NAFO Sci. Coun. Studies, 26: 105–114 Pup Production of Hooded Seals ( Cystophora cristata ) in the Northwest Atlantic G. B. Stenson, R. A. Myers and W. G. Warren Department of Fisheries and Oceans, Science Branch P. O. Box 5667 St. John's, Newfoundland, Canada A1C 5X1 and I-H. Ni Dept. of Biology, Hong Kong University of Science and Technology Clearwater Bay, Kowloon, Hong Kong Abstract Pup production of hooded seals ( Cystophora cristata) in two whelping concentrations along the northeast coast of Newfoundland (the 'Front') during March 1990 was estimated using systematic visual surveys. In addition, independent estimates of production in one of the concentrations and the number of pups born outside the whelping concentrations were obtained from photographic surveys. Photographic estimates were corrected for incorrectly identified pups by comparing black and white photographs with ultra-violet imagery. Estimates were also corrected for pups absent from the ice at the time of the survey using distinct age-related developmental stages. Approximately 91% of the pups born in the first whelping concentration, and 92% born in the second, were present during the surveys. Based on visual surveys, the corrected pup production in these patches was estimated to be 48 684 (SE = 2 747). Photographic surveys resulted in an estimate of 33 498 (SE = 12 450) pups born outside of the whelping patches, although this estimate could not be corrected for the absence of pups due to the temporal distribution of births. Thus, total pup production was estimated to be 82 182 (SE = 12 636). Comparison with estimates made in the mid-1980s suggest that pup production may have increased although they are not statistically different due to the imprecise nature of the estimates. Key words : Abundance, hooded seals, Northwest Atlantic, pup production Introduction The hooded seal ( Cystophora cristata) is one of the most abundant, pelagic phocids in the North Atlantic. Although some give birth (whelp) on the pack ice north of Iceland, near Jan Mayen Island in the eastern Atlantic, the majority are found in the Western Atlantic where they undergo annual migrations between whelping areas along the coast of Canada and in Davis Strait, and moulting and summer areas off southeast and west Greenland. In the Northwest Atlantic, whelping occurs in the Davis Strait, off Newfoundland and in Gulf of St. Lawrence. Of these, the largest whelping concentration occurs off the coast of southern Labrador or northern Newfoundland (the 'Front'). Using catch data, pup production at the Front was estimated to be approximately 30 000 in the late- 1960s (Øritsland and Benjaminsen, MS 1975; Sergeant, MS 1976; Lett, MS 1977; Winters and Bergflødt, MS 1978). In 1984, pup production at the Front was estimated to be 62 000 (95% CI 43 700– 89 400; Bowen et al ., 1987), based on aerial surveys. Although not directly comparable to earlier studies, this estimate was substantially higher, suggesting that either previous estimates were negatively biased or that the population was increasing. Commercial hunting of hooded seals at the Front has been reported since the 19th century, but likely occurred earlier. Between 1974 (when quotas were first implemented) and 1982, the average annual catch was 12 500 animals, the majority being pups taken by large vessels at the whelping patch (Anon., MS 1994). Following the demise of this hunt in 1983, catches declined to an average of 650 seals per year between 1983 and 1990. This decline in hunt-related mortality may have resulted in an increased population since the 1984 survey. In addition to understanding hooded seal population dynamics, estimates of abundance are necessary in order to determine the potential impact of this species on fish stocks in the Northwest Atlantic. Hooded seals inhabit the Newfoundland continental shelf for much of the winter and spring (Stenson and Kavanagh, MS 1992; Stenson, unpubl.