Habits
In Kent grey seals are transitory, spending long periods of time at sea, often travelling hundreds of kilometres during foraging trips that can average two to three days. Grey seals are regularly seen on intertidal sand bars in the English Channel, southern North Sea and Thames Estuary where they haul-out during the ebbing tide but remain close to their fishing grounds. Few grey seals are recorded in Kentish riverine habitats, but anecdotal reports have recorded them travelling several miles upstream into the Great Stour, river Medway and river Thames. Their diet consists of sand eels, gadoid fish such as cod, pollock, haddock and whiting, as well as flatfish.
Reproduction and life cycle
Grey seals have a protracted breeding season. Pupping occurs on ‘rookeries’, sites where females aggregate and give birth between late September and December. Pups are born with lanugo (woolly down fur), which helps protect them against the elements as they develop on land at the rookeries. Pups are weaned after 18 to 21 days and lose their natal lanugo; their mothers will then abandon them. Female grey seals come into oestrus as the pups are weaning and are often shepherded by large bull seals awaiting the opportunity to mate. Copulation lasts for about 20 minutes and females may be mated up to three times, not necessarily by the same male. Upon successful mating the fertilised egg is subject to delayed implantation like that of common seals. The egg finally implants three to four months later at the same time as the female completes her annual moult.
No breeding sites have been recorded around the Kent coast, although pups with their natal lanugo have been found on less disturbed beaches in east Kent.
Male grey seals reach sexual maturity at six years of age but may not hold a breeding position within the group until they reach 10 years, whereas females show signs of sexual maturity at only three to five years old. Males will live on average for 25 years, whereas females may live for up to 35 years.
Distribution, status and conservation
Grey seals are recorded on the majority of the county’s intertidal sand bars including those of the Margate sands complex, West Barrow, North Knob and Knock John, Shingles and Shingles Patch, Pan Sand and Ridge. The largest aggregation of grey seals can be found on the Goodwin Sands complex, which is approximately six miles off the Deal coast in Kent.
The number of grey seals recorded in Kent continues to increase each year. Recent studies carried out by the Zoological Society of London suggest that there are about 200 grey seals in the Thames estuary alone. When coupled with larger colonies on the Goodwin Sands in the English Channel, the population may reach a total close to 600 seals. Whilst these figures are conservative estimates at best, they do reflect earlier reports by local tour operators, light aircraft users and fishermen whose accounts confirm similar numbers seen during their working lives in these areas.
Recent surveys at the Thames Estuary in 2024 counted 714 grey seals, from this an estimate of a ~2,988 strong population.
