. The Canadian field-naturalist. 326 The Canadian Field-Naturalist Vol. 102 100 50-. N ' D J F ' M A 1963 1964 Figure 5. Maximum number of Steller Sea Lions seen each month on Mclnnes Island by hghthouse keepers during 1963 to 1964. remain in the area, although were not always hauled out at the year-round site. In this regard, the mean number hauled out per month is not a particularly good indicator of the number of sea hons using the site. Frequent temporary depar- tures can severely bias the mean number as an indicator of site importance. The maximum number seen per month is a more useful st
. The Canadian field-naturalist. 326 The Canadian Field-Naturalist Vol. 102 100 50-. N ' D J F ' M A 1963 1964 Figure 5. Maximum number of Steller Sea Lions seen each month on Mclnnes Island by hghthouse keepers during 1963 to 1964. remain in the area, although were not always hauled out at the year-round site. In this regard, the mean number hauled out per month is not a particularly good indicator of the number of sea hons using the site. Frequent temporary depar- tures can severely bias the mean number as an indicator of site importance. The maximum number seen per month is a more useful statistic. Figure 6 illustrates this point for an exposed winter haulout. The total number seen at all year-round sites in summer remained relatively stable between 1957 and 1982, averaging about 1 900 animals (Table 6). That the number of sea lions did not decrease during this time, as found on rookeries, is surprising. The reason may be that the numbers seen on year-round haulouts are not a simple proportion of the numbers on rookeries. An example in which little correlation existed between an increase in numbers on a rookery and the increase in numbers on a nearby year-round haulout was Forrester Island and Joseph Rocks. Joseph Rocks is a large year-round haulout that can physically accommodate many more individu- als than it does currently. A 75-fold increase in the number of animals took place on the rookeries of Forrester Island between the 1930s and 1973 to 1982 (Table 3). Yet, only a two-fold increase was seen on Joseph Rocks during the same period (Bigg 1984). Perhaps local food supply limited the number of sea lions that could be supported at a year-round haulout. Emigration could have taken place. Another possibility was that the numbers seen during the 1950s were biased due to harassment prior to censuses. Also, the number of animals on year-round haulouts could have been reduced for sea lions born on rookeries in British Columbia, but their reduction was masked by an
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