Abundance Estimation of a Dispersed, Dynamic Population: Hooded Seals (Cystophora cristata) in the Northwest Atlantic

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Abstract
Pup production of hooded seals (Cystophora cristata) in the Northwest Atlantic was estimated by aerial survey. Simultaneous surveys and the collection of ground-truth data were conducted in March 1984 in both major whelping areas, namely the floe ice in the Davis Strait and off northeastern Newfoundland (the Front). Abundance estimates were obtained from both fixed-wing photographic and helicopter sighting surveys using a strip survey method for unequal-sized sampling units. These abundance estimates were corrected to account for pups which had left the ice and those pups which had yet to be born in each area. A maximum likelihood method was used to combine estimates of abundance from several surveys with estimates of the number of pups in each developmental stage to obtain an estimate of total production. This method weighted each survey point estimate of abundance by the estimated sampling variance and each estimate of the proportion of pups on the ice in each stage by the sample size corrected for loss of degrees of freedom associated with the sampling design. Total production at the Front was estimated to be 62 400 with 95% confidence limits of 43 700 to 89 400 and in the Davis Strait was 19 000 with a 95% confidence interval of 14 000 to 23 000. Total pup production estimates for the Front and Davis Strait are likely underestimates for several reasons, but are substantially higher than those previously assumed for the Northwest Atlantic.

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