ROBERT A. GARROTT
Professor Fish and Wildlife Management
Ecology Department--Montana State University
Office Phone: (406) 994-2270 FAX: (406) 994-3190 e-mail: rgarrott@montana.edu
Variation in recruitment of Weddell seals in Erebus Bay, Antarctica
Gillian Hadley with Jay Rotella and Robert A. Garrott
To
understand population regulation of long-lived species, it is critical to
investigate the relative contribution of various demographic rates to the
overall population growth rate. It is also necessary to identify sources of
variation in these demographic rates, and explore the mechanisms linking the
sources of variation to population changes. Recruitment, in particular, is a
parameter of interest as it allows insight into variation in quality among
individuals in a population. In marine mammals, which typically have low
reproductive rates and delayed sexual maturation, our knowledge of recruitment
is limited due to the challenges in obtaining the requisite long-term datasets.
The first objective of our research will be to explore sources of observed
variation in annual recruitment rates for Weddell seals in McMurdo Sound,
Antarctica. We will determine the extent to which recruitment probability varies
with individual characteristics (colony of birth, timing of birth, experience of
mother, age, and/or cohort).
Additionally, an understanding of population dynamics in long-lived species can provide information about environmental change. If mechanisms of population regulation are understood, we can gain insight into how environmental change translates through the food web into population fluctuations for top-trophic-level vertebrates. Few studies on marine mammals have attempted to link environmental covariates to variation in vital rates. A second objective of our research is to determine how environmental factors (sea-ice extent and concentration, primary productivity) contribute to variation in total annual recruitment to the Erebus Bay population.
Weddell seals have been tagged in Erebus Bay since 1969, and resighting censuses have been conducted annually since 1973. To address our research questions, we will utilize data from this long-term mark-resight database. Multi-state mark-recapture models will be employed in order to 1) estimate survival, sighting, recruitment, and breeding probabilities, and 2) estimate the effects of both individual characteristics and environmental factors on recruitment rates.
Funding: National Science Foundation