Abstract
Harbour seal (Phoca vitulina) numbers along the coast of Iceland were monitored by aerial survey in the period 1980-2006. Trends in the abundance of the harbour seal population on the whole coast and in coastal regions of Iceland waters were estimated using ANCOVA on the survey counts, corrected for the influence of several covariates. Harbour seals were found in every coastal area, but were most abundant in Faxaflói, Breiðafjörður and on the northwest coast inthe beginning of this study. Harbour seal numbers declined significantly at a rate of rest = -0.04 (SE 0.005) yr-1 during this period. Decline was highest in Faxaflói and at the south coast (≅7%), while the east coast experienced a significant but lesser (≅1%) decline. Other coastal areas did not show significant trends. The northwest coast was the richest harbour seal area in Iceland in 2006. In Icelandic waters seals are commercially harvested, and unreported but probably high numbers of harbour seals are killed intentionally by shooting and accidentally in fishing geareach year. These factors likely contributed to the overall observed decline in seal numbers.
Highlights
An understanding of population status of the Icelandic harbour seal (Phoca vitulina vitulina) is a fundamental requisite for its effective management and conservation
Aerial surveys Beginning in 1980 the whole coast of Iceland, except the island Grimsey far off the north coast (Fig. 1), and the island of Hvalbakur far off the southeast coast was usually surveyed in the period late July- early September
Counts from site no. 3 in survey year 1980 and site no. 63 in survey year 1992 (Fig. 1), had large leverage and were probably outliers. These sites had zero counts in these years, but some or numerous harbour seals were observed there in the other survey years. These two counts were not excluded from the analyses and probably did not influence the overall results much, these zero counts could have caused the no significant trends observed at the sites no. 3 and 63 (Fig. 1 and Appendix 1)
Summary
An understanding of population status of the Icelandic harbour seal (Phoca vitulina vitulina) is a fundamental requisite for its effective management and conservation. The exploitation of the stock and the unreported but possibly high numbers of harbour seals killed intentionally by shooting and accidentally in fishing gear each year (Hauksson and Einarsson 2010) makes it highly relevant to monitor harbour seal abundance on a regular basis. Current and accurate information on trends in abundance is needed to understand the role of the population in ecosystem dynamics, its potential interactions with fisheries, the impacts of global climate change, and other anthropogenic changes caused in habitat (Small et al 2003). Arnþór Garðarsson (unpublished) counted harbour seals from an aircraft on part of the Icelandic coast in the summers of 1973 and 1977. He found 2,500; 632 and 3,568 harbour seals in Faxaflói, Vestfjörðum and the northwest - north-
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