EFFECTS OF TIME-DEPTH RECORDERS ON MATERNAL FORAGING AND ATTENDANCE BEHAVIOR OF ANTARCTIC FUR SEALS (ARCTOCEPHALUS-GAZELLA)

We evaluated the difference in average durations of foraging trips and nursing visits to shore between one group of female Antarctic fur sea ls (Arctocephalus gazella) carrying radio transmitters only and anothe r group carrying time-depth recorders (TDRs) and radio transmitters du ring their first five postpartum foraging trip - nursing visit cycles. Data were collected from 105 different fur seals in five breeding sea sons (1989-1990 to 1993-1994) on Seal Island, Antarctica. Average fora ging-trip and nursing-visit durations were significantly greater for t he seals carrying TDRs and radio transmitters than for seals carrying radio transmitters only (two-way ANOVA, year x instrument type; trip, P = 0.004; visit, P = 0.04). Historically, instrument-effect studies o n marine animals have focused on smaller species and larger instrument to body size ratios. Because of small sample sizes (the number of ins truments successfully deployed and retrieved) and the typically variab le nature of data from TDRs, the statistical power to detect significa nt differences due to instrument effects has been low. The evidence of instrument effects on Antarctic fur seals has possible implications f or studies utilizing devices attached to similar-sized animals: result s may not be representative of the natural (non-instrumented) populati on.