Grey seal (female)

© S. Heinrich, SMRU

The UK has two species of seal: about 36% of the world’s population of grey seals live here as well as about 4% of the world’s population of harbour (or common) seals. Although both species can be seen all round the UK coast, they are considerably more abundant in some areas than others. Some 90% of grey seals and 80% of harbour seals live in Scotland. Grey seal pup production has been monitored since the early 1960s; harbour seals have been monitored since the late 1980s. Both grey and harbour seals are probably more numerous now than in the recent past, when they were locally hunted.

Under the Conservation of Seals Act 1970, the Natural Environment Research Council has a statutory obligation to provide the UK government with ‘…scientific advice on matters related to the management of seal populations’. A major component of the advice required is up-to-date information on the size and distribution of UK seal populations. Although grey and harbour seals are not protected species (apart from in Northern Ireland), some protection comes from the Conservation of Seals Act 1970 and the EU Habitats Directive. The Scottish Government will extend seal protection measures under the Marine (Scotland) Act 2010. Five species of Arctic seal occasionally visit the UK coast.

Grey seals

The UK has around 182 000 grey seals. Grey seal populations are estimated on the basis of pup production, which is monitored annually at colonies that contribute some 85% of pups born in the UK. Most colonies are surveyed using aerial photography, others through ground counting. The great majority of colonies in Wales and south-western England are extremely difficult to survey because grey seals breed in caves or on beaches at the foot of remote cliffs. Figure 3.3 shows the breeding colonies. After decades of increase, following the end of culling in the 1970s, total grey seal pup production appears to be levelling off in the UK and is now rising at only a small number of colonies. At least part of the previous increase in grey seal pup production is due to the increased availability of breeding sites following the abandonment of human settlements on remote islands, including through automation of lighthouses. The current reduction in the rate of increase is probably because of density dependent factors affecting the population as a whole. It is not yet clear whether factors affecting survival are more important than factors affecting fecundity.

Figure 3.3 The location of grey seal breeding colonies in Great Britain and Northern Ireland. Text labels identify the Special Areas of Conservation (SACs) where grey seals are one of the main reasons for the creation of the protected site. Site names in brackets are SACs where grey seals have only contributed to the reasons for designation and are not the main reason for the creation of a SAC.

Harbour seals

Harbour (or common) seal

© A. Coram, SMRU

Harbour seals do not aggregate when breeding and mothers with young pups are highly mobile. However, they are less dispersed during their August annual moult, which is when aerial surveys take place. In south-eastern England and parts of Scotland surveys are annual; in the rest of Scotland harbour seals are monitored at four to five year intervals due to the large area involved and the cost of undertaking the monitoring. In specific parts of Northern Ireland, counts are monthly.

Harbour seal numbers have declined significantly in Shetland, Orkney and the on east coast of Scotland, by more than 50% since 2001. There has been a smaller decline in the Outer Hebrides but numbers on the west coast of Scotland have remained relatively stable. The causes of these localised declines are not yet known.

Contributing factors could be either natural or anthropogenic or both and could include: competition with grey seals, predation by killer whales (in the Northern Isles), and declines in important prey species (such as sandeels) and unregulated shooting (in some local areas). As a charismatic species, harbour seals are often highly valued (e.g. to the local tourist industry). Thus, even when populations are very small such as in southern England, pressure on these individuals is considered significant. Figure 3.4 shows the distribution of harbour seals.

Two outbreaks of phocine distemper virus (PDV) seriously affected the harbour seal population in eastern England with 50% dying in 1988 and 22% dying in 2002. In Scotland, an estimated 5% died in 1988 and far fewer in 2002. In marked contrast to populations elsewhere in Europe which showed an immediate and rapid recovery, harbour seals in eastern England took three years to recover from the 1988 outbreak and have yet to begin recovery following the 2002 outbreak. PDV outbreaks are likely to recur in the future but it is not possible to predict the proportion of the population that might be affected, which populations are most vulnerable (besides eastern England) or precisely when outbreaks will occur. It is even harder to predict the future susceptibility to PDV of harbour seal populations in northern and eastern Scotland, given recent declines and the lack of any obvious cause. The limited impact of PDV on harbour seals in Scotland and Northern Ireland in 2002 may result in reduced population immunity and increased susceptibility to a future outbreak. The Scottish Government and Scottish Natural Heritage have funded a number of projects investigating the declines in harbour seals in northern and eastern Scotland. Increasing renewable energy production, which may impact on marine mammal populations, may require more up-to-date and detailed information on seal distribution in relevant areas. Harbour seal monitoring frequency in Scotland is infrequent compared with grey seal monitoring.

Figure 3.4 The distribution and number of harbour seals in Great Britain and Northern Ireland in August, by 10 km squares, from surveys carried out between 2000 and 2006. Text labels identify the Special Areas of Conservation (SACs) where harbour seals are one of the main reasons for the creation of the protected site. Site names in brackets are SACs where harbour seals have only contributed to the reasons for designation and are not the main reason for the creation of a SAC.