Friday, 16 October 2009

Porpoise encounter

Norfolk’s extensive coastline offers a fair number of opportunities for seawatching, an increasingly popular pastime among local birdwatchers. Hunkered down on a blustery autumn or winter morning and scanning with binoculars for passing seabirds that have been driven close to shore by the stiff winds, it is hard but sometimes rewarding work. Identifying distant birds, as they dip and rise between the waves, is something of an art form and I still have much to learn. The worse the weather, the harder it is to identify passing birds but the harshest weather often delivers some of the best birds close inshore.

Seawatching earlier in the year, under the calmer conditions of early autumn, can be more rewarding in that you tend to getter better views of things and don’t have to endure such biting winds. The other weekend we spent an hour or so seawatching at Winterton. It had been a quiet morning in the dunes for passage migrants (save for the Red-breasted Flycatcher skulking in some thick scrubby cover) and we decided to see what the sea could offer. In addition to numerous Cormorants, passing flocks of Eider and Common Scooter, there was the rewarding sight of a Harbour Porpoise making its way slowly south just 200m off the beach.

The Harbour Porpoise is our smallest cetacean (whale or dolphin), measuring in at about 1.5m in length. Less boisterous than a dolphin, the Harbour Porpoise only rarely leaps from the water, instead moving with a rolling motion, the small triangular dorsal fin just clearing the water’s surface on a round back. When the sea is much rougher they may surface rapidly, which can result in them clearing the water to breathe. Most are seen singly or in small groups of 2-10 individuals and they can be highly mobile. Satellite tracking studies have revealed that the males range further than the females and can easily cover more than 50km during the course of a day. Although they are present in our waters throughout the year, sightings tend to peak between July and October, which may either reflect recording effort or a genuine seasonal pattern to the use of our coastal waters.

Numbers are likely to have changed over longer periods of time as well, as changes in fish stocks, increasing levels of disturbance and increases in sea temperature influence distribution and population size. Unfortunately, there is a great deal still to learn about Harbour Porpoises and our lack of knowledge leaves them open to various threats (such as fisheries bycatch). Because of this sightings are urgently needed; if you see a porpoise around the East Anglian coast download a recording form from the reports and publications section of and make your sighting count.

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