Second Deployment 2007

The second study was conducted the following year in an almost identical manner to the first; the only differences were that the study was begun in early September, almost 1 month later than the first study, the carcass was killed by pin gun so a small head wound was present, and the carcass was weighted differently, with three separate sets of weights placed on the carcass. These were not connected, so if one weight was lost, the others would remain. The carcass was deployed at the same site as before.

As soon as the carcass was placed on the seabed, large numbers of M. quadrispina were immediately attracted. These were already present on the sea floor, but arrived in much greater numbers so were clearly attracted by the presence of the carcass. Within a few hours, the carcass was literally covered with M. quadrispina. Shortly afterwards, C. magister and P. platyceros arrived at the carcass (Fig. 12.14).

Fig. 12.13 Dissolved oxygen levels during the 2006 VENUS pig study (VENUS Project, University of Victoria)
Fig. 12.14 Three spot shrimp (Pandalus platyceros) and Dungeness crabs (Cancer magister) attracted immediately to the 2007 carcass (VENUS Project, University of Victoria)

When first turned on, the camera lights seemed to repel the C. magister and P. platyceros, although only for a few seconds, as they rapidly returned, but they seemed to acclimatize to them after a few days and later observations did not show the lights particularly attracting or repelling the macro fauna although zooplankton, in particular arrow worms, (Chaetognath, Sagitta elegans Verrill) were greatly

Fig. 12.15 2007. Zooplankton, in particular, arrow worms (Sagitta elegans Verrill), attracted by the camera lights (VENUS Project, University of Victoria)

attracted to the lights and after a few minutes of observation would almost obliterate the view (Fig. 12.15). The animals seemed to be attracted to all areas of the carcass and a small round grazed area was noted in the skin. By Day 1, 24 h after deployment, a rip had appeared in the skin in the central line of the abdomen, approximately 7 cm long. A crab was seen reaching deeply into the abdomen (Tunnicliffe 2006). The crabs, C. magister, frequently had barnacles on their carapace and the patterns of these barnacles allowed identification of some individual specimens. It was seen that the same specimens returned to the carcass repeatedly. On Day 1, the dominant fauna were P. platyceros and C. magister. Also seen, but in lesser numbers, were tanner crabs (Chionectes tanneri Rathbun).

By Day 2, tissue bulged from the abdominal rip, which had been extended, and a flap of skin had been pulled away. From this point on, the majority of animal activity was concentrated at this area (Fig. 12.16). The extruded tissue and skin were voraciously fed upon by C. magister and P. platyceros and rapidly removed (Fig. 12.17). Once the extruded tissue was removed, C. magister reached into the abdominal cavity and pulled out more tissue, organs and coils of gut. The snout area of the head had also been grazed, although this area was of much less interest than the abdominal area. Munida quadrispina feeding and picking at the head region did not appear to be able to break the skin and left only grazed areas. By Day 3, three small, round, ragged marks were seen in the side of the carcass above the abdominal area (Fig. 12.18). These are thought to be caused either by the rear legs of C. magister as they anchored themselves above the abdominal area, to feed inside the abdomen, or may have been caused by the chelicerae as they picked at the skin (Wallace 2008). These areas later became attractive themselves.

Over the following days, the abdominal rip was extended and large amounts of tissue were removed. C. magister and P. platyceros were the predominant scavengers,

Fig. 12.16 Day 2, 2007. Tissue pulled out of abdominal rip. Note squat lobster pulling at tissue (VENUS Project, University of Victoria)

Fig. 12.16 Day 2, 2007. Tissue pulled out of abdominal rip. Note squat lobster pulling at tissue (VENUS Project, University of Victoria)

Fig. 12.17 Day 2, 2007. Crabs feeding voraciously at abdominal rip (VENUS Project, University of Victoria)

Fig. 12.18 Day 3, 2007. Tears in the skin above the abdominal area, presumably caused by crab rear claws as they maintain a purchase on the tissue while reaching into the abdomen or by crabs picking at skin (VENUS Project, University of Victoria)

