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Juvenile Steller Sea Lions Captured for Foraging Behavior and Health Studies
Scientists from the National Marine Mammal Laboratory (NMML) Alaska Ecosystems Program have been conducting studies of juvenile Steller sea lion (Eumetopias jubatus) foraging ecology and health status in the Gulf of Alaska and Aleutian Islands to test hypotheses of mechanisms underlying Steller sea lion population declines and to test the efficacy of fisheries management actions. Twenty-five juvenile sea lions were captured at haul-out sites from Kodiak Island and the eastern Aleutian Islands from 24 February to 14 March using a combination of scuba-based underwater and on-land hoop net capture techniques (Fig. 1 above). The capture cruise, conducted on board the U.S. Fish and Wildlife research vessel Tilax, was coordinated with echo-integration and trawl surveys of groundfish and other fish biomass in the Umimak Pass/Bering Sea and Kodiak Island areas by the AFSC Midwater Assessment and Conservation Engineering Program (MACE) and in the Chiniak Gully and Long Island areas by several projects through the University of Alaska.
Satellite-linked depth recorders (SDRs) were attached to each sea lion
to track movements and record diving behavior, from which foraging behavior
and changes associated with weaning are inferred. In addition to being
outfitted with SDRs, sea lions were weighed, measured, and given complete
physical exams. Blubber biopsies were taken for fatty acids and contaminants
analysis, and skin samples taken for genetics analysis. Blood samples
were taken for subsequent clinical health determinations. Two sea lions
captured, sampled, and instrumented during the cruise had been previously
tagged as pups (at Chowiet Island and Ugamak Island) in 2001, thus providing
additional critical life history information such as growth rate. All
25 sea lions were estimated to be 9 months of age at the time of capture.
Because some pups may wean at about 11 months of age, the SDR data could
provide unique insights as the pups learn to become independent foragers.
Even at this age, however, there are a variety of movement patterns among
pups. Figure2 below shows the locations of ten pups instrumented near Unimak
Pass, one of which made several forays into deeper waters while the others
remained closer to islands.
In addition to these captures, scats were collected at two sites in the eastern Aleutian Islands for food-habits analysis, and two aborted fetuses were found and necropsied. Sightings were made of 23 sea lions tagged or branded as pups on rookeries or as juveniles during previous capture trips, which will be used to infer long-term movements and contribute to estimates of survival.
By Brian Fadely.
NMFS observers documented the Eastern North Pacific gray whale southbound migration from 12 December 2001 to 5 March 2002 at Granite Canyon, California. This followed the unexpectedly low counts and irregular migratory timing from the previous winter. Seasonal sighting distributions are usually represented by a symmetrical, bell-shaped curve, but in 2000-01, the distribution was very irregular, and whales continued migrating south more than 3 weeks later than in any previous season. It was unclear whether the low counts were caused by the irregularity of the migration (possibly, many whales did not migrate as far south as central California), or if there really was a major drop in abundance. For three decades, abundance estimates had been steadily increasing at 2.5% from about 12,000 in 1967-68 to 26,600 in 1997/98. However, in both 1999 and 2000, there were 200-300 dead gray whales stranded on beaches from Mexico to Alaska, well above an average of 38 per year. During those two years, calf counts were unusually low, and adults were visibly skinny even from a distance. The preliminary abundance estimate for 2000/01 was under 19,000 about 7,000 less than the previous years estimate.
To maximize interyear compatibility, research protocol in 2001-02 was essentially identical to that used in previous surveys. Single observers independently searched for whales and recorded data on time, location of sightings, count, direction, and environmental conditions. The counting system and observer performance were tested through paired, independent observer effort. In addition, observations made with high-power (25X) binoculars provided an index of the offshore distribution of migrating whales passing within the sighting range of the observers. Last winters migratory timing was typical of most observed migrations: the sighting distribution appeared as a nearly symmetrical bell-shaped curve centered on 16 January and most sightings occurred in January and early February. More pods were counted in 2001/02 than in the previous year (1,689 in 2000/01 versus 1,711 in 2001/02), but when correction factors were applied, the abundance estimate was only about 17,500. Although this may appear at first to be a continuing decline, the past two seasons abundance estimates are not statistically different. Instead, scientists suspect that what may be happening is a recovery in the population following a catastrophic event in 1998 and 1999, the details of which we may never fully understand. Since then, the whales have looked healthier, stranding rates have dropped, and calf counts (this winter) have rebounded.
By Dave Rugh.
