For the Steller sea lion, the vast majority of births occur at traditional rookeries, and because pups are confined to land for the first month of life, surveys of rookeries at the end of the pupping season provide a nearly complete estimate of annual pup production.
This disadvantage is especially pronounced for counts made at oblique angles from aircraft circling rookeries or from vessels adjacent to the sites.
Few reliable counts of pups were available before the 1970s, but counts of non-pups on rookeries have dated back to the early 1990s.
Counts from the 2002 populationwide survey (Table 1) indicated a fairly tight relationship between the number of pups and nonpups counted on rookeries (Fig.
In southeastern Alaska, the Alaska Department of Fish and Game periodically conducted ground counts of pups on rookeries from 1979 through 1998, and used vertical 126-mm format photography to count pups since 1998.
In most cases the counts were made by professional biologists or naturalists hired by government agencies to conduct sea lion investigations, and special trips were made to rookeries to obtain first-hand counts; therefore it is unlikely numbers were grossly inaccurate.
Our null hypothesis was that there was no difference in pup growth rates among rookeries in southeast Alaska, the Gulf of Alaska, and the Aleutian Islands.
Rookeries in the Gulf of Alaska and the Aleutian Islands are in the area of declining population, although the rookery on Fish Island has not shown as precipitous a decline.
Choosing only pups with fresh umbilical cords minimized the age bias (Trites, 1993) that occurs when pups are captured at different times and rookeries (Table 1).
Similar protocols were used at all rookeries, except Marmot Island in 1990 and 1991, when only BM and SL were measured, and the age of pups was not estimated.
TBL was then compared between male and female pups and among rookeries.
When all pups at all rookeries were combined (n=116), %TBW was 72.