THOMAS S. GELATT, Department of Fisheries and Wildlife, University of Minnesota, St. Paul, Minnesota 55108
DONALD B. SINIFF, Department of Ecology, Evolution and Behavior, St. Paul, Minnesota 55108
Long-term examinations of the demographic processes acting on the dynamics of a large mammalian vertebrate are rare throughout the world. It is often necessary to document these factors over a period of time at least as long as a single generation in order to recognize any real differences in the most important members of the population: the breeding adults. An extensive program of tagging and re-sighting Weddell seals in Erebus Bay, near McMurdo Sound, Antarctica, carried out by the Universities of Minnesota and Alaska-Fairbanks since the early 1970s, has permitted in-depth analyses of these processes. This work continued in the 1995-1996 and 1996-1997 field seasons with the primary objectives of updating the extensive database by marking all of the newborn pups and performing weekly censuses within the study area extending from Scott Base to Cape Evans, McMurdo Sound. In addition, the continued monitoring of the survival of individual seals sampled in the early 1990s was requested to permit follow-up investigations by researchers at the University of Alaska.
We used Jolly-Seber mark-recapture functions to estimate the Weddell population in the area by comparing the ratios of marked seals seen in consecutive censuses. These censuses have revealed that the population has remained essentially stable since the last thorough analyses in the mid-1980s (Testa and Siniff 1987). Likewise, the number of pups born annually appears to have leveled out over the previous 14 years.
Our seasons extended from 14 October to 3 December and 10 October to 10 January in 1995-1996 and 1996-1997, respectively. The first pup was tagged on 18 October in both seasons, and in total, 386 pups were tagged in 1995 and 380 in 1996. Two helicopter flights were used in each season to visit the isolated population of seals at White Island approximately 15 kilometers southeast of McMurdo Station. This population is surrounded by the Ross Ice Shelf and recent molecular genetic work suggests that some inbreeding may be occurring (Fleischer, Perry, and Testa 1995, unpublished data). Eight tagged adult females were seen in each season; four pups were tagged in 1995 and eight in 1996. One pup in 1995 and three in 1996 appeared to have died soon after birth. Tissue samples were collected for further genetic analyses and an entire carcass was collected in 1995 for examination at the University of Alaska. Blood samples were collected from pups of various ages, within the study area, in both seasons, for baseline investigations of trace metal and vitamin concentrations.
Blood and tissue samples were also collected in 1996 from all seals at the Big Razorback colony for preliminary work examining the mating system of Weddell seals. We are utilizing recent advances in molecular genetics, which now permit individual identification. Information obtained from the long-term database has shown that Weddell seals have a relatively high fidelity for returning to the study area in subsequent years to breed and give birth. All breeding occurs under the ice and has been observed only once via remote cameras (Cline and Siniff 1971). By sampling mother-pup pairs soon after the pups' birth, however, and comparing these to the males in the same area the previous year, we hope to shed some light on the breeding system and obtain good estimates of male reproductive success as estimated by number of pups produced. The database provides information on maternal lines from the tagging histories of known-age breeding females. Using a combination of molecular genetics, behavioral observations, radio telemetry, and paternity analyses, we have initiated a project to
Preliminary analyses have confirmed the first two objectives. Research is continuing on the third.
In January 1997, we collaborated with scientists from Hubbs Sea World Research Institute to collect blood samples for blood parasite and chemistry analyses. Additionally, we attached four satellite-linked radio transmitters to weaned pups to gather information on the movements of these individuals after the pupping season. Annual census records on individual seals tagged as pups in the study area have shown that nonreproductive animals tend to leave the study area, only to return again when they are reproductively active. Our objective was to track some seals in their first year to compare their movements to the annual ice break-up and to the known range of adult seals. Two of the four transmitters were still collecting locations in September of 1997, and one continued to transmit until early November.
This research was supported by National Science Foundation grant OPP 94-20818 to D.B. Siniff. M. Cameron, R. Jenson, D. Monson, B. Stewart, and P. Yochem provided field assistance
Cline, D.R., and D.B. Siniff. 1971. Underwater copulation of the Weddell seal. Journal of Mammalogy , 52(1), 216-218.
Fleischer, R.C., E.A. Perry, and J.W. Testa. 1995. Do low genetic variation and inbreeding relate to low fecundity in a small, isolated population of antarctic Weddell seals? [Abstract presented at 11th biennial conference on the biology of marine mammals, Orlando, Florida, December 1995.]
Testa, J.W., and D.B. Siniff. 1987. Long-term population dynamics of Weddell seal ( Leptonychotes weddellii ) in McMurdo Sound, Antarctica. Ecological Monographs , 57, 149-165.