ICES Journal of Marine Science, 63: 95e104 (2006) doi:10.1016/j.icesjms.2005.07.005 Estimation of harp seal (Pagophilus groenlandicus) pup production in the North Atlantic completed: results from surveys in the Greenland Sea in 2002 Tore Haug, Garry B. Stenson, Peter J. Corkeron, and Kjell T. Nilssen Downloaded from https://academic.oup.com/icesjms/article/63/1/95/625803 by guest on 27 September 2021 Haug, T., Stenson, G. B., Corkeron, P. J., and Nilssen, K. T. 2006. Estimation of harp seal (Pagophilus groenlandicus) pup production in the North Atlantic completed: results from surveys in the Greenland Sea in 2002. e ICES Journal of Marine Science, 63: 95e104. From 14 March to 6 April 2002 aerial surveys were carried out in the Greenland Sea pack ice (referred to as the ‘‘West Ice’’), to assess the pup production of the Greenland Sea population of harp seals, Pagophilus groenlandicus. One fixed-wing twin-engined aircraft was used for reconnaissance flights and photographic strip transect surveys of the whelping patches once they had been located and identified. A helicopter assisted in the reconnaissance flights, and was used subsequently to fly visual strip transect surveys over the whelping patches. The helicopter was also used to collect data for estimating the distribution of births over time. Three harp seal breeding patches (A, B, and C) were located and surveyed either visually or photographically. Results from the staging flights suggest that the majority of harp seal females in the Greenland Sea whelped between 16 and 21 March. The calculated temporal distribution of births were used to correct the estimates obtained for Patch B. No correction was considered necessary for Patch A. No staging was performed in Patch C; the estimate obtained for this patch may, therefore, be slightly negatively biased. The total estimate of pup production, including the visual survey of Patch A, both visual and photographic surveys of Patch B, and photographic survey of Patch C, was 98 500 (s.e. Z 16 800), giving a coefficient of variation of 17.9% for the survey. Adding the obtained Greenland Sea pup production estimate to recent estimates obtained using similar methods in the Northwest Atlantic (in 1999) and in the Barents Sea/White Sea (in 2002), it appears that the entire North Atlantic harp seal pup production, as determined at the turn of the century, is at least 1.4 million animals per year. Ó 2005 International Council for the Exploration of the Sea. Published by Elsevier Ltd. All rights reserved. Keywords: abundance, aerial surveys, birth distribution, Greenland Sea, harp seal, pup production. Received 6 July 2004; accepted 23 July 2005. T. Haug, P. J. Corkeron, and K. T. Nilssen: Institute of Marine Research, PO Box 6404, N- 9294 Tromsø, Norway. Current address for P. J. Corkeron: Bioacoustics Research Program, Cornell Laboratory of Ornithology, 159 Sapsucker Woods Road, Ithaca, NY 14850, USA. G. B. Stenson: Science Branch, Department of Fisheries and Oceans, Northwest Atlantic Fisheries Centre, PO Box 5667, St. John’s, Newfoundland, Canada A1C 5X1. Correspondence to T. Haug: tel: C47 776 09722; fax: C47 776 09701; e-mail: [email protected]. Introduction examined using cranial measurements (Yablokov and Sergeant, 1963), underwater vocalizations (Perry and Three populations of harp seals, Pagophilus groenlandicus, Terhune, 1999), serum transferrins (Møller et al., 1966; inhabit the North Atlantic Ocean (Sergeant, 1991). Whelp- Nævdal, 1966, 1969, 1971), blood serum proteins (Borisov, ing occurs on the pack ice off eastern Newfoundland and in 1966), allozymes (Meisfjord and Nævdal, 1994), and DNA the Gulf of St. Lawrence (the Northwest Atlantic (Meisfjord and Sundt, 1996; Perry et al., 2000). These population), off the east coast of Greenland (the Greenland studies have revealed significant differences between the Sea or West Ice population), and in the White Sea (the Northwest Atlantic population on the one side and the Barents Sea/White Sea population). Relationships among Greenland Sea and Barents Sea harp seal populations on the three North Atlantic populations of harp seals have been the other, while no evidence of difference between the latter 1054-3139/$32.00 Ó 2005 International Council for the Exploration of the Sea. Published by Elsevier Ltd. All rights reserved. 96 T. Haug et al. two was observed. Recent observations from satellite tagging production should be conducted periodically, preferably experiments suggest that Greenland Sea and Barents Sea with 5 or less years between two consecutive surveys, and harp seals overlap in their feeding range during summer and that efforts should be made to ensure comparability of autumn (JuneeOctober) in the northern Barents Sea (Folkow survey results (ICES, 1994, 2004; NAFO, 1995). et al., 2004). Also, recaptures from tagging experiments, Recent estimates of harp seal pup production are available using traditional flipper tags, suggest that mixing of for the Northwest Atlantic (997 900, s.e. Z 102 100, obtained immature animals between the West Ice and Barents Sea in 1999; Stenson et al.,2003) and Barents Sea/White