Population dynamics of Weddell seals (Leptonychotes weddelli) in McMurdo Sound and the Victoria Land Coast: movement in the area, sub-adult populations, age structure and reproductive condition

The population parameters of the Weddell seal in McMurdo Sound was initiated in the 1965-66 season following a 4 year study of the reproductive cycle of the Weddell seal and 2 years of tagging by the USARP. Secondary objectives of the study include assessment of the effects of fluctuations of environmental conditions upon daily activities and the onset of pupping and to study the behaviour of the Weddell seal. To study a population it is essential to determine how discrete it is. The study area was defined at the West coast of Ross Island between Scott Base and Cape Royds including the Dellbridge Islands. From the 1962-63 to the 1965-66 seasons, branding of seal pups was carried out. After this period, tagging of all seal pups and selected adults was the main method of marking individuals. Data on birth rate, longevity, life expectancy of the various age classes, dispersal, overall numbers and daily and seasonal movements were collected over several seasons. To check on possible movements of individuals into or out of the study area, trips were taken to other areas to look for tagged seals from the study area and to tag seals to see if they come to the study area. Several sites along the Victoria Land coast as far north as Cape Hallett were visited including, but not restricted to, Franklin Island, Cape Hallett, Cape Crozier, Cape Bird, Marble Point, Strand Moraines, White Island and various other sites. Sub-adult seals are absent from the study area. Reasons for this may be that they are residents in the pack ice or along the northern coast until returning to the breeding sites as adults. To determine if this is true, observations were collected via ship and quantitative census via helicopter at five sites on the Victoria Land Coast. Aerial censuses were carried out from helicopter to follow the build up of total numbers of seals and the seasonal population shift. To calculate the survival and productivity of the population, data on the age structure and reproductive condition of the population was facilitated by the collection of canine teeth and reproductive organs from seals killed for dog food at Scott Base (this practice ended in the 1980's) and from dead carcasses.