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Sources of Variability in Aerial Survey Counts of Harbour Seals on Haul-out Sites in the Bay of Fundy

G. Mark FowlerWayne T. StoboBedford Institute of OceanographyCanada. Department of Fisheries and Oceans

出版	Fisheries and Oceans Canada, 2005
URL	http://books.google.com.hk/books?id=ph5QAQAAMAAJ&hl=&source=gbs_api

註釋Multiple aerial censuses were conducted of a major harbour seal (Phoca vitulina) haulout area off Grand Manan, New Brunswick, Canada, during the molting period to quantify sources of variability in aerial survey counts. Counts increased and decreased with local time, with peak counts between 1200-1600 EST. Low tide may have functioned as a delimiter to this relationship by degree of emergence of haul-out sites, assuming competition for space between seals, but the apparent effect could be an alias for cumulative survey disturbance or progression through the molt period. Hot days appeared to depress counts. Standard deviations of counts made between 1200-1600, computed independently for each day to negate tide or disturbance effects, ranged from 3.7 to 7.5% of the mean. We estimated the proportion of seals in the water during peak haul-out at 20% of the opulation. Photographic counts usually exceeded visual counts, but the difference extended to counts of small groups of animals unlikely to have been visually miscounted. The results (visual counts) of the aerial census study were used to derive correction factors for seals in the water and time of day. These correction factors were applied to earlier estimates of total Bay of Fundy area harbour seal abundance derived from aerial surveys in 1986 and 1992 (adjusted abundances of 2 362 and 4 218 harbour seals respectively). The earlier surveys were also used to adjust the 1995 study to provide a total abundance estimate for the Bay of Fundy (5446 harbour seals). A growth curve fitted to the three point estimates for 1986, 1992 and 1995 suggested abundance increased at a rate of 9.3% per year