The sensitivity of grey & common seals

In general, it is the habitats for grey and common seals in which they are found that are to be protected under the Habitats Directive. The sensitivity of these habitats has been addressed in the previous sections. However, it is important that consideration is also given to the sensitivity of the species themselves to human activities. This may be as important an influence on current stocks and breeding patterns of seals as the protection of their habitats.

Common seal, phoca vitulina: The UK holds some 28,000 common seals, approximately 50% of the EC population. The species is found from Strangford Lough in Northern Ireland, through the south shores of the Clyde and clockwise round the coast to the Thames Estuary. Site selection has favoured sites that are suitable both as haul-out sites and also for pupping.

Grey seal, halichoerus grypus: The UK holds some 115,000 grey seals, approximately 50% of the world population and 95% of the EU population. There are breeding colonies all around the UK coast, from the Scilly Isles clockwise to the North Norfolk coasts. The colonies vary greatly in size. The largest breeding colonies have been selected for designation, based on pup productions. Colonies have also been selected to ensure coverage of the geographical range of breeding in the UK.

Rejinders (1981), suggests that UK populations of the grey and common seal each represent 40% of the world totals. Such figures highlight the international conservation importance of these populations.

Tourism based on wildlife watching, including grey and common seals, is a growing business which may often promote conservation interests. For seals, most of the activities take place on land as they are difficult to observe and track at sea. In particular, their presence in shallow coastal waters or at haul-out sites is a major attraction for wildlife watchers. Within these breeding and pupping sites, the seals are visible and, in some instances, actually accessible to the public from either land or boat.

For the purposes of this report, a distinction is made between those haul-out sites which are for breeding, pupping or resting as at each of these sites the sensitivity of the species differs.

There is a large body of information available about the land-side behaviour of seal species, including breeding conditions, pupping sensitivity and resting haul-outs. Brown and Prior (1997) suggest that the main on-land indicators of disturbance to seals are:

• interruption and disturbance of rest, resulting in lower fitness and health
• interference with nursing young, reducing their health
• separation of mother and pup, resulting in starvation and death of pups
• abandonment of haul-out sites

Observations have shown that when seals perceive a threat, they tend to race from their haul-out sites and enter the water. The length of retreats to water may be a good indication of the level of threat as perceived by the seal. However any flight response by the seals can be taken as evidence of disturbance. To quantify the reaction of hauled-out seals to human presence, Mortenson (1996) devised a scoring system to identify the intensity of the seals reaction. The definitions within this system are as follows:

Level 1 - alerting: head orientation of the seal towards the direction of any source of disturbance

Level 2 - movement: any movement of one or more seals from their resting position away in any direction from the disturbance source or towards the waters edge

Level 3 - ‘flushing: one or more seals moving from haul-out sites into the water

Such a system is an easy and effective way of monitoring the effects and frequency of human disturbance at site level. The key impacts of such disturbance are on seal fitness and health and, in severe cases, possible mortality.

Disturbance issues are not the only potential threats to Grey and Common seals in the mSAC areas. These species are also sensitive to actively fished nets, debris, pollution and effects on the food web. Site managers and relevant authorities should give consideration to these potential threats when assessing recreation at site level.

The resilience of the seal population on the Wash has been closely monitored over the last decade following an outbreak of a serious virus in 1988 which was reported to have killed 50% of the population. Ten years later, new counts have revealed that the population is now approaching 1987 levels, before the outbreak of the virus. This recovery suggests that the seal population in the Wash area is remarkably resilient, even to potentially catastrophic events. The issue of disturbance to seals is dealt with a separate section.

The tables below summarise the potential threats to grey and common seals from land and waterborne processes.

Water based processes

Land based processes

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