellis 2006). However, the overall high frequency of predation events attributed to salmon sharks may suggest that unknown mortality was at least partially caused by individuals of this species, which either did not consume the entire tagged fish or immediately expelled the PSAT subsequent to predation.…”

A behavioural framework for the evolution of feeding in predatory aquatic mammals

“…Notable exceptions are otters, which have a well-developed complex dentition; otariid pinnipeds, which use chewing to generate weak points in prey that make it more likely to tear during further processing [37,38]; and, possibly, the Amazon river dolphin, which is the only extant cetacean bearing weakly heterodont teeth [39]. Besides chewing, prey can be processed by tearing it between teeth and forelimbs [38]. Alternatively, a prey item can be dismembered using the jaws only, either by actively grabbing it with the teeth and shaking it (e.g.…”