First Deployment 2006

The carcass sank immediately, and at no time showed any evidence of bloat or re-flotation (Fig. 12.1). A large herring ball (Clupea sp.) was present when the pig was deployed but showed no interest in the carcass. However, a number of arthropods showed immediate interest. Squat lobsters (Munida quadrispina Benedict, Family Galatheidae) arrived in large numbers and squads of M. quadrispina were seen marching across the sand towards the carcass. The M. quadrispina picked at all areas of the carcass, but particularly at the face and nose (Fig. 12.2). Three spot shrimp (Pandalus platyceros Brandt) and Dungeness crabs (Cancer magister Dana.) were also immediately attracted and picked at the carcass and at the silt that had settled on it. By Day 1, M. quadrispina, C. magister and P. platyceros were feeding at all the orifices and the carcass was moved and rocked

Fig. 12.1 Pig carcass placed at a depth of 94 m in August, in Saanich Inlet, British Columbia, Canada, 2006 (VENUS Project, University of Victoria)

Fig. 12.2 Squat lobsters (Munida quadrispina) attracted to the face of a pig carcass at a depth of 94 m, 2006 (VENUS Project, University of Victoria)

Fig. 12.3 Day 3 post submergence 2006. A probable sixgill shark (Hexanchus griseus) bite in the rump of the carcass became a major site of attraction (VENUS Project, University of Victoria)

on occasion by the crab activity. On Day 2, the pig had been moved 1.5 m and 180o from its original position, a large piece of flesh had been removed from the hind quarter and a flap of skin and tissue from the stomach had been laid open (Fig. 12.3). The culprit was not observed, but the shape, size and pattern of the bite mark indicate that it was probably caused by a sixgill shark (Hexanchus griseus Bonneterre) (Tunnicliffe 2006). From this moment on, the majority of feeding activity and invertebrate attraction was centred on this area (Anderson 2008). The main invertebrate species on the carcass were M. quadrispina which fed on the

Fig. 12.4 Dungeness crabs (Cancer magister.), squat lobsters (Munida quadrispina) and three spot shrimp (Pandalus platyceros) feed at the bite area in the rump of a pig carcass on Day 4 post submergence 2006. Lasers indicate 10 cm between light spots (VENUS Project, University of Victoria)

carcass in large numbers. A separate study done at the same time as the 2006 VENUS experiment showed that the density of the scavenging organisms, in particular, M. quadrispina increased when the carcass was present, with an M. quadrispina density of up to 1.6 per dm2 when the carcass was present but only up to a maximum of as 0.7 per dm2 when it was not (Peters 2007).

The lights did not seem to have a large impact on either attracting or repelling invertebrates to the carcass, as observed by the camera, although it is likely that the lights did impact the fauna as divers in the earlier experiments did report attraction to their lights (MacFarlane 2001).

Over the subsequent few days, the major fauna on the carcass were consistently M. quadrispina, P. platyceros and C. magister, which were seen to be eating the tissue and hollowing out the inside of the carcass from the wounded area (Fig. 12.4). Large numbers of all three species were seen on the carcass and camera scans of the surrounding area showed these species being actively attracted, moving towards the remains. Cancer magister were capable of rocking the entire carcass, and removed large pieces of tissue and organs from the remains. Munida quadrispina still showed an interest in the head region although little damage was observed. They were seen feeding on the carcass but also sifting through the fine layer of silt on the carcass. However, the majority of the M. quadrispina were seen at the wound. Pandalus platyceros fed at the wound and also on the inside of the flap of skin removed from the stomach region (Fig. 12.5).

By Day 5, a large amount of tissue had been removed from the hind quarters and the abdominal cavity had been opened (Anderson 2008). The spinal column and the intestines were exposed and C. magister, M. quadrispina and P. platyceros continued to dominate the carcass (Fig. 12.6). The fauna on this carcass was distinctly different

Fig. 12.5 Three spot shrimp (Pandalus platyceros) feeding on tissue 2006 (VENUS Project, University of Victoria)
Fig. 12.6 Day 5, 2006. Spinal column and intestines exposed. Dungeness crab (Cancer magister), three spot shrimp (Pandalus platyceros) and squat lobsters Munida quadrispina dominate (VENUS Project, University of Victoria)

from those seen on the shallower carcasses, with much lower diversity but much greater numbers of individual specimens present. In some cases, the M. quadrispina, C. magister and P. platyceros almost obscured the carcass. A small sunflower sea star (Pycnopodia helianthoides) was observed on Day 6, but larger specimens such as those observed on the shallower carcasses, were never observed. A ruby octopus was also briefly attracted on Day 6 (Octopus rubescens Berry). Tissue continued to be removed from the hind end, but although M. quadrispina were seen picking at the face and ears, very little damage was observed on the head.

