Mark–Recapture Estimates of Harp Seal Pup (Phoca groenlandica) Production in the Northwest Atlantic

Pup production of the northwest Atlantic harp seal population (Phoca groenlandica) was estimated using a modified Petersen model corrected for tag loss and nonreporting of recovered tags. Variance estimates were corrected for the additional sources of variation due to tag loss, reporting rate, and the estimation of the number of seals examined for tags. Experiments were conducted in March of 1978, 1979, and 1980 with 9154, 4939, and 6246 pups being tagged in each year, respectively. Estimates from short-term recoveries (within the same year) were unreliable because of failure to satisfy the assumption of uniform mixing of marked and unmarked seals. Pooled estimates from long-term recoveries (1–3 yr) were considered more reliable, with the 1978 estimate of 506 000 ± 77 000 (1 SE) and the 1979 estimate of 489 000 ± 71 000 being most reliable. Based on the results of this study and on the trend in catches of pups and immatures in West Greenland, we conclude that harp seal pup production and hence population size has probably increased since the imposition of catch quotas in 1971.