The status of grey seals (Halichoerus grypus) at Lundy, 2008-2009
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- 4.2 Pup mortality
- Date of birth
4.1 Pup ProductionIn both the full 2008-2009 season, and for the first four weeks of the 2009-2010 season, white-coated grey seal pups were found on remote beaches and on sea cave beaches. Dead pups were found in sea cave entrance waters and in the shallows off a boulder beach. The earliest known births occurred at the end of August: two were estimated to have been born on 30 August 2008. The last births occurred in late January: estimated to have been the 23 and 25 January 2009. The earlier births were predominantly at sea cave sites. Only later were pups born at remote boulder beach sites backed by cliffs. It is likely that a small proportion of such pups had been born at sea cave sites and had swum to open beach sites due to environmental conditions (wave action on to nursery beaches) or to conflict and aggression between seal mothers (some seal mothers aggressively deny passage around them by other mothers attempting to reach pups deeper inside the cave). This may have been especially true for the beginning of the 2009-2010, when sea conditions were generally more disturbed than during the previous season. In 2008-2009: 23 pups were born on sea cave beaches. 15 pups were born on remote, boulder beaches. 17 of the first 23 pups to be located were born on sea cave beaches. It appears that the early births occur predominantly in sea caves. Of the 38 births recorded, 27 took place in September. 2 took place in August, 3 in October, 2 in November, 2 in December and 2 in January. Of the 38 births recorded, 3 definitely died prior to weaning. Of the remaining 35 seals, 18 were seen weaned and moulted. The remainder were not seen as weaned individuals, due to the monthly timing of the visits and problems of site access due to adverse sea conditions. The main nursery site was Halfway Bay Beach, a wide boulder beach with tiny coves remaining uncovered at high water, just south of Tibbett’s Point. In December, one sea cave, previously undiscovered during this survey, was identified at the north end of the Island. In discussions with Roger Fursdon, engineer for the Island, it became clear that the site – Virgin Springs Seal Hole – may be one of the most important nursery sites on Lundy. Therefore, the pup production estimate for Lundy (and for the sea cave sites) is likely to be underestimated by at least 5 pups. The date when pup production began could also be earlier than this study identified, although a site visit on 24 August 2009 found that pup production had not yet begun. In 2009-2010: 15 pups were born on sea cave beaches. 8 pups were born on remote, boulder beaches. 15 of the first 23 pups to be located were born on sea cave beaches, supporting the notion formed in the previous season that the early births occur predominantly in sea caves. Of the 23 births recorded, all took place in September. Of the 23 births recorded, only one definitely died prior to weaning. Of the remaining 22 seals, only 3 were seen weaned and moulted. The remainder were not seen as weaned individuals, mainly because of the slightly later onset in pup production in the 2009-2010 season. The main nursery sites to this point in the season of pup production were Jenny’s Seal Hole (a west coast sea cave with a substrate of large boulders and three tunnels leading off the main fairway) and Montagu’s Steps, here classified as a remote beach but actually a complex of small caves, a cleft and boulder beaches, sheltered behind Goat Island near the SW tip of the island . 4.2 Pup mortalityOf the 38 pups produced at Lundy in the 2008-2009 season of pup production, two died very early, being abandoned or stillborn. A third pup was abandoned during lactation, at Montagu’s Steps. This compares with only one known mortality in the season commencing September 2009. There was no evidence of any other pup dying prior to weaning. Table 1: Lundy sites where pups were born, August 2008 – June 2009
Table 2: Lundy sea cave sites where pups were born, August 2008 – June 2009.
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