Will low sea ice threaten harp seals & polar bears on Canada’s East Coast this year?
Will low sea ice threaten harp seals & polar bears on Canada’s East Coast this year?
polarbearscience / by susanjcrockford / 12h
In early February this year, sea ice was much lower than usual along the Labrador coast and virtually non-existent in the Gulf of St. Lawrence, which are two important pupping habitats for North Atlantic harp seals. The picture would have been very bleak for harp seal pups and the Davis Strait polar bears that depend on them for food if ice hadn’t expanded and thickened by early March – but it did. Past experience suggests that harp seals that usually whelp in the Gulf of St. Lawrence, where ice is still well below average this year, will move to ice off Southern Labrador (‘the Front’) to have their pups.
Harp seal pup_DFO Newfoundland
Sea ice off Labrador/Gulf of St. Lawrence
There is no way to sugar-coat this: there wasn’t much ice off the East Coast in early February, which was shaping up to be as bad or worse than the recent low-ice year of 2011. Below is the weekly ‘departure from normal’ ice chart from the Canadian Ice Service for the week of Feb 1, which shows a lot of area normally covered in ice at this time of year (red) that was still open water:
East Coast weekly departure from normal 2021 Feb 1
However, there was ice further north that has now moved down the Labrador coast from Davis Strait (see below):
Sea ice extent Canada 11 March 2021
At 10 March, there is still much less ice than usual but it appears to be adequate at the Front (southern Labrador coast) for harp seals to have their pups.
Labrador Coast daily stage of development 2021 March 10
However, the pupping grounds won’t be spreading out across the north coast of Newfoundland as they usually do – there simply isn’t the ice there for it:
Newfoundland daily stage of development 2021 March 10
When do harp seals need ice?
The timing sequence for harp seal pupping season in the North Atlantic is White Sea (late February); Gulf of St. Lawrence, aka the “Gulf” (early March, mean 5 March); Labrador/Newfoundland, aka the “Front” (mid to late March, mean 12 March); East Greenland around Jan Mayen Island, aka the “West Ice” (late March to early April). The Jan Mayen/West Ice region is the furthest north that harp seals pup, breed and moult.
Sea ice in the Gulf the week of 8 March 2021 below is not really thick enough for harp seals. They need first year ice (green on the chart), which is sorely lacking in the Gulf this year:
Gulf of St Lawrence daily stage of development 2021 March 10
No difference has been found between harp seals at the Gulf and those at the Front, so together they are treated as one population for management purposes (Sergeant (1991; Stenson 2014). Harp seals are currently more abundant than they have been for decades and are still increasing. Below is a graph showing changes in NE Atlantic harp seal numbers between 1952 and 2019 (DFO 2020):
Harp seal population size NW_1952-2019_DFO March 2020 Fig 8
What kind of ice do harp seals need?
According to Sergeant (1991: 116) :
“…it is possible to categorize the type of ice used by harp seals for whelping (Fig. 127). This is medium winter ice in late February with 6 to 8/10 ice cover, i.e. it must be strong enough but have enough open leads for the seals to penetrate it.” [my bold]
Sergeant (1976:98, 38) pointed out that ice in the Gulf is formed in situ and usually only gets about 40-50cm thick, whereas the ice at the Front is thick first year ice with origins in the far north. This makes Gulf of St. Lawrence ice formation much more susceptible to local conditions (warm OR cold) and thus, the highly variable sea ice conditions are not new (Johnston et al. 2005), a fact corroborated by reports by early 20th century sealers from 1924-1941 (Ryan 2014).
Sergeant (1991: 31) made this point:
“Greatest year-to-year changes are seen in the Gulf of St. Lawrence at the southern margin of the range, where ice in any one season may be thick or almost absent.” [my bold]
What do seals do if there is little ice?
What do harp seals do when ice conditions are poor in the Gulf of St. Lawrence, as has happened often in the past? Sergeant (1991:56) said this:
“In 1981, with almost no ice in the Gulf, mortality of at least several hundred young and tens of adults was seen on the north shore beaches of Prince Edward Island….
Sergeant (1982) found that ice conditions affected whelping patterns markedly in the Gulf of St. Lawrence in 1953, 1969 and 1981, or about one year in ten. In 1969 at least, ice conditions at the Front and in the Strait of Belle Isle were light also and would have allowed adult females which had not whelped in the Gulf to search northward for ice; some may have done so.
