Harbour seal (Phoca vitulina) COSEWIC assessment and status report: chapter 7

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Population Sizes and Trends

There are no range-wide estimates of the abundance of P. v. concolor or P. v. mellonae in Canada. Much of the range of both designatable units (DUs) has never been surveyed. Range-wide trends in abundance cannot be calculated.

Phoca vitulina concolor

Boulva and McLaren (1979) estimated 12,400 harbour seals in Canadian Atlantic waters in 1973 (excluding Labrador), with most found on Sable Island and the Atlantic coast of Nova Scotia (5,250). The population is estimated to have declined at a rate of approximately 4%/year between 1950 and 1973 because of bounty kills (Boulva and McLaren 1979; Malouf 1986). Hammill and Stenson (2000) calculated that if the population had continued to decline at 4% per annum until 1976, when the bounty program ended, and thereafter increased at 5.6% per annum, the population size in 1996 would be 31,900, but it is generally acknowledged that no reliable abundance estimate currently exists for the harbour seal population in eastern Canada (Anonymous 2003).

The count of animals hauled out on Sable Island in the summer of 2004 was approximately 150, a population size that has remained fairly stable in recent years (Bowen 2005). However, the population had previously undergone a large decline (Bowen et al. 2003).

Harbour seals were counted on some portions of the New Brunswick coastline of the Bay of Fundy in the autumn and early winter of 1984, 1987 and 1998 (Jacobs and Terhune 2000). Semi-monthly fixed wing aerial and shipboard surveys produced a similar maximum count of just over 1,000 seals in each of the three years of observation. In 1985-87 and 1991-92, Stobo and Fowler (1994) conducted helicopter surveys of harbour seals along some portions of the Bay of Fundy coast on both the New Brunswick and Nova Scotia sides. The maximum number of seals observed was 3,534 in 1992. These are minimum estimates of total population size given that some portion of the population was at sea when the seals were counted on shore.

Generally, the New Brunswick side of the Bay supported greater numbers of harbour seals (84% of the total) than the Nova Scotian side, and the shoals and islands off the seaward coasts of Grand Manan accounted for 53-60% of harbour seals counted during the five surveys. In contrast to the lack of a trend reported by Jacobs and Terhune (2000), Stobo and Fowler (1994) reported that over the 8-year time period of the surveys, the abundance of harbour seals increased on both sides of the Bay, the greatest increase being observed on the New Brunswick side, but cautioned about the uncertainty of their estimated rates of change due to the limitations of the survey design and execution.

Aerial surveys were flown in the St. Lawrence Estuary in June 1995, 1996 and 2000, and in August 1994, 1995, 1996 and 1997 (Robillard et al. 2005). Two surveys were flown in June 1996 and 2001 in complementary areas of the Gulf of St. Lawrence. A 4-hour survey window around low tide was generally respected during surveys of the Estuary with a few exceptions. These surveys did not cover the eastern and northeastern portions of the Gulf of St. Lawrence, though some historical evidence exists of harbour seals in this area (Robillard et al. 2005). Correcting for seals in the water resulted in abundance estimates of 811-1,008 harbour seals in August 1997 and 721-858 animals in June 2000 in the Estuary, 635-757 seals for areas of the Gulf covered in June 1996, and 575-685 seals for those areas covered in June 2001. Combining the count for the two complementary areas of the Gulf, converting them to a density estimate (0.23-0.28 seals/km), and applying this estimate to the unflown portion of the Gulf, resulted in a total of 3,108-3,744 harbour seals in the Estuary and Gulf of St. Lawrence. Adding to this estimate the average of the Estuary accounts resulted in an abundance index of 4,000-5,000 (rounded to the nearest 1,000) harbour seals in the Estuary and Gulf of St. Lawrence. Trends in abundance of harbour seals in the Estuary were examined using the June and August estimates, first considering the study area as a whole, but also the different sectors separately, and four major haul-out sites. With one exception, none of the rates of increase were significantly different from zero, and none of the regression analyses were associated with homogeneous variances. A power analysis indicated that these results were expected given the small sample size. Growth rates varied widely depending on sectors or sites, and were in some cases, larger than the maximum growth rate of 12-13% estimated for pinniped populations not subjected to immigration, and with constraints on reproductive life history typical of harbour seals. Several growth rates approached zero or encompassed zero or negative values in their 95% confidence interval (Robillard et al. 2005).

In Newfoundland, Sjare et al. (2005) conducted boat-based reconnaissance surveys of 7 areas thought to be important for harbour seals between May and September from 2001-2003. Opportunistic shore-based counts from an elevated viewing position were done at a variety of locations, and aerial observations of the northern tip of the Port au Port peninsula were also conducted. Information on the distribution and relative abundance of harbour seals in areas not surveyed by boat, aircraft or shore was collected from interviews with long-time coastal residents and from discussions with experienced hunters participating in the biological collection program. Many areas along the Newfoundland coast were not surveyed, and it is not known what proportion of the population was documented in each of the surveys. Disturbance caused by hunting likely influenced the survey results at St. Pauls Inlet, Point May and Southwest Arm. During 2002 and 2003, three small boat surveys conducted from Renews to Chance Cove Provincial Park counted a maximum number of 164 harbour seals. A maximum count of 296 animals was derived from surveys of a portion of Placentia and St. Mary’s Bays. The maximum count at Point May was 46, and at Pass Island was 24. An aerial assessment north of Port au Port peninsula produced a minimum count of 40 animals in 2003-2004, and five shore-based surveys in the St. Pauls Inlet area produced a maximum count of 88 seals. Compared to Boulva and McLaren (1979), these recent data indicate that abundance at some well known haul-out sites in the more southern portions of the province may have increased while abundance at sites in more northern areas and the northeast coast still remain low relative to the early 1980s. Sjare et al. (2005) caution, however, that a better understanding of annual and seasonal seal movement patterns is needed before any conclusions on site specific and local abundance trends can be made.

