It’s important for forensic teams and police to know the gruesome ins and outs of how bodies decompose in different circumstances. But we know surprisingly little about how fleshy bodies fair when they are submerged at sea.
In a bid to better understand how organisms decompose for forensic and criminal investigations, criminologists from Simon Fraser University and the Ocean Network Canada's Victoria Experimental Network collaborated by submerging pig carcasses in an underwater cabled laboratory in the Salish Sea, using remotely operated equipment to carry out experiments. The study was recently published in PLOS ONE.
The researchers conducted two experiments, one in spring and one in autumn. Their research showed that a whole pig carcass can be stripped to the bone within three days during the autumn. During spring, the carcass reached this state by day four.
The experiment used large pig carcasses due to their similar size and structure to a human body. They were placed 300 meters (1,000 feet) below the surface onto the seabed in the Strait of Georgia, a highly oxygenated strip of water between Vancouver Island and the west coast of Canada.
"Earlier studies in Saanich Inlet (100 meters [330 feet]) and Howe Sound (7 to 15 meters [23 to 49 feet]) indicate that a carcass approximating a human body in torso size, skin type, and internal bacteria would be likely to survive for weeks or months, depending on oxygen levels, season, depth and whether it remained in contact with the seabed," criminologist and lead author Gail Anderson said in a statement.
She added, "However we've found that in highly oxygenated deeper water, it can be expected that such a body would be skeletonized in less than four days, although bones could be recovered for six months or more."
In both seasons, tiny shrimp called Lyssianassid amphipods were immediately attracted to the body. During the spring, this was followed hours later by several bluntnose sixgill sharks. The sharks bit off parts of the pig, but appeared to stop biting after the 24-hour mark, despite there still being meat left. Thousands of these amphipods continued to build up in numbers throughout all of the days, even covering parts of the cage and surrounding area.
On day nine in spring, a giant pacific octopus (Enteroctopus dofleini) approached the carcass and appeared to curiously inspect the remains, although it appeared not to eat any. The following day in spring, the bones were then visited by spot shrimp, which picked the remaining cartilage from the bones.
After 166 and 134 days of the spring and fall experiments respectively, the remaining bones were recovered by the team.
The researchers appeared surprised by how different the results were depending on the oxygen levels and depth of the water. The rapidity of the decomposition was all thanks to more activity from scavengers, as opposed to internal bacteria which has been seen more in the other studies.
Anderson noted their observations were important for recovery divers so that they know what to expect and what to search for. "When bodies or body parts are recovered, such information may also be valuable in estimating a minimum submergence time and indicating types of waters or habitats to which the remains may have been exposed," she said.