Types of whale fall

The carcass undergoes different processes depending on the depth of which it has sunk. While most whale falls undergo the 4 main stages. The timeframes of the decomposition processes and therefore biological succession very depending on size of carcass, depth, temperature and location.

            Using case studies of scientific experiments to show the variability of falls.

            An experiment conducted by Fujiwara off the coasts of Japan was the first ever-using sperm whales. The dead whales were sunk to a depth of 219- 254m and observed over a 2-year period.

            The first recorded observation of the falls’ came 18 months after their sinking. At this time no vent, seep or deep water whale species were found. However a new species of Osedax was discovered. No soft tissue remained but some blubber was still present. 2.5 years after the sinking, the bones were either buried in sediment or covered in bacteria or sessile organisms. After 3.5 years some blubber remained. However the carcass was already at stage 3 after 1.5 years. Indicating a shorter decomposition time. Therefore a faster break down of the carcass. This could be due to the effect of temperature. At deep water the ambient temp is around 4C while at the experiments site the temp was 12 C. The faster break down of shallow water whale carcass could explain their rarity. (Fujiwara et al 2007)

            Glover conducted 5 experiments sinking 4 porpoises and a fluke between 6- 30 m, however some failed before their conclusion due to equipment failure. From the entire data set he discovered that the dominant scavengers were mainly echinoderms and crustaceans. The porpoise at 6 m also had scavenging whelks. Most of the fish observed did not contribute significantly to the decomposition of the whale carcasses.

             The time taken for skeletization was much slower than the deep sea counter part. One key observation made however was that the skin took much longer than anticipated to decompose, but once the skin was removed decomposition of the flesh moved at a significantly faster pace. Stage 3 was not observed due to dispersal of the bones by tides. (Glover et al 2010)

            Dahlgren sunk 2 whales in 2006. a minke whale at 125m and a pilot whale at 30m, on the West coast of Sweden. Throughout the experiment the main scavengers were hagfish. The carcass also had evidence of shark activity, and had a large amphipod presence. The minke whale carcass was completely skeletized after 6 months showing a fast scavenger stage. However, the pilot whale remained intact for the same duration. The carcass did have some ribs and vertebrate exposed before the sinking, these exposed bones did have osedax species and bacterial mats. The theory put forth was that wave and tide action prevented fragile organisms from settling and also the rate of sedimentation is different than the deep, in shallow water the redistribution of sediment can occur very quickly. (Dahlgren et al 2006)

            The experiment by Kemp in 2006 sunk 2 porpoises, to bathyal depths of

2550- 2710m. The first porpoise was retrieved after 1 week, the second after 6 months. The experiment showed that Atlantic and Pacific have different assemblages, and that the rate of decomposition is slower in the Atlantic than in the Pacific. She also put forward that the 3 main fauna succession stages may not take place on smaller carrion due to their limited energy content compared to larger whales like blue or fin. (Kemp et al 2006)

These experiments show that whale fall assemblages differ between oceans, depths and even in time. The most notable scavenger found on the whales were hagfish. It is now thought they are responsible for being a key contributor to opening the carcass to other organisms.

            The other difference is that there is a lack of vent and seep fauna on the whales. A difference to many of the whale falls found in the Pacific including the first ever by Bruce Bennett and Craig Smith (Smith et al 1989)

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