Research Document - 2010/137

How many harp seal pups are there? Additional results from the 2008 surveys

By G.B. Stenson, M.O. Hammill et J.W. Lawson


Photographic and visual aerial surveys to determine current pup production of Northwest Atlantic harp seals were conducted off Newfoundland and in the Gulf of St. Lawrence during March 2008. While multiple surveys in the Gulf of St. Lawrence and off southern Labrador provide similar results, visual and photographic surveys of the largest concentration taken on 10 and 16 March, respectively, resulted in estimates that were significantly different (589,400 (SE=49,500 vs. 1,161,600 SE=112,300). A second, lower coverage, photographic survey carried out on 12 March was analyzed in an attempt to reconcile the difference. Nine transects, spaced 14.8 km apart, were flown during this survey, resulting in an estimated pup production of 1,026,997 (SE=280,445, CV=27%). Averaging the two photographic surveys of the Main concentration at the Front resulted in an estimated pup production of 1,142,985 (SE=104,284, CV=9%). Combining this estimate with previously reported estimates of pup production in the southern Gulf (287,033, SE=27,561), the northern Gulf (172,482, SE=22,287), and small group at the Front (23,381, SE = 5,492), resulted in an estimate of total pup production (rounded to the nearest hundred) in 2008 of 1,630,300 (SE=110,400, CV=6.8%). This is significantly higher than estimated previously and is inconsistent with previous predictions obtained from the harp seal population model. Incorporating reproductive rates obtained from annual samples directly into the model may provide some explanation for the large increase in estimates of pup production.

Key words: harp seal, Pagophilus groenlandicus, pup production, survey, abundance, Northwest Atlantic, digital photography.

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