Local declines in the abundance of harbour seals: Implications for the designation and monitoring of protected areas

Abstract

1. Information on the abundance of European pinnipeds is required to assess interactions with fisheries and to meet new conservation obligations under the European Community (EC) Habitats Directive. A detailed time-series of data has documented increases in grey seal populations, but there remains considerable uncertainty over the current status of UK harbour seal populations. 2. We present data on changes in the abundance of harbour seals in a study area within Orkney, Scotland, UK, previously considered a stronghold for this species. In 1998, intensive shore-based counts of both adults and pups were only 16-36% of similar counts made between 1984 and 1987. Furthermore, a significant reduction in the proportion of yearlings present in haul-out groups indicated a reduction in local recruitment. 3. Current monitoring of UK harbour seals, using wider-scale aerial survey techniques, has provided important estimates of site distribution and relative abundance at regional and national scales. However, these larger-scale surveys lack associated data on within-year variation in counts at particular sites. Consequently, they cannot currently be used to explore the spatial scale of the changes in seal numbers that we report here. Similarly, current data from wider-scale monitoring cannot be used to determine whether observed local changes in abundance result from redistribution or a change in survival or reproduction. 4. Management and monitoring plans are currently being developed for special areas of conservation (SAC) for harbour seals in response to the EC Habitats Directive. We suggest that more intensive research is required to assess whether or not similar changes in the abundance and age structure of seals have occurred in these areas. Without a better understanding of the current status of harbour seals both within and outside proposed SAC, future efforts to monitor the effectiveness of management initiatives will be constrained.