Fig. 12.19 Day 5, 2007. Crabs and shrimp have removed much of the internal tissue and organs and extended the abdominal rip to the sternum (VENUS Project, University of Victoria)
Fig. 12.20 Day 5, 2007. Dungeness crab (Cancer magister) and large numbers of three spot shrimp (Pandalus platyceros) feeding at abdomen (VENUS Project, University of Victoria)

with M. quadrispina also present and feeding. C. magister were seen to pursue, kill and eat the M. quadrispina on occasion. By Day 5, although little could be seen externally, clearly a large amount of tissue had been removed internally through the abdominal slit as the abdomen had an exaggerated concave appearance (Fig. 12.19). Cancer magister and P. platyceros crowded this area to feed, almost obscuring it (Fig. 12.20). Arrow worms continued to be present in large numbers. Crab chelicerae made cutting and snipping marks in the edge of the skin, and rear legs were used to anchor the crab firmly in the tissue as they rocked to pull organs out.

Fig. 12.21 Day 9, 2007. Abdominal damage extended down between back legs and organ tissue being removed (VENUS Project, University of Victoria)
Fig. 12.22 Day 9, 2007. Head region still intact, with eyeball present, although eyelid has been removed (VENUS Project, University of Victoria)

By Day 9, the abdominal damage had been extended down between the back legs and organ tissue was still being removed (Fig. 12.21), although the head was still barely damaged and the eye still intact, although the eyelid itself had been removed (Fig. 12.22). Pandalus platyceros were seen picking at the ears. The abdominal opening had been extended to approximately 20-30 cm long and 10 cm wide. The predominant fauna continued to be C. magister, M. quadrispina and P. platyceros, with Sagitta elegans frequently attracted to the lights, appearing in large clouds. On Day 10, the dominant fauna were M. quadrispina, with these seen

Fig. 12.23 Day 10, 2007. Dominant fauna are Munida quadrispina (VENUS Project, University of Victoria)
Fig. 12.24 Munida quadrispina on the head (VENUS Project, University of Victoria)

to be actively pulling tissue out of the abdominal cavity (Fig. 12.23). Large numbers of M. quadrispina were all over the carcass as well as the entire surrounding area. Some slender sole (Lyopsetta exilis) were seen to swim over the carcass but showed no interest in the carcass itself. Such fish were seen on and around the carcass throughout the study. Over the following days, as oxygen levels dropped, M. quadrispina were still seen in large numbers, but much fewer C. magister and P. platyceros were present, although these were still seen in lower numbers (Fig. 12.24). On Day 11, C. magister were seen removing pieces of tissue from between the back legs and two circular areas of feeding damage could be seen on the hock region of the rear legs (Fig. 12.25).

Fig. 12.25 Day 11, 2007. Dungeness crab Cancer magister removing tissue from between back legs and abdominal region. Grazing circles seen on hocks (VENUS Project, University of Victoria)
Fig. 12.26 Day 12, 2007. Rib ends now exposed. Laser lights indicate 10 cm distance between lights. Note remains of squat lobster (Munida quadrispina ) eaten earlier by Dungeness crab (Cancer magister) (VENUS Project, University of Victoria)

By Day 12, the cartilaginous ends of the ribs were exposed (Fig. 12.26) and feeding continued all over the carcass including the head end. Munida quadrispina were seen going into the abdominal cavity and pulling out parts of organs. On Day 14, small gammarid shrimp (Family Lysianassidae), Orchomenella obtusa (Tunnicliffe 2006), were first seen on the exposed tissue of the back legs and ropes nearby (Fig. 12.27). These increased greatly in numbers and began to cover the carcass several mm deep by Day 17 and Day 18, concentrating on areas of exposed

Fig. 12.27 Day 14, 2007. Small gammarid shrimp (Orchomenella obtusa, Family Lysianassidae) first seen on carcass (VENUS Project, University of Victoria)
Fig. 12.28 Day 18, 2007. Large numbers of Orchomenella obtusa on remains (VENUS Project, University of Victoria)

muscle and tissue (Fig. 12.28). Such amphipods are often seen by public safety divers when recovering bodies and are colloquially referred to as "sea lice" (MacFarlane 2001; Teather 2000). Both M. quadrispina and P. platyceros were seen to feed on the small amphipods as well as on the tissue. Cancer magister, M. quadrispina and P. platyceros continued to feed and extended the opening at the abdomen to expose more ribs, although as oxygen levels were low at this time, and remained below 1.0mL/L, the dominant fauna remained M. quadrispina. The skin remaining on the torso appeared to be "rucked up" as if it were a shirt with little

