The status of grey seals (Halichoerus grypus) at Lundy, 2008-2009
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4.4 Abundance and DistributionEfforts to visit the west coast seal sites during this survey period were frustrated on 9 of the 12 monthly visits to Lundy. Consequently, the degree to which they distort perception of numbers of seals using the island sites remains unknown. However, the three visits to these sites (Jenny’s Seal Hole and Aztec Seal Hole) suggested that they are used through the year. Furthermore, a count of 47 seals in Aztec Seal Hole on 19 April 2009 was the largest single count of seals using any site, in sea caves, on beaches or skerries, through the entire year. Both caves have storm beaches and tunnels off the main fairway, making it likely that seals would continue to use the caves when moderate of even heavy seas are running. This opinion was enhanced by the cries of seals emanating from these caves when they were inaccessible for survey work. The cries could be heard from the cliffs above. These caves also served as important seal nursery sites and the ones where the first pups were born in the 2008 season. Another west coast site, NW Seal Hole, was surveyed during 6 of the 12 visits and appears to be lightly used through the year, with never more than 3 adult seals present. The beach at Montagu’s Steps, near to the SW point of the island, was monitored on every visit because it is accessible from the land. It appeared to be used by seals only during the season of pup production, but this perception was influences by the heavy preponderance of SW or NW winds during survey work. Finally, seals were never observed ashore on Shutter’s Point Rock during survey work. However, records in the seal log, kept in the Marisco Tavern, indicate that it is used occasionally, when sea conditions are calm, possibly by relatively large assemblies of seals. The inaccessibility of the west coast sea cave sites would have remained so whether or not the research effort had been supported by a boat, because the weight of wave action on to their boulder beaches made safe landing impossible. However, it should additionally be recorded that the two most important west coast sea cave sites (described above) are located and orientated in such a way that, at low tide, they are subject to among the least violent wave action along the west coast. For the remainder of the island, the main haul-out sites, as well as the most regularly used, were Puffin Gully Cave, the skerries between NE Point and Gannet’s Rock, Gannet’s Bay, Mousehole and Trap, Inner Knoll, Three Quarter Wall Bay and Seal’s Hole. The highest count for the most easily surveyed area, the east coast – taken as a whole – was 99, made in October 2008. This coast was accessible for survey work on every visit to the island. The highest count made for the north coast as a whole was 82 in August 2009, although access to Puffin’s Gully Cave was impossible during 3 of the 12 months of the survey. The highest count made for the south coast as a whole was 14 in May 2009, although access to Seal’s Hole was impossible in 4 of the 12 months of the survey. The factors that determine the number of seals ashore (other than the number of seals present in the locality) are dominated by varying wind direction, wind speed and sea conditions. Essentially, once ashore it is evident that seals wish to avoid wave action, especially when first ashore and during the half-hour period when they may be settling and their pelages are drying. Overwhelmingly, seals used lee shore (and sea cave) sites whenever the wind reached Beaufort force 4 or above. Sea caves offered refuge in what appeared to be sub-optimal conditions because of the presence of storm beaches at the back of the caves. One main feature of verified seal abundance and distribution over the yearlong survey period was that seal numbers appeared to vary little through the year. This applies to the north, east and south coast sites, to which access was achieved through the year. The other main feature is that through the year, numbers of females always exceeded those of males, often considerably. DiscussionThe principal outcome of this survey is that it failed in its brief to report on the abundance and distribution of seals through the year, although the period of pup production and perception of the number of pups born is likely to be accurate. The failure was caused by sea conditions. For 9 of the 13 visits, moderate seas were breaking on to the west coast sea cave boulder beaches so that even with boat support, on the great majority of occasions, landfall could not be achieved. In seal survey work, there are ‘easy’ years, when conditions are benign, and ‘difficult’ years. 2008-2009 provided conditions that were at the most difficult end of the spectrum. Fresh southwesterly winds predominated throughout, with access to the west coast caves requiring northeasterly winds that rarely arrived. The conclusion has to be that any future survey work be Lundy-based, so that greatest advantage can be taken of ‘windows’ in periods of adverse weather (see 8. Recommendations: Management Plan below). Even then, there will inevitably be ‘holes’ in the data collection, because anecdotal reports said that sea conditions on the west coast had been continuously adverse since my previous visit. This means that the results are partial, as must be their analysis and discussion. This far, impressions have been achieved. 