Monster Seminar JAM - Age-specific survival, abundance and immigration rates of a Weddell seal (Leptonychotes weddellii) population in McMurdo Sound, Antarctica
Dr. Michael F. Cameron, National Marine Mammal Laboratory, NOAA Fisheries
Since the 1960s, Weddell seals (Leptonychotes weddellii) have been tagged and surveyed annually in McMurdo Sound, Antarctica. The resulting long-term data set is invaluable for analyses investigating the variation in their population dynamics. Mark-recapture analyses and model selection trials using Akaike's Information Criterion indicate that sex, cohort and year affect juvenile (ages 1 and 2) Weddell seal survival. In contrast, year, and perhaps sex and cohort, are less important factors of adult survival. The average annual survival is higher among adults (0.92) than juveniles (0.55) and there is little evidence for senescence to at least age 17. Population growth calculations using a Lotka-Leslie based model suggest that the size of the resident population is stable despite annual fluctuations in Jolly-Seber abundance estimates. We argue that this temporal variability is likely the result of temporary immigration--estimated from a simulation model at 16.8% for females. Sea ice extent is proposed to affect such immigration where, during times of reduced fast ice, immigrants are forced from surrounding locations into the ice covered areas of Erebus Bay. Our results contradict previously published estimates of lower survival and higher immigration. Model choice is shown to be the most likely cause of these discrepancies and we provide evidence that our models are more appropriate than those used elsewhere.
Date and Time:
April 1, 2004,
11:00 am - 12:30 pm