Sunday, 26 March 2017

Grey Seals at Donna Nook

24th March 2017

This month's lecture meeting brought us a talk by Rob Lidstone-Scott, Lincolnshire Wildlife Trust's Outer Humber warden about his work with the grey seals, Halichoerus grypus, of Donna Nook National Nature Reserve.

Rob explained how his job was more of a people warden than a seal warden, the seals being a law unto the themselves while the people who come to look at them, around 70000 each pupping season, need to be cared for. Managing the visitors, car parking, ensuring minimum disturbance of the seals and safety of the public, is a formidable task.

We learnt something of the seal's biology and life-cycle and how the North Sea populations have shifted and grown in recent years, with large increases at the southern rookeries of  Donna Nook, Blakeney and Horsey, while the Farne Isle population has stayed more constant. The Scottish populations of the Hebrides and Northern Isles are still much larger.

Satellite tracking of Donna Nook seals show that the Lincolnshire seals range along the coastal waters of Lincolnshire and Yorkshire and the shallow waters of the Norfolk Banks and Dogger Bank, feeding mostly on bottom dwelling fish such as dragonet, short-spined sea-scorpion and sand-eel, cod and flat-fish.

Rob recounted the events surrounding the tidal surge of 5/6th December 2013 when the waters over-topped the chestnut paling fence, washing seal pups and adults into the dunes. Rob and his fellow-wardens had to cut the fencing and do their best to ensure the safety of the pups, the great majority of which survived and were reunited with their mothers.

It is noteworthy that the pup mortality rate, at under 10%, on these southern sandy beach rookeries is much lower than on the rocky sites such as the Farne Islands, where mortality may be 40%. With a female living about 30 years and producing a pup most years there is scope for a steady but large increase in population. Orcas are very rare in the North Sea so the seals are the top predator. Limiting factors on numbers may be disease, pollution (this may be a significant cause of mortality in the Baltic population) and entanglement with fishing gear. Seal culling is a vexed issue, no longer affecting the Lincolnshire and Norfolk populations, but significant in northern, Scandinavian and Canadian populations.

Further reading:

The Wildlife Trusts

LWT Donna Nook

Joint Nature Conservation Committee

Seal Conservation Society

National Trust Blakeney

Friends of Horsey Seals

Berwickshire and Northumberland coast

Scottish Natural Heritage

Hebridean Whale and Dolphin Trust

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