The status of grey seals (Halichoerus grypus) at Lundy, 2008-2009
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- Introducing the historical use of sites by seals in SW England
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- Introduction to grey seals
The status of grey seals (Halichoerus grypus) at Lundy, 2008-2009Stephen Westcott. stephenwestcote@yahoo.co.uk ContentsSummary Introduction to Lundy Introduction to grey seals Introducing the historical use of sites by seals in SW EnglandIntroducing the seals at Lundy in the UK context 1. Aims 2. Methods 3. Health and safety protocol
4.1 Pup production 4.2 Pup mortality 4.3 Moulting 4.4 Abundance & distribution 5. Discussion 5.1 Pup production 5.2 Pup mortality 5.3 Abundance & distribution 6. Acknowledgements 7. References
9. Managing impacts and potential impacts Tables: 1: Lundy sites where pups were born, August 2008 – June 2009 2: Lundy sea cave sites where pups were born, August 2008 – June 2009. 3: Lundy beach sites where pups were born, August 2008 – June 2009 SummaryGrey seals use Lundy sites the year round in numbers that appear to vary little from month to month. It is likely that seals present at any time number around 125 individuals, with females outnumbering males. Annual pup production, currently, appears to be 40 – 45, probably varying from year to year according to sea conditions. Firstborn pups are most likely to be located in west coast sea caves and clefts. Later born pups appear on remote beaches. The season of pup production extends from late August to mid-October, with a small number of pups born outside that period (until late January, in this survey). The annual moult takes place between December and March. At present, seals when hauled out are not subject to much disturbance because the sites they use are difficult to access from the land. However, there are many reports of seal-diver interactions that, evidently, reflect seal curiosity about divers as much as vice versa. Some reports suggest that female divers when experiencing menstruation are subject to oppressive harassment from seals. Future seal studies should be mounted from Lundy so as to take best advantage of weather windows. Introduction to LundyLundy is an island situated, in effect, at the frontier between the Atlantic Ocean and the Bristol Channel, at 51°10’ North, 4°40’ West. It is situated in an area that is known to some as the Severn Sea, some 11 miles NNW of Hartland Point, Devon and 33 miles south of the south Wales coast. It rises as a cliff-girt island massif about 375 feet above sea level. The top of the island resembles a gently undulating plateau above the high and often steep cliffs. It measures approximately three and a half miles in length by about a half-mile in width and is orientated (approximately) north - south. It has an area of 852hectares. The west coast is exposed to the predominantly southwesterly winds and to the full power of the Atlantic waves. As a consequence, storm beaches have been formed at the back of some sea caves. Strong tidal races scour the north and south coasts of the Island. Although both north and south coasts are exposed, the south coast does include beaches where refuge can be taken. The east coast is relatively sheltered. It has several (mainly boulder) beaches. There are very few places where relatively easy access to the sea can be achieved from the top of the island. The easiest access to the sea is achieved via the road down to the jetty in Landing Bay, at the SE corner of the island. There are steps down to a very small platform near the lighthouse at the north end, by Kittiwake Gully, and there is a more difficult track with some steps at Montagu’s Steps, near the SW point of the island. The island is owned by the Landmark Trust. In 1986, Lundy was designated the first statutory Marine Nature Reserve in the UK. It includes the foreshore as well as the coastal waters of Lundy. Access to Lundy by sea is achieved via the MV Oldenburg, which operates from Ilfracombe or Bideford between late March and October, or via a boat service operated from Clovelly. Access to Lundy by air can be achieved via a helicopter service operating from Hartland, while a small number of people kayak across from the mainland. Introduction to grey sealsGrey seals are the larger of the two species of seal that breed in the British Isles. If weight is the criterion used, they are the largest wild mammals breeding ashore in the British Isles, adult males growing to 350kgs while females grow to 250kgs. Males may live for up to 25 years, females up to 35 years, according to current knowledge. Males are believed to breed from the age of 10, females breed from the age of 3-5 onwards. Grey seals occur in three main groupings only in the temperate and Arctic seas of the North Atlantic: on Sable Island and the east coast of Canada, in the Baltic Sea and in the NE Atlantic between Russia, Norway and Iceland in the north and Brittany, SW Britain, Eire and the Wadden Sea in the south. Among the seals of the world, they are relatively uncommon, the total population being less than half a million. In recent years, estimates of the numbers of grey seals occurring in the various regions of Britain have come to be regarded as being subject to uncertainty. However, UK grey seal numbers are believed to represent 45% of the world population and 85% of seals born in the NE Atlantic outside the Baltic Sea. A recent point estimate for the number of adult seals occurring in the UK is 133,000. Of these, more than 90% occur at Scottish sites – especially the Western and Northern Isles (SCOS Main