Seal (42K
JPEG image) The South-West Wales coast supports a breeding colony of the grey seal Halichoerus grypus. During the breeding season the seals are concentrated around the islands and certain remote mainland shores. Pupping takes place during autumn, followed by mating and moulting through the winter. The population then disperses more widely, and young and adult seals can be found foraging for food across a large sea area, offshore, on the open coast and in estuaries. Only small numbers of seals remain within the breeding areas during spring and summer.
Seal (42K
JPEG image)
Seals are very vulnerable with respect to oil pollution in that they have to spend much of their time at the surface of the water. They need to surface every few minutes to breath. They regularly haul out on to beaches. During the course of an oil pollution incident they are at risk both when surfacing and when hauling out.
The Sea Empress ran aground close to the Pembrokeshire seal breeding area. Fortunately, the spill took place at a time when last year's pups and many adults were widely dispersed. Unfortunately, the oil slicks also became widely dispersed, increasing the likelihood of seals encountering oil. Another important consideration was the spraying by aircraft of chemical dispersants on to slicks at sea during the clean-up operation. Many tonnes of chemicals were deployed in this way. Seals may have encountered chemicals during spraying operations or when in contact with previously treated slicks.
Observations made within the Skomer Marine Nature Reserve, which is a seal breeding area, revealed that a proportion of the seals resident during the period of severe oil pollution did show some degree of oiling on their coats. In a few cases the oiling was heavy. No evidence of pollution-related seal mortality was identified during the incident. It is, however, quite possible that seals may have experienced short-term pollution symptoms such as eye or respiratory tract irritation. Longer term health problems may manifest themselves in due course. One possibility may have involved effects arising from the concentration of toxins through the food chain - grey seals consume a variety of prey including crabs and fish.
The South-West Wales region is also frequented by common porpoises Phocoena phocoena and bottle-nosed dolphins Tursiops truncatus. The impacts of the oil and chemical pollution on these species remained unknown. Significant numbers of both species, however, were sighted within the waters of the Skomer Marine Nature Reserve during spring and summer of 1996.
University of Wales Swansea School of Biological Sciences Home Page
Authors: Peter Dyrynda, Rob Symberlist
Contributor: B. Bullimore (Skomer Marine Nature ReserveWarden, CCW)
Contact: P.Dyrynda@swansea.ac.uk
Update: 22/4/02