Theory suggests that wild animals will try to maximize their net energy gains per unit time foraging, as precious energy must also be spent elsewhere, like reproduction, guarding offspring, mates or territory. Thus, foraging must be efficient. Foraging tactics can be influenced by prey type and availability, habitat, seasonality, unique individual preferences, genetic predispositions and can be diverse even among closely related species. The toothed whales, Odontocetes, are one such group where tactics can vary. Some killer whales (Orcinus orca) tear large prey apart, some swallow fish whole head first, while others have others have very specialized handling techniques.
Dolphins around the world have been observed employing different strategies. Wild rough-toothed dolphins (Steno bredanensis) have been documented striping the flesh off mahi-mahi (Coryphaena hippurus). The Amazon River dolphin (Inia geoffrensis) is unique in that it crushes armored prey (e.g., river turtles, Podocnemis sextuberculata and crabs, Poppiana argentiniana) with modified rear teeth before swallowing whole. Bottlenose dolphins (Tursiops aduncus and Tursiops truncatus) have shown to remove the cuttlebone of cuttlefish (Sepia spp.) prior to consumption in the Indo-Pacific and Portuguese waters respectively.
Work by Ronje et al 2017 in the northern gulf of Mexico also highlights another specialization of T.truncatus the common bottlenosed dolphin. On May 7, 2015, Ronje and his colleagues were surveying dolphins off Mississippi’s Petit Bois Island when they observed a very odd phenomenon: a half-kilometer trail of severed catfish heads floating in the path of a dolphin pod. The quickly collected the decapitated catfish heads. Back in the lab the heads were “cleaned” with flesh-eating beetles to get a better idea of the beheading process. As it turns out the heads of catfish, hardhead catfish and gafftopsail catfish, Bagre marinus, were not haphazardly bitten off, but precisely beheaded. The catfishes best defense is their skull structure which cradles rigid dorsal and pectoral spines that angle away from the body, which coincidentally are also poisonous. Thus, if swallowed complicating the swallowing process and potentially causing dangerous wounds.
However, not all dolphins in the region are so clever, as records of stranded dolphins show 38 records of those which suffered injuries from catfish spines. One body in fact had 17 catfish spines, some of which had punctured the digestive tract. This implies that not all dolphins forage upon catfish in this specialized beheading behavior. Photos from three severed-head sites in the gulf recognized the same eight dolphins. Therefore, could it be akin to a family? Is this a learned behavior? Cultural transmission?
Please see the full PLoS article:
Ronje EI, Barry KP, Sinclair C, Grace MA, Barros N, Allen J, et al. (2017) A common bottlenose dolphin (Tursiops truncatus) prey handling technique for marine catfish (Ariidae) in the northern Gulf of Mexico. PLoS ONE 12(7): e0181179. https://doi.org/10.1371/journal.pone.0181179
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0181179
