February Meeting – Marine Mammals – Janet Preece

February 15th, 2011

Janet took us through a range of mammals that can be classed as ‘marine’, from polar bears to whales via sirenians, otters, dolphins and – her particular favourite – seals.

Mammals have problems adapting to life in the marine environment, not least of them insulating themselves against the chilling effect of the water on their warm blooded bodies. While most marine mammals rely on a layer of fat to help keep them warm, we learnt that not only is the sea otter the smallest marine mammal, it is the only one that relies solely on its fur for insulation, having the densest fur in the animal kingdom. It’s probably the only tool user too: they often use a rock to break open shellfish, lying on their backs in the water with the shellfish on their chests and pounding down with the rock.

As well as the problems of keeping warm marine mammals have all the problems of being air breathing animals in a watery environment, tied to maintaining contact with the surface, and with a range of breeding strategies to cope with this. They have also reached differing levels of adaption to moving through water; some being fully aquatic, and others needing to return to land.

We skimmed on past whales, dolphins, and porpoise to concentrate on Janet’s favourite animals – seals.

Both species of seals we have in this country are true seals, as opposed to the sea lions and fur seals, and the walruses. True seals are more adapted to the water than the other two groups but are still tied to the land.

Our two species are the harbour (or common) seal Phoca vitulina, and the grey seal Halchoerus grypus. We have significant proportions of the world populations of both species in our seas, which makes them globally significant.

Janet covered some of the threats to seals and other marine life in general. One of the most shocking was the ‘corkscrew killer’, where animals have been found with deep wounds spiralling along their bodies; the most likely explanation for this being that the animals have been caught in a ‘ducted’ propellor. Other threats included all the usual suspects – pollution, plastic bags and ballons, discarded fishing gear, hunting, and the effects of overfishing on the food chain.

Some great pictures and stories of seal encounters around the Farnes reminded me of some of my own seal encounters around the Farne Islands and others. I haven’t got any Janet’s pictures but some of my pictures are at –
http://www.zen102367.zen.co.uk/diving/farnes0806.htm

A selection of interesting facts that I picked up on the way –
If you find a dolphin or porpoise stranded on the shore it can be difficult to tell the difference; but if you look at the teeth, dolphins have conical shaped teeth and porpoise have spade-like teeth.
Walruses use the “squirt and suck” method of feeding (I can’t remember exactly how it works but I just love the way it sounds!).
Whales make footprints. Their skin is oily and the tail will leave an oily ‘print’ on the surface of the water as they dive.

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