Abstract
Pig carcasses, as human proxies, were placed on the seabed at a depth of 300 m, in the Strait of Georgia and observed continuously by a remotely operated camera and instruments. Two carcasses were deployed in spring and two in fall utilizing Ocean Network Canada’s Victoria Experimental Network under the Sea (formerly VENUS) observatory. A trial experiment showed that bluntnose sixgill sharks could rapidly devour a carcass so a platform was designed which held two matched carcasses, one fully exposed, the other covered in a barred cage to protect it from sharks, while still allowing invertebrates and smaller vertebrates access. The carcasses were deployed under a frame which supported a video camera, and instruments which recorded oxygen, temperature, salinity, density, pressure, conductivity, sound speed and turbidity at per minute intervals. The spring exposed carcass was briefly fed upon by sharks, but they were inefficient feeders and lost interest after a few bites. Immediately after deployment, all carcasses, in both spring and fall, were very rapidly covered in vast numbers of lyssianassid amphipods. These skeletonized the carcasses by Day 3 in fall and Day 4 in spring. A dramatic, very localized drop in dissolved oxygen levels occurred in fall, exactly coinciding with the presence of the amphipods. Oxygen levels returned to normal once the amphipods dispersed. Either the physical presence of the amphipods or the sudden draw down of oxygen during their tenure, excluded other fauna. The amphipods fed from the inside out, removing the skin last. After the amphipods had receded, other fauna colonized such as spot shrimp and a few Dungeness crabs but by this time, all soft tissue had been removed. The amphipod activity caused major bioturbation in the local area and possible oxygen depletion. The spring deployment carcasses became covered in silt and a black film formed on them and on the silt above them whereas the fall bones remained uncovered and hence continued to be attractive to large numbers of spot shrimp. The carcass remains were recovered after 166 and 134 days respectively for further study.
Highlights
The fate of a human body in water is not well understood
The sharks did not bite the carcasses after 24 h still swam over the carcasses until they lost interest 48 h after submergence, by which time both carcasses were covered in thick layers of amphipods
All carcasses were immediately attractive to lyssianassid amphipods, including the preliminary carcass which was rapidly consumed by bluntnose sixgill sharks
Summary
The fate of a human body in water is not well understood. A great deal of research has been conducted on carcass decomposition and insect colonization in a variety of terrestrial habitats worldwide [1,2,3] yet little work has been performed in the ocean. The inaccessibility of the marine environment makes such work challenging, yet the large number of commercial accidents, recreational deaths and body depositions which occur in the ocean, make it an important area of research concerning both the ecology of death itself, and of concern here, forensic investigations of deaths in the ocean Large carcass falls such as those of whales [4,5,6,7,8,9,10], sharks [11] and porpoises [12], as well as those of large extinct animals [13,14,15] and even invertebrates [16, 17] have been studied but many of these aquatic mammals decompose in a manner very different from that of humans or human-sized mammals. Much of our knowledge of human decomposition in the ocean comes from anecdotal reports of individual body recoveries [18,19,20,21,22]
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