Few quantitative data are available for harbour seals in Labrador, save for some anecdotal information regarding a group of as many as 100 seals in the Paradise River near Cartwright, and the observation of as many as 40-50 animals in the Sandy Island area near Natuashish (Sjare et al. 2005).

Along the west shore of Hudson Bay, the only aggregations of animals that have been counted are the 39 seals observed hauled out in the Churchill River in 2003 and 50-60 animals observed along the Seal River in 2002 (Bernhardt 2005).

From the above-noted studies, the total population of harbour seals in eastern Canada numbers at least 10,000 (Table 1). It should be stressed that this estimate is imprecise and likely negatively biased as it includes only portions of the harbour seal’s eastern Canadian range. Moreover, the estimates in Table 1 were obtained using varying methods and are based on surveys of differing degrees of thoroughness. In addition to their fragmentary nature, the existing data – and any trends in abundance – are difficult to interpret given uncertainty related to the degree of discreteness of harbour seal colonies in Atlantic Canada and the northeastern United States (Robillard et al. 2005).

The corrected 2001 abundance estimate for harbour seals in the northeastern United States was 99,340 individuals (Gilbert et al. 2005). Between 1981 and 2001 the uncorrected counts of seals there increased at an annual rate of 6.6%. Approximately 1,200 animals were counted in a 2001 aerial survey between Eastern Bay, Maine and the New Brunswick border. That number does not appear to be increasing in contrast to harbour seals elsewhere in the United States' northeast, leading Gilbert et al. (2005) to speculate on geographic substructure of the population.

Seal numbers at St. Pierre and Miquelon (a French dependency), off the south coast of Newfoundland, appeared to increase between 1970 and 1982 (Ling et al. 1974; Davis and Renouf 1987). Since that time, the summer breeding aggregation at Grand Barachois (Miquelon, 16 km off the south coast of Newfoundland) decreased from a high of 908 animals in 1982 to 200 animals in June 2006 (Lawson 2006). Harbour seals in Greenland have declined substantially over the past few decades, likely as a result of overhunting (Teilmann and Dietz 1994).

Phoca vitulina mellonae

Estimates of the size of this subspecies population are imprecise, though it is clearly a small population.

In three years of intensive summer field work at Lacs des Loups Marins, which all evidence indicates is the core of the P. v. mellonae range, Smith (1999) observed only 39 animals in total, nearly all sightings of single individuals. A maximum of 500 animals was the "guess" of Doutt (1957), cited in Scheffer (1958). Power and Gregoire (1978) estimated 200 and 600 animals by two different summations. The most recent estimate by Consortium Gilles Shooner & Associés et al. (1991) was approximately 100 animals, or 0.1 seals/km², in Lacs des Loups Marins and Lac Bourdel. These two lakes, with the possible addition of Petit Lac des Loups Marins, appear to be the core (and quite possible the sum total) of the current range. There is evidence that the range was larger in the past.

Population trends over time obviously cannot be calculated, though some evidence exists that the population had a larger range, and was more abundant, in the past. During his 1896 traverse of the Ungava peninsula for the Geological Survey of Canada, A.P. Low observed seals in Lacs des Loups Marins and reported that “the Indians kill annually more than thirty, showing that the animal breeds freely in the fresh water” (Low 1898, p. 13). On July 22, 1818, George Atkinson reached the neighbourhood of Petit Lac des Loups Marins and recorded in his journal: “At these ripples is a fishing place where the Indians set nets for seals in the winter; they are quite a different species to those on the sea coast; their skin being covered with short silky hair; yesterday and this day we saw several in the lakes and rivers” (Atkinson 1818). This ease of sighting, and estimate of hunting effort, suggests the population may have been larger than exists today.

Smith and Horonowitsch (1987) quoted an unpublished manuscript from the Arctic Biological Station, which: “Indicates that local knowledge in Ungava Bay pointed to a widespread occurrence of harbour seals in inland lakes which were collectively called Kasigiaksiovik (place of the harbour seal) by the Inuit. The advent of rifle hunting and the high desirability of harbour seal pelts for decorative use probably resulted in a rapid reduction in numbers of harbour seals in both the rivers and lakes close to Inuit hunting grounds” (Smith and Horonowitsch 1987, p. 8). This view that the present-day distribution of harbour seals in lakes in the Hudson Bay-Ungava Bay watershed has been limited by hunting was shared by Mansfield (1967).

The apparent reproductive seasonality of P. v. mellonae (Smith et al. 1994) and the population’s geographic isolation means that any rescue effect from neighbouring oceanic harbour seal populations is improbable. Recolonization is further compounded by the distance from the coast and the current small size of the oceanic populations in both Hudson Bay and Ungava Bay.