'Burial at sea' : consumption and dispersal of large fish and cetacean food-falls by deep-sea scavengers in the abyssal Northeast Atlantic Ocean and Eastern Mediterranean Sea
The fate of cetacean carcasses in the deep-sea was investigated using autonomous lander vehicles incorporating time-lapse camera and acoustic tracking systems, as well as fish and amphipod traps. Four lander deployments placed cetacean carcasses at depths of 4000-4800m in the Northeast Atlantic for periods of 36h, 152h, 276h and 480h, before being recovered. The photographic sequences revealed that the soft tissue of carcasses was consumed at rates varying from 0.05-0.48kg.h-1, depending on how intact the carcass was. In each deployment, approximately 1h after emplacement, the grenadier Coryphaenoides (Nematonurus) armatus and large numbers of lysianassid amphipods had arrived at the food-fall. Amphipods appeared to be the only scavengers able to feed directly on the carcass. They tunnelled through the skin and connective tissue layer to reach the blubber and muscle, which was consumed in preference to anything else. Despite being unable to feed on the carcass directly, grenadier numbers remained high until the majority of the bait had been consumed. They were believed to be preying on amphipods attracted to the food-fall. Acoustic tracking studies suggested that, although overall fish numbers remained high during this phase, individuals did not stay significantly longer at the site of the large food-fall compared to a small one, and a "conveyer-belt" of fish arrived, fed and dispersed on a scale of 10s to 100s of km. Once the soft tissue had been removed, grenadier numbers declined and mobile scavengers were replaced by a variety of more benthic fish and invertebrates, some of which took up residence amongst the bones, e.g. eelpouts and galtheid crabs. Funnel traps recovered with the carcass and from a series of fish trap deployments of varying duration indicated a succession in species composition of amphipods, with specialist necrophages such as Eurythenes gryllus and Paralicella sp. being replaced by more generalist feeders of the Orchomene species complex.