The Polar Ecosystems Program conducts annual surveys of harbor seal haul-out sites in Alaska to estimate population abundance and distribution. Although observer-based aerial surveys have been effective for counting seals that haul out on sand and rock habitats, it is estimated that up to 20% of seals in the Gulf of Alaska (GOA) haul out on ice floes in glacial fjords. These sites present a challenge to standard aerial survey techniques because the topography of the fjords and glaciers often preclude low-level flights, the ice floes are dispersed and mobile, and glacial ice is sometimes dirty, making it difficult to detect and count seals.
To overcome these problems, the NMML contracted an aerial survey company in Anchorage, Alaska, to survey 14 glacial sites in the GOA, Prince William Sound, and Kenai Peninsula, using large-format (23X 23 cm) photography linked to a GPS (global positioning system) mapping system. During August-September 2001, each site was photographed two or three times, at altitudes ranging from 610 m to 1,463 m, producing more than 1,200 photographic negatives. To transform the negatives into a medium suitable for quantifying seals and ice habitat, the Polar Ecosystems Program developed an image analysis facility that includes a large-format scanner and other specialized equipment and software for processing the large-format imagery. First, negatives are scanned at high resolution (1,600 dpi), so that seals are plainly visible when the images are enlarged. Next, a GIS (geographic information system) based imaging software application is used to georectify (i.e., assign GPS coordinates) the resulting images and create a seamless mosaic of images for each glacier site. This process will allow a more accurate estimate of the number and distribution of seals by ensuring that all available habitat is surveyed and that no seals are counted twice.
By Alana Phillips and John Bengtson.
West Coast Pinniped Meeting
The West Coast Cooperative Pinniped Program met 14-15 March 2002 in Clackamas,
Oregon, to discuss issues of expanding harbor seal and California sea lion
populations in Washington, Oregon and California. A total of 20 participants
attended representing the NMML, Northwest Fisheries Science Center, Southwest
Fisheries Science Center, Northwest Region (NWR), Southwest Region, Moss
Landing Marine Laboratory, Washington Department of Fish and Wildlife,
Oregon Department of Fish and Wildlife, and Pacific States Marine Fisheries
Commission. Participants reported on population assessment of harbor seals
and California sea lions (including life history parameters and genetics),
pinniped food habits and predation on Endangered Species Act
salmonids in Washington (Hood Canal, Lake Ozette, Columbia River), Oregon
(Rogue River, Alsea Bay, Willamette Falls), and California (Scott Creek,
Ano Nuevo Island, San Lorenzo, Klamath, Eel, Mad and Smith Rivers).
In early February 2002, researchers from the California Current Ecosystem Program went to San Miguel Island to evaluate brands and general health of California sea lion pups branded in September 2001 as part of a long-term study begun in 1987 to assess the health, vital parameters, and population trends of the California sea lion population.
In mid-February 2002, the JASON Project, an educational outreach program that develops science curriculum for grades 7-12, filmed California sea lion and northern elephant seal behavior at San Miguel Island, California. Bob DeLong and Tony Orr assisted the JASON staff with developing curriculum related to the natural history of seals and seal lions to be distributed to classrooms during the 2002-2003 school year.
On 2 January 2002, staff from NMML and other Northwest regional agencies, plus numerous other killer whale scientists responded to the stranding of two killer whales in Dungeness Bay, Washington. A dead 20-ft adult female was necropsied, but several analyses are still pending to determine cause of death. A 21-ft adult male was successfully released. Data from a suction-cup attached time-depth recorder showed normal diving behavior for 3 days post-release (until the tag memory was filled) indicating the male survived. Both whales were identified as transients and had been observed only once previously off the coast of Oregon in 1996.
During mid- to late January 2002, a lone juvenile female killer whale was routinely observed in the vicinity of the Fauntleroy- Vashon Island ferry route in Puget Sound, Washington. Concerns about the animals health arose because she was alone, was somewhat underweight, and had an extensive skin disease. NMML staff worked with other killer whale researchers to identify her as A73, a member of a northern resident pod, none of which have ever been known to range into this area of Puget Sound. She may have strayed from her pod because her mother was missing from the A4 group in 2001 and may have died. A73s extensive skin disease, body condition, and propensity to approach boats led NMML staff to work with other researchers and veterinarians to assess her health status using behavioral data and respiratory gas samples. Although the whale had been observed to pursue and capture salmonids on several occasions and appeared to be maintaining her weight, her variable activity levels and high ketone content in the respiratory gas samples indicated the need for an ongoing assessment of her health status. NMML staff worked with other NMFS staff readying logistical plans should intervention be necessary.
By Harriet Huber.
Auke Bay Lab