Advice 2007, SMRU). The Sea Mammal Research Unit (SMRU) has done minimal work in SW England and Wales and so is not in a position to offer an accurate estimate for the numbers of pups born annually. However, they propose an estimate of 1750 pups born in SW England and Wales, based on work carried out for the Countryside Council for Wales (CCW) and Natural England (NE), with the trend being an ‘increase’ in the population size. SMRU survey visits to discover pup production in SW Britain are almost non-existent, with even these few being rendered unsuccessful by a combination of the sea conditions they encountered as well as by their lack of knowledge as to the location of nursery sites (e.g. Prime, 1985) and the timing of the season of pup production. No record has been found of any visit by SMRU to Lundy. In the British Isles, the seals breeding at SW Britain sites (Cornwall, the Isles of Scilly, Devon, Wales, the Isle of Man) and Brittany are currently recognised as being genetically distinct from those using Scottish sites. Studies by Thompson and others have shown that individual grey seals exhibit varying behaviours. For example, some forage several hundred kilometres from their ‘fishing station’ in trips that last for several days. Many forage no more than 100kms from the haul-out site they are using as a base. Other studies (McConnell et al, 1992) have shown that some but not all seals move from one locality to another during the course of a year, for reasons including using another foraging area, or in order to engage in breeding activity. Grey seals may spend between 85-90% of their lives in the sea. These discoveries have implications for how we should regard the seals that use Lundy sites. Indeed, rather than seeing the ‘seals of Lundy’, rather we should regard the seals as belonging to a NE Atlantic sea area that comprises the Irish Sea, the Celtic Sea, the Western Approaches, la Mer d’Iroise (off west Brittany) and the English Channel. Introducing the historical use of sites by seals in SW EnglandGrey seals have used sites along the coasts of southwest England perhaps for longer than have human beings. They have always used sea caves, remote beaches, islands and skerries for hauling out. They have always used the adjacent waters to such sites as water resting places. They have always ventured into estuaries. During the ice ages and in the northerly parts of their range, they would have hauled out on to the ice at the water margins as they do today in the Arctic. Their remains have been found in Bronze Age middens in the Isles of Scilly. They would have been one of the principal target species of the earliest hunters. The earliest and most illuminating historical record of seals was made by Carew in his Survey of Cornwall (1602). In this manuscript, he made the earliest written reference for the region to the fact that they used sea caves: ‘They also come on land and lie sleeping in holes of the cliffe…’ ‘Hole’ is a Middle English word used for ‘cave’ (‘Ogo’ is the (Celtic) Cornish word for ‘cave’). The significance of this evidence is that the use of sea caves has been a long-term phenomenon. In effect, they have ‘always’ done it, even at a time – four centuries ago – when the southwest England coasts were infinitely less accessible to people than they are today. Dr. William Borlase also made reference to cave use by seals in ‘The Natural History of Cornwall’ (1758): ‘It is common in the caves and on shores of Cornwall which are least frequented…’; and again, in 1763, he wrote: ‘The narrow beach in the innermost parts of the caves afford resting-places for the seals and nurseries for their young’. The 1763 memoir contains the first recorded reference to the use of sea caves as nursery sites as well as resting-places. There is a fleeting glimpse into long-term use by seals of specific sites offered in 1667 by John Rae: ‘On the rock called the Longships they often, in calm weather, find the phocae, which they call soiles, sleeping…’ Grey seals were not distinguished accurately from other seal species using British waters until the nineteenth century, so the elegant reference to phocae should not here be taken to refer to the harbour (or common) seal, Phoca vitulina, which occurs historically and currently only as an occasional visitor to the waters of southwest England. Nevertheless, it should be noted that the Longships site remains one of the principal haul-out sites used by the seals of the region. It is important to recognise that most of the sites used by grey seals in the southwest region currently have been used at least for many decades (Steven, 1935) and probably for very much longer. For example, as indicated in the references above, the use of sea caves is not an act of retiral by the seals in response to the enormous increase of use of the coastal zone through the twentieth and into the twenty-first centuries. It is something they have always chosen to do. Similarly, the use of the Longships haul-out site is very long-term. To date, any abandonment or near-abandonment of specific sites is likely to have resulted, primarily, from cliff falls that have rendered a site uninhabitable, by increasing use of the site by people or – in some but not all instances - by culling. In the nineteenth century on Lundy, there are anecdotes describing how sailors used to make irregular visits to Seal’s Hole on Lundy to club seals to death. This remains the best-known seal cave on Lundy and yet continues to be used, the year round, by seals. Download 1.63 Mb. Share with your friends:
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