Sea populations may occur, but there is no evidence of mixing on (330 000, s.e. Z 34 000, obtained in 2002; ICES, 2004) pop- the breeding grounds (Øien and Øritsland, 1995). ulations. Subsequent assessments, done by fitting population Estimating abundance and monitoring changes in models to the independent estimates of pup production (e.g. population size is critical for the management of harp Healey and Stenson, 2000; ICES, 2001, 2004), suggest that Downloaded from https://academic.oup.com/icesjms/article/63/1/95/625803 by guest on 27 September 2021 seals and to understand their role in the North Atlantic the total size of these two populations combined may now be ecosystem. Harp seals are the most abundant pinniped in approximately 7.5 million animals. There are no current the North Atlantic, where they are the focus of the largest estimates of harp seal pup production in the Greenland Sea. marine mammal harvest in the world. Although the three Greenland Sea harp seals were surveyed aerially in 1991, populations have historically been exploited and managed giving a combined estimate of 55 270 (CV 0.141) pups for separately, the combined total reported harvest (conducted four detected and surveyed patches (Øritsland and Øien, by Canada, Greenland, Norway, and Russia) in 2002 was 1995). Obtaining updated information on pup production is approximately 450 000 animals (ICES, 2004). Thus, there needed to assess the status of the Greenland Sea harp seal is considerable interest in assessing the status and population. Consequently, aerial surveys were carried out monitoring changes in abundance in all three populations in 2002 during their whelping (pupping) period (Marche in order to manage the respective harvests responsibly. In April). The surveys were carried out using techniques addition, knowledge of harp seal population size is one similar to those developed and used previously to determine factor required in order to estimate the potential influence pup production for harp seals in the Northwest Atlantic of this species on other marine organisms, including (Stenson et al., 1993, 2002, 2003), in the Greenland Sea commercially important fish species. Harp seals are (Øritsland and Øien, 1995), and in the White Sea (Potelov important predators, and may also play a role in et al., 2003; ICES, 2004). Standardization of methodology structuring ecosystems, both in the Northwest (Hammill and interpretation of results were achieved by involving and Stenson, 2000; Bundy, 2001) and Northeast (Nilssen scientists from Canadian, Norwegian, and Russian institu- et al., 2000) Atlantic. For example, in Atlantic Canada tions in both fieldwork and subsequent analyses of data. waters harp seals accounted for over 80% of the estimated Although there were some small differences between surveys, 4 million tonnes of fish and zooplankton consumed by all the results from all areas are comparable and facilitate an seal species in the area (Hammill and Stenson, 2000). updated ‘‘turn-of-the-century’’ estimate of the total pup Annual consumption by Barents Sea/White Sea harp seals production of harp seals in the entire North Atlantic based on was calculated by Nilssen et al. (2000) to be of sampling over a restricted time period (1999e2002). a magnitude of 3.5 million tonnes, of which various fish species constituted well over 2 million tonnes e an amount comparable with the quantities of fish consumed Material and methods annually by cod Gadus morhua, the main upper-level predator of the Barents Sea (Bogstad et al., 2000). Reconnaissance surveys Due to uncertainties in the assumptions required when Whelping concentrations were located using fixed-wing and estimating abundance from catch-at-age data and sequential helicopter reconnaissance surveys of areas historically used population models, total abundance of a population is by harp and hooded seals in the Greenland Sea, mainly the estimated by fitting a population model using age-specific pack ice areas along the eastern coast of Greenland between reproductive rates and catches to the independent estimates 67(30#N and 74(40#N(Figure 1). Surveys were carried out of pup production (e.g. ICES, 2004). Although mark- between 14 March and 5 April 2002 at altitudes between recapture techniques have been used previously (e.g. 800 and 1000 ft. Reconnaissance flights using the fixed- Bowen and Sergeant, 1983; Øien and Øritsland, 1995), wing aircraft were generally flown as repeated systematic the use of aerial photographic and visual surveys represents eastewest transects spaced 10 nm apart, from the ice edge an alternative and industry independent approach to in the east into the dense drift ice closer to the Greenland estimate harp seal pup production that has been used shore. Due to ice drift and variation in pupping dates (mid to successfully both in the Northwest Atlantic (Stenson et al., late March, see Øritsland and Øien, 1995), most areas were 1993, 2002, 2003), in the Greenland Sea (Øritsland and surveyed repeatedly to minimize the chance of missing Øien, 1995), and in the White Sea (Potelov et al., 2003; whelping concentrations.