Fig. 12.7 Day 8, 2006. Much of the hind quarters have been removed (VENUS Project, University of Victoria)

By Day 8, the hind quarters of the carcass had almost been removed and the back legs were partially eaten (Fig. 12.7). As most of the hind quarters had been removed, this meant that the rope securing the carcass to the weights, keeping it in camera view, had mostly slipped off the carcass. As the rear set of weights were attached to the front set by rope, this meant that all the weights were compromised and no longer kept the carcass in one spot. Therefore, the carcass was moved by animal activity several times from this point on, probably by C. magister as these were seen to rock the carcass almost over at one point. By Day 10, the rear third of the carcass was mostly reduced to bones and cartilage with some soft tissue still adhering and the lowest rib was exposed. Cancer magister were seen reaching into the cavity and tearing out flesh. Any tissue dropped by C. magister was eaten rapidly by waiting M. quadrispina. In some cases, C. magister would eat the M. quadrispina.

Cancer magister, M. quadrispina and P. platyceros were present day and night. Despite the rapid removal of tissue from the rear end of the carcass, the rest of the carcass, including face, ears and front legs appeared to be completely intact (Fig. 12.8). By Day 11, C. magister had begun to feed at the abdominal region, further up the torso. By Day 13, the carcass had been pulled free of the weights and ropes. For the first time, small red amphipods (Orchomenella obtusa Sars) were seen in small numbers on the exposed tissue of the carcass. By Day 14, the rear half of the carcass was almost entirely skeletonized, with very little tissue holding on the rear left leg (Fig. 12.9). The carcass had been moved several times and was now partway past one of the tripod legs, making viewing the front half of the carcass difficult. Cancer magister, M. quadrispina and P. platyceros continued to dominate the fauna, although several fish including slender sole (Lyopsetta exilis (Jordan and Gilbert)), herring and dogfish, swam through the area, apparently showing little interest.

Fig. 12.8 Day 11 2006, the rear third of the carcass was mostly skeletonized but the upper torso, front legs and head, were still intact (VENUS Project, University of Victoria)
Fig. 12.9 Day 14, 2006. Rear half of carcass is skeletonized, and carcass is no longer restrained by weights so has been pulled away from camera. (VENUS Project, University of Victoria)

By early on Day 15, the carcass had been moved further away and the snout region showed some evidence of feeding, although the upper body remained mostly intact. A single bone was seen near the carcass, but the rest of the carcass remained articulated. Later that day, the carcass was moved a further 30 cm and was now lying outside the tripod area. The left rear leg had been disarticulated and was lying close to the carcass (Fig. 12.10). By Day 16, the carcass had been completely turned around and the only animals seen were large numbers of M. quadrispina which were feeding on both the main carcass and the disarticulated leg (Fig. 12.11). Some feeding damage could now be seen on the face, with the eye socket empty

Fig. 12.10 Day 15, 2006. The carcass has been dragged completely out of the tripod area and one leg has been disarticulated (VENUS Project, University of Victoria)

Fig. 12.11 Day 16, 2006. Carcass has been turned 180°. Some feeding damage now seen on face. Disarticulated leg is still present. Only macro fauna are squat lobsters, Munida quadrispina (VENUS Project, University of Victoria)

and the upper part of the nasal bones exposed. In general, however, the upper body was intact, with skin and hair present, whereas the lower half of the remains was skeletonized. On Day 20, the carcass was again turned around (Fig. 12.12). Most of the rear part of the carcass was gone, with both legs and pelvis detached and only the lower part of the spinal column remaining. One femur had been picked clean and was still in camera range. By Day 22, the bulk of the carcass had been removed from camera range and by Day 23, only a single femur remained in range.

Fig. 12.12 Day 20, 2006. Carcass has again been turned 180°. Pelvis and remaining rear leg gone (VENUS Project, University of Victoria)

For the duration of the experiment, by far the most common animals on the carcass were C. magister, P. platyceros and M. quadrispina. At no point were any signs of classic decomposition observed and biomass removal appeared to be entirely due to animal activity. In November, a search was made for any remaining bones but none were recovered.

The levels of dissolved oxygen in the water were around 2.1 mL/L at the start of the study in early August and dropped slowly over the subsequent days to lows of 0.2 mL/L and means around 0.7 mL/L/ (Fig. 12.13) (Anderson 2008). Salinity remained stable throughout the experiment at 31 PSU (Practical Salinity Units), and temperature remained constant around 9.5-9.8°C.

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