11 March 2013

Learning from an unusual visitor

Pygmy sperm whale stranded at Aphrodite Beach
Walvis Bay (from the old German name 'Walfischbai', meaning whale bay) is living up to its name. On March 10th, a pygmy sperm whale was found in the shallows on Aphrodite Beach, between the towns of Walvis Bay and Swakopmund, Namibia.

Despite their names, pygmy sperm whales (Kogia breviceps) and dwarf sperm whales (Kogia sima), which look so similar that they are impossible to distinguish without measuring the relative proportions of the body, are in fact more closely related to dolphins than whales. They share many features with true sperm whales, although they are small (maximum lengths of 2.7m for dwarf and 3.3m for pygmy) in comparison - sperm whales can reach over 18 m in length. Like sperm whales, they have teeth (rather than the baleen of true whales), but only in their lower jaw. Dwarf and pygmy sperm whales also have a spermaceti organ in their head, as do sperm whales. This organ contains the spermaceti wax that was once sought-after by whalers; the wax was used to make candles and in cosmetics, leatherworking and as a lubricant. 

Much like the pygmy right whale that stranded last month in Walvis Bay, pygmy and dwarf sperm whales are shy creatures, difficult to spot at sea. This, my first encounter with a Kogia whale, was a fascinating opportunity to see an odd-looking creature from the depths. Thought to be inhabitants of deep, offshore waters, these whales are known to feed on squid and crustaceans (such as shrimp and crabs) that live on the sea floor. Their tiny, underslung lower jaw is designed to facilitate this type of feeding. Both species have blunt, square heads and a recurved dorsal fin, which is closer to the tail in pygmy sperm whales, and closer to the middle of the back in dwarf sperm whales.

This encounter was also a reminder of the difficult truths faced sometimes by those who attend to stranded whales and dolphins. The pygmy sperm whale was alive, but in very bad condition. A head-on view allowed an assessment of its body condition; it was visibly emaciated, obvious from the sloping flanks on either side of its backbone. As well as scrapes and cuts sustained during its hours in the shallows and on the beach, the whale's body was covered in fresh bites from cookie-cutter sharks, and one eye was damaged. The members of the public who had tried so hard to refloat this whale for several hours before I arrived, had noted how it rolled in the waves, apparently unable to stay upright and with little ability to swim. 
Head-on view shows the sloping flanks, a sign of emaciation.

Strandings networks worldwide aim to assist any healthy whale or dolphin to return to sea, where possible. In the case of an animal which is visibly unhealthy, however, repeated refloatation attempts are more a comfort to the humans involved than a help to the whale. Sometimes, a whale or dolphin strands because it is no longer physically able to navigate or swim, perhaps due to old age or disease, and then it does no good to return the animal to the sea. In this case, Strandings Network personnel made the difficult decision to let time take its course, and as the sun dropped below the heavy clouds on the horizon, we left the beach.

The whale died overnight. This morning, before the carcass was removed by the Municipality, the Namibian Dolphin Project team returned to the beach to collect some scientific data from this rare species in the hope that, through research, we can learn more about these enigmatic inhabitants of Namibia's seas. Each stranded animal, alive or dead, brings with it a little more insight into their underwater world.

Thanks, as always, to Neels and Megan Dreyer for their unfailing interest in and help with stranded cetaceans.

1 comment:

Niamh said...

So sad to read Ruth! But I suppose these difficult decisions have to be made. x