[in 1969] There was no ice in the Gulf except in Northumberland Strait and shore ice on the north coast of Prince Edward I. It was generally agreed that no more than 40 000 animals whelped here… The number at that time expected to whelp in the southern Gulf was ca. 100 000.
East coast ice stage of development weekly at 10 March 1969
Probably, the remainder searched for ice, and finding none in the northern Gulf, passed through the Strait of Belle Isle and whelped together with the Front herd on the coast of Labrador at Hamilton Inlet.
In 1981, however, although ice was of minimal extent and thickness in the Gulf, harp seals whelped off the west coast of the Magdalen Is. and drifted to the north coast of Prince Edward I. Here storms destroyed the small amount of ice and young harp seals died due to starvation and loss of body reserves (Dr. J.R. Geraci, in litt.).
East coast ice stage of development weekly at 10 March 1981
Under unusually heavy ice conditions, it is not possible for harp seals to move from the Front to the Gulf before whelping, since the Strait of Belle Isle is then blocked by ice. Whelping merely occurs further south along the east coast of Newfoundland.” [my bold]
However, polar bears have rarely penetrated into the Gulf in recent heavy ice years: they stick to eating seal pups on the ice at the ‘Front’ off Newfoundland and Labrador.
What have recent low ice years looked like?
The worst year for low ice on the east coast in recent decades was in 2011 (Stenson et al. 2015), see below, for the week of 31 January:
East coast ice stage of development weekly at 31 Jan 2011
Comparing the above to this year for the week of 1 Feb (below) shows the remarkable similarity:
East Coast weekly stage of development 2021 Feb 1
Department of Fisheries and Oceans Canada (DFO) 2012. Current status of northwest Atlantic harp seals (Pagophilus groenlandicus). Science Advisory Report 2011/070.
Department of Fisheries and Oceans Canada DFO. 2014. Status of Northwest Atlantic harp seals, Pagophilus groenlandicus. DFO Can. Sci. Advis. Sec. Sci. Advis. Rep. 2014/011.
DFO. 2020. 2019 Status of Northwest Atlantic Harp Seals, Pagophilus groenlandicus. DFO Can. Sci. Advis. Sec. Sci. Advis. Rep. 2020/020. http://www.isdm-gdsi.gc.ca/csas-sccs/applications/Publications/result-eng.asp?params=0&series=7&year=2020 PDF here.
Johnston, D.W., Friedlaender, A.S., Torres, L.G., Lavigne, D.M. 2005. Variation in sea ice cover on the east coast of Canada from 1969-2002: climate variability and implications for harp and hooded seals. Climate Research 29:209-222.
Kovacs, K.M. 2015. Pagophilus groenlandicus. The IUCN Red List of Threatened Species 2015: e.T41671A45231087. http://dx.doi.org/10.2305/IUCN.UK.2015-4.RLTS.T41671A45231087.en
Ryan, S. 2014. Appendix 3: Chafe’s “Notes of the Voyages” 1924-1941, In: The Last of the Ice Hunters: An Oral History of the Newfoundland Seal Hunt, pg. 445-457. Flanker Press, St. John’s. [Contains critical notes about ice conditions between 1924 and 1941 and where harp seals were found in those years]
Sergeant, D.E. 1976. History and present status of populations of harp and hooded seals. Biological Conservation 10:95-118.
Sergeant, D.E. 1991. Harp Seals, Man and Ice. Canadian Special Publication of Fisheries and Aquatic Sciences 114. Fisheries and Oceans Canada, Ottawa.
Stenson, G.B. 2014. The status of harp and hooded seals in the North Atlantic. Report presented at the Scientific Council Meeting, June 2014. Northwest Atlantic Fisheries Organization SCR Doc. 14/026, Serial No. N6321.
Stenson, G.B., Buren, A.D. and Koen-Alonso, M. 2015. The impact of changing climate and abundance on reproduction in an ice-dependent species, the Northwest Atlantic harp seal, Pagophilus groenlandicus. ICES Journal of Marine Science 73(2):250-262. http://icesjms.oxfordjournals.org/content/73/2/250