Steller Sea Lion Recovery Investigations in Alaska , 1992 - 1994 Contributors

The United States population of Steller sea lions (SSL), Eumetopias jubatus, is classified as ''threatened'' under the Endangered Species Act" because of a recent 73% decline in numbers. National Marine Fisheries Service (NMFS) has recommended that the US population of SSL be divided into two stocks, with an east-west division at 144 west longitude, based largely on genetic evidence. Since 1992, the Alaska Department of Fish & Game (ADF&G) and NMFS have been the recipients of congressional appropriations to study the decline and develop management strategies for population recovery. The basis for much of the research has been an "experimental/control" approach comparing population characteristics between the depressed westem stock and the increasing Southeast Alaska (SEA) portion of the eastern stock. Research then could focus on those factors that are different between stocks to determine their role in the decline and eventually to develop appropriate strategies to enhance population recovery. In addition to ADF&G and NMFS several other scientific groups (cooperators), with specialized expertise, have joined the research effort. In this report we present findings from our research and that of our cooperators. Counts of SSL pups and nonpups were made at rookery and haulout sites in SEA between 1979 and 1995. Historical data on SSL abundance from earlier in the century were also examined. Counts of both pups and nonpups showed a positive trend (pups =+6.86%/yr, nonpups =+4.83%). The lower rate of increase for nonpups was probably due to the reduced presence of subadults from the depressed western stock. During this period two sites, White Sisters and Hazy Island, developed into significant rookeries. We estimate, based on total counts of pups, that in 1994 the SEA breeding population numbered approximately 17,000 animals. We conclude that SSL are abundant in SEA and are probably at the highest level of this century. These findings question the logic behind classification of the SEA subpopulation as threatened. Comparisons of composition data from Sugarloaf Island rookery, in the area of decline, and Forrester Island rookery, in an increasing population, showed no differences that indicated reduced juvenile survival. There was an increasing trend in the proportion of adult males at Sugarloaf and a decreasing trend at Forrester. The mean ratio of subadult males was higher for Sugarloaf than for Forrester. Ratios of pups to adult females differed among years at both locations which indicates that annual variations in the environments affect productivity. We found that pupping dates for SSL at Sugarloaf Island, in the .depressed western stock, were about 10 days later than at Forrester Island, in the increasing SEA portion of the eastem stock. Pupping dates also differed between years at Sugarloaf and Forrester. At Sugarloaf Island pupping appeared earlier in 1995 than during 1980. At Forrester, between 1992 and 1995, there was a trend towards later pupping. It had previously been thought that the timing of pupping was synchronous throughout the species range. There are reports in the literature for other pinnipeds that timing of pupping is affected by nutritional status. We suggest that these findings support the hypothesis of undernutrition as a factor in the decline of the western stock but do not discount the presence of a genetic component to birthing dates. Late pupping is likely a symptom of undernutrition rather than a major mechanism behind the decline. A potential mechanism in aiding the recovery of the western stock of SSL is emigration of animals from the SEA. It is known 'from other studies that SSL are highly mobile with movements of many hundred and even thousands of kilometers. However, current information indicate adult females show a high degree of fidelity to their site of birth or to nearby areas. We marked 813 pups at the Forrester Island rookery in the increasing SEA portion of the eastern stock during 1994 and 1995. Resightings of the marked animals have been made at sites ranging from Seattle, Washington to Kodiak, Alaska. Between 1998 and 2002 searches for these marked animals will be made on rookeries from Oregon to the Aleutian Islands to determine the rate of emigration. Survivorship rates will be estimated using the resightings of marked animals. One hypothesis proposed to explain the decline is that juvenile SSL are nutritionally stressed and are experiencing high mortality during winter. It is postulated that activity budgets of juvenile SSL should reflect nutritional status. A comparative behavioural study of juvenile activity budgets was conducted at haulout sites in both the declining western stock (Cape S1. Elias) and in the increasing SEA portion of the eastern stock (Timbered Island). Activity data are currently being analyzed and will be reported in a MS thesis from the University of British Columbia. The target date for completion is October 1996. A comparative study of reproductive behaviours of SSL was conducted at the Sugarloaf Island rookery in the declining western stock and at Forrester Island in SEA, an increasing segment of the eastern stock. During an EI Nino event, which resulted in drastic food shortages ranging from Chile to California, a number of reproductive behaviours were noted to change in otariids. Based on findings of field research with otariids and experimental studies of terrestrial mammals, data on the following behavioural, developmental and physica.l indices were collected at the two sites. These included activity budgets, maternal attendance patterns, male tenure duration and territory size, copulation frequency and time, delayed weaning, ea.rly pup development and maternal care postpartum, and the occurrence of fungal patches. Preliminary results indicate that females spend more time nursing their pups, are more aggressive and have a longer perinatal period in the area of decline. Trip durations appear to be shorter in the area of decline. The final results of this study will be reported in a MS thesis from the University of British Columbia. The target date for completion is December 1996. . Indices of adult female reproductive effort, female body condition, and pup growth were studied for Alaskan Steller sea lions. Data from declining populations at Chirikof Island in 1993 (C93), Marmot Island in 1994 (M94), and Fish Island in 1995 (F95) were compared to a stable population at Lowrie Island in 1993 and 1994 (L93, L94). Trip duration of adult females was monitored by deploying VHF transmitters. Female body condition and known-age pup growth, body condition and milk intake were measured during their first 40 days postpartum. There was a significant difference among locations in mean trip duration, the longest at L94 (29.1 hrs) and shortest at C93 (11.2 hrs). There was no significant difference among locations in pup mass at age 0-5 days (mean = 21.0 kg), although males (22.4 kg) were significantly heavier than females (19.5 kg). There was a significant difference among growth rates, with the C93 and F95 pups growing faster in their first 40 days than the M93, L93, and L94 pups. Male and female pups generally grew at the same rate, so male pups remained consistently