5.1 Pup production The use of sea caves rather than islands or remote, cliff-backed beaches for pup production at the onset of the season is similar to the pattern found in Cornwall, especially in the relatively nearby Boscastle locality (Westcott 2007) and in North Wales (Westcott 2002; Westcott & Stringell 2003). Similarly, nearly all remote beach sites are inaccessible from the land. No sea cave nursery site contained more than 5 unweaned pups. As elsewhere, e.g. Cornwall, North Wales, sea cave use is always relatively light compared with beach sites. This is likely to be because female seal behaviour at these sites can be aggressive and stressful, to the extent that other mothers and pups may abandon the site, swimming along the coast to another site. The same behaviour may occur in response to heavy sea conditions on to the cave site. However, during this survey, two of the three main sites (Halfway Wall Bay and Montagu’s Steps) were beach sites with small areas available to pups at high water. The two west coast sea cave sites, Aztec Seal Hole and Jenny’s Seal Hole, are also important nursery sites. The period during which they were used was comparable with that for island sites in the Isles of Scilly (Westcott & Rappel 2005). As elsewhere (for example Cornwall), the main season of pup production ran from late August to mid-October, with a tiny number of ‘early’ or ‘late’ pups being born – on this occasion - in December & January. An attempt to examine a second season of pup production found 28 pups born to 29 September 2008 compared with 23 in 2009. 5.2 Pup mortality As elsewhere in SW England, pup mortality prior to weaning was extremely low, apparently due to sites being largely protected against extreme wave action. Consequently, sites were safe enough to be used through the entire period of lactation, with low threat to the mother-pup bond. 5.3 Moulting As elsewhere, there were sometimes large assemblies of seals during the moulting period (December to April) using sea caves, especially Puffin’s Gully Cave, Seal’s Hole and Aztec Seal Hole (although only two visits were made to this site during that period. During the first visit, it was used almost exclusively by females. On the second visit, there was an atypical mixture of female and male seals, an event so unusual as to suggest this may, in fact, have been a post-moulting assembly, despite the presence of large quantities of seal hair on boulders above the high water mark. The moult period was similar to that described elsewhere (Cornwall, North Wales) but was atypical in that a mixed moulting assembly was found at one sea cave site (Aztec Seal Hole). Therefore, there may be unreliability in this sighting. Although large quantities of seal hair were present on the boulder beach, this may have been a post-moulting assembly. 5.4 Abundance & distribution This is the part of the report that is most flawed due to the inability to visit the west coast sites on sufficient occasions. However, it is evident from site visits as well as hearing seals calling from sea caves, that 4 sea caves are used the year round. On the west coast: Jenny’s Seal Hole and – apparently more used by the seals – Aztec Seal Hole. On the north coast: Puffin Gully Cave and on the south coast: Seal’s Hole. When the (predominant) wind is blowing from the SW, the main seal haul out sites through the year are found between Knoll Pins and the NE Point, with the major assemblies occurring usually in Gannet’s Bay and points just to the north and south of the bay. Less commonly, seals assemble in largest numbers on rocks at the north end in the vicinity of Puffin Gully Cave. Least commonly, Aztec Seal Hole was confirmed as the main west coast site. In effect, all observations confirmed that seals seek lee shores when the wind blows at force 4 or more – to the point when there is surf action on to sites where they are resting. This is precisely in accord with all observations made during North Wales and SW England seal surveys mentioned above. 6. Acknowledgements I am most grateful to Roger Fursdon for his illuminating insights regarding Lundy at sea level, for his occasional companionship and most especially the information he gave me regarding the use seals make of Virgin Springs Seal Hole. I am grateful for the hospitality offered by the warden, Nicola Saunders and her team, for the use of the caravan through the year and for boat support on my first and last visits. 7. References Baillie, C.C. and Clark, N.A. 1974. Brief visits to the sea-level caves on the east side of Lundy. Annual Report of the Lundy Field Society, 25, pp.59-62. Bonner, W.N. 1989. The Natural History of Seals. Christopher Helm. 196pp. Caudron, A.K., Joiris, C.R. and Ruwet, J.C. 2001. Budget d’activité comparitif dans les colonies de reproduction du phoque gris Halichoerus grypus. Importances des populations marginales. Mammalia, Tome 65, 3, pp.373-382. Chanter, J.R. 1877. Lundy Island. 248pp. Langmans, Green and Co., London. Chilvers, R., Colebourne, M., Grant, B., Oliver, R. and Lea, S. 1999. Vigilance in Grey Seals as a Function of Time Since Haul Out. Annual Report of the Lundy Field Society, 50, pp.41-48. Clark, N.A. and Baillie, C.C. 1973. Observations on the Grey Seal (Halichoerus grypus) populations of Lundy. Annual Report of the Lundy Field Society, 24, pp.41-42. Clark, N.A. 1977. The composition and behaviour of the grey seal colony of Lundy. Annual Report of the Lundy Field Society, 28, pp.32-38. Duck, C. 1995b. Seals pp.146-148, in: Coasts and Seas of the United Kingdom (Coastal Directory Series). Region 11 The Western Approaches: Falmouth Bay to Kenfig. Eds. Barne et al., Joint Nature Conservation Committee, Peterborough. Download 1.63 Mb. Share with your friends:
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