To ask the Scottish Executive what its estimate is for the grey and common seal population (a) over each of the last 30 years and (b) each of the next 30 years.
The estimates of grey seal populations in Scottish waters from 1984-98 shown in the table below are based on annual surveys of breeding colonies in the Outer Hebrides, Inner Hebrides, Orkney, the Isle of May and two English sites. The Scottish population figures have been arrived at by deducting the proportion of the population related to the two English sites. They are a consistent series calculated from a model that derives estimates of pup production from aerial survey counts and a model that estimates the size of the population required to produce these pups. An estimated additional 8,900 animals are associated with breeding sites that are not surveyed annually.
Pup surveys prior to 1984 did not include the Inner Hebrides. For these years, in the table below, the population estimates given are the product of the pup production estimate for the surveyed areas and the mean ratio of total population to pup production for these same areas from 1984 to 1998.
Year | Estimated Scottish Population to the Nearest 500 animals (aged 1 year and over) | | Year | Estimated Scottish population to the Nearest 500 animals (aged 1 year and over) |
1970 | 29,000 | | 1986 | 47,500 |
1971-1973 | No Surveys | | 1987 | 50,500 |
1974 | 32,000 | | 1988 | 54,500 |
1975 | 34,000 | | 1989 | 58,000 |
1976 | 35,500 | | 1990 | 61,500 |
1977 | No Survey | | 1991 | 65,000 |
1978 | 33,500 | | 1992 | 69,000 |
1979 | 36,500 | | 1993 | 73,500 |
1980 | 42,500 | | 1994 | 78,500 |
1981 | 44,000 | | 1995 | 83,500 |
1982 | 44,000 | | 1996 | 89,500 |
1983 | No Survey | | 1997 | 95,000 |
1984 | 41,500 | | 1998 | 101,500 |
1985 | 44,500 | | | |
Predictions about future population size are very difficult to make and are dependent on a number of assumptions. Two alternative predictions for grey seal numbers over the next five years are contained in the report Scientific Advice on Matters Related to the Management of Seal Populations: 1999, a copy of which is held in SPICe. Because of uncertainty about future changes in pup production, it is not meaningful to predict population size any further into the future than this.
Surveys of common seals between 1974 and 1980 were carried out from boats during the breeding season (June/July). Surveys since 1988 were by helicopter using a thermal imaging camera and were carried out during the August moult when the greatest and most consistent numbers of seals are thought to haul out. The numbers in the table below are counts of seals hauled out on land and represent minimum estimates of the population. A significant proportion of common seals will be at sea even during this period and it is therefore much more difficult to be precise about the total population based on these minimum figures.
Year |
1974-1980 (Boat survey) | 1988-1994 (Helicopter) | 1996-1997 (Helicopter) |
Adults Pups | Adults | Adults |
9,328 1,495 | 26,667 | 29,600 |
The increases between boat and helicopter survey results are partly due to the extension of the area surveyed by helicopter (successive surveys have covered larger areas), partly due to the change in methodology (up to twice as many seals may be detected when surveying by helicopter compared with boats), partly due to the different timing of surveys (seals spend more time hauled out during the August moult than during the June/July breeding season), and presumably also partly as a result of the cessation of harvesting, particularly in Shetland and Orkney. At present, we cannot say how the trend in numbers counted at haul-out sites relates to trends in population size.
The total Scottish population cannot be estimated accurately but is currently thought to be between 43,000-52,000 animals. There is insufficient information to allow future predictions of numbers of common seals to be made.