Fig. 12.29 Day 18, 2007. Lower part of pig has been completely removed. The skin appears loose below the rope line (VENUS Project, University of Victoria)

connection to the tissue underneath, suggesting that much of the tissue underneath had been removed. The skin itself remained intact, and hair could still be seen to be present.

Between the evening of Day 17 and the morning of Day 18, the lower half of the pig was removed completely, leaving just the upper part of the remains in sight of the camera (Fig. 12.29). As the camera tripod is static, it was not possible to determine whether the lower half had simply been removed a few metres out of camera view, had been taken a distance away or had been consumed. No clear mark was left as the remains were already extensively scavenged, but it seems likely that the culprit was as suspected before, the sixgill shark (Hexanchus griseus), which took not only part of the remains but also dragged the rope and chain from the lower body out of camera range. When the remains were recovered 5 months later, no sign of the lower body, or the lower body weights were recovered despite an extensive search of the surrounding area. As the remaining weights were still attached to the upper part of the remains and not interconnected to the other weights, the rest of the carcass remained in sight of the camera for the duration of the experiment, although the carcass had been dragged about 30 cm. The skin on the remaining part of the carcass appeared to be moved further up the remains, as if it were a loose shirt.

By Day 22, the skin was wrinkled over the entire area of thorax, neck and head as if no muscle or tissue lay beneath (Fig. 12.30) suggesting that all the tissue beneath had been removed by animal action. Large numbers of O. obtusa were present on the areas of skin that had been pulled back and large numbers of M. quadrispina were present, feeding on the remains as well as the small shrimp. Cancer magister and P. platyceros were present at times, although in lesser numbers. By the next day, the lack of tissue beneath the skin was confirmed as the majority of the skin had been pulled over the head like a sweater, revealing a clean,

Fig. 12.30 Day 22, 2007. Tissue beneath skin has been removed and skin now appears to be lying directly on bones, with most of tissue removed (VENUS Project, University of Victoria)
Fig. 12.31 Day 23, 2007. The skin has been pulled up above the head to show that the remains beneath are clean bones with almost no tissue attached. (VENUS Project, University of Victoria)

fully articulated skeleton with cartilage intact (Fig. 12.31). In the subsequent few days, the entire skin was pulled over the head of the carcass and torn apart by M. quadrispina, with pieces of skin being pulled in different directions by large numbers of these animals (Fig. 12.32). As the skin was pulled further, the skull was also shown to be completely skeletonized (Fig. 12.33). At this time, the only animals on the carcass were M. quadrispina. In the following days, the rest of the skin was consumed, with the last piece of recognizable tissue being the ears. Once only bones were left, M. quadrispina removed the cartilage from the end of the ribs and scapula, gradually disarticulating the bones. Although some P. platyceros were still

Fig. 12.32 Day 24, 2007. Munida quadrispina removing remaining tissue from bones (VENUS Project, University of Victoria)
Fig. 12.33 Skin pulled from skull revealing skeletonized skull and mandible (VENUS Project, University of Victoria)

present in low numbers on the carcass, no C. magister remained, and once the skin was gone, no O. obtusa were noticed. A bacterial mat began to form on the bones after skeletonization. Most of the cartilage had been removed by Day 42. The bones were recovered 5 months after submergence and are undergoing further study.

The levels of dissolved oxygen in the water were much lower in this second study, with levels of 1.4 mL/L at the start of the study, which dropped below 1mL/L by Day 4, and continued to drop to 0.1-0.4 mL/L for the latter part of the study (Fig. 12.34). Temperature rose from 9.3°C to 9.42°C in the first few days then remained at a constant 9.4°C.

Fig. 12.34 Dissolved oxygen levels during the 2007 VENUS pig study (VENUS Project, University of Victoria)
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