Science Advisory Report  2009/011

Population Assessment Pacific Harbour Seal (Phoca vitulina richardsi)

Summary

• DFO began conducting aerial surveys in British Columbia in the early 1970s to determine harbour seal abundance and distribution, and monitor population trends. Surveys are flown in small aircraft at low tide toward the end of the pupping season, when maximum numbers of animals are hauled-out and can be counted. Correction factors are applied to account for swimming animals missed during surveys.
• Surveys in the Strait of Georgia and Index Areas in other parts of the province indicate seal populations grew exponentially at a rate of about 11.5% per year during the 1970s and 1980s, which probably represents the biological maximum rate of increase for this species. The rate of increase began to slow in the mid-1990s, and abundance now appears to have stabilized.
• The recent population increases are thought to represent the recovery of population that had been depleted by over-hunting prior to the species being protected in 1970. Approximately half a million harbour seals are estimated to have been killed on the west coast of Canada for pelts or bounty since the late 1870s.Large commercial harvests taken during 1879-1914 and 1962-68 are thought to have depleted populations.
• Seals are widespread and do not congregate to breed, so the entire coastline must be searched to census populations. To date, about 82% of British Columbia’s 27,200 kilometer coastline has been surveyed, and nearly 1,400 haulout sites have been identified. The highest densities of harbour seals occur in the protected waters of the Strait of Georgia (13.1 seals per km shoreline), which represents only 11% of the coastline but supports 37% of the seal population. In areas that have been surveyed outside the Strait of Georgia, densities average about 2.6 seals per km of shoreline, and this average has been applied to unsurveyed coastline to estimate total abundance.
• It is estimated that about 105,000 harbour seals currently inhabit coastal waters of British Columbia, compared with a population that had been reduced to perhaps 10,000 when the first surveys were conduced in the early 1970s.
• The B.C. population represents about 29% of the total of 360,000 harbour seals estimated to inhabit the NE Pacific Ocean. Recovery of harbour seal populations has also occurred in California, Oregon, Washington and parts of SE Alaska, renewing concerns over their impact on fishery resources and interest in their role in marine ecosystems.

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