Reposted from Polar Bear Science
Posted on March 11, 2021 |
In early February this 12 months, sea ice was a lot decrease than regular alongside the Labrador coast and nearly non-existent within the Gulf of St. Lawrence, that are two essential pupping habitats for North Atlantic harp seals. The image would have been very bleak for harp seal pups and the Davis Strait polar bears that rely on them for meals if ice hadn’t expanded and thickened by early March – but it surely did. Previous expertise means that harp seals that normally whelp within the Gulf of St. Lawrence, the place ice continues to be nicely under common this 12 months, will transfer to ice off Southern Labrador (‘the Entrance’) to have their pups.
SEA ICE OFF LABRADOR/GULF OF ST. LAWRENCE
There isn’t a strategy to sugar-coat this: there wasn’t a lot ice off the East Coast in early February, which was shaping as much as be as dangerous or worse than the current low-ice 12 months of 2011. Beneath is the weekly ‘departure from regular’ ice chart from the Canadian Ice Service for the week of Feb 1, which exhibits quite a lot of space usually lined in ice right now of 12 months (crimson) that was nonetheless open water:
Nevertheless, there was ice additional north that has now moved down the Labrador coast from Davis Strait (see under):
At 10 March, there may be nonetheless a lot much less ice than regular but it surely seems to be satisfactory on the Entrance (southern Labrador coast) for harp seals to have their pups.
Nevertheless, the pupping grounds gained’t be spreading out throughout the north coast of Newfoundland as they normally do – there merely isn’t the ice there for it:
WHEN DO HARP SEALS NEED ICE?
The timing sequence for harp seal pupping season within the North Atlantic is White Sea (late February); Gulf of St. Lawrence, aka the “Gulf” (early March, imply 5 March); Labrador/Newfoundland, aka the “Entrance” (mid to late March, imply 12 March); East Greenland round Jan Mayen Island, aka the “West Ice” (late March to early April). The Jan Mayen/West Ice area is the furthest north that harp seals pup, breed and moult.
Sea ice within the Gulf the week of eight March 2021 under just isn’t actually thick sufficient for harp seals. They want first 12 months ice (inexperienced on the chart), which is sorely missing within the Gulf this 12 months:
No distinction has been discovered between harp seals on the Gulf and people on the Entrance, so collectively they’re handled as one inhabitants for administration functions (Sergeant (1991; Stenson 2014). Harp seals are at the moment extra considerable than they’ve been for many years and are nonetheless rising. Beneath is a graph displaying adjustments in NE Atlantic harp seal numbers between 1952 and 2019 (DFO 2020):
WHAT KIND OF ICE DO HARP SEALS NEED?
In accordance with Sergeant (1991: 116) :
“…it’s attainable to categorize the kind of ice utilized by harp seals for whelping (Fig. 127). That is medium winter ice in late February with 6 to eight/10 ice cowl, i.e. it have to be sturdy sufficient however have sufficient open leads for the seals to penetrate it.” [my bold]
Sergeant (1976:98, 38) identified that ice within the Gulf is shaped in situ and normally solely will get about 40-50cm thick, whereas the ice on the Entrance is thick first 12 months ice with origins within the far north. This makes Gulf of St. Lawrence ice formation far more prone to native circumstances (heat OR chilly) and thus, the extremely variable sea ice circumstances usually are not new (Johnston et al. 2005), a truth corroborated by studies by early 20th century sealers from 1924-1941 (Ryan 2014).
Sergeant (1991: 31) made this level:
“Best year-to-year adjustments are seen within the Gulf of St. Lawrence on the southern margin of the vary, the place ice in anyone season could also be thick or virtually absent.” [my bold]
WHAT DO SEALS DO IF THERE IS LITTLE ICE?
What do harp seals do when ice circumstances are poor within the Gulf of St. Lawrence, as has occurred typically prior to now? Sergeant (1991:56) stated this:
“In 1981, with virtually no ice within the Gulf, mortality of at the very least a number of hundred younger and tens of adults was seen on the north shore seashores of Prince Edward Island….
Sergeant (1982) discovered that ice circumstances affected whelping patterns markedly within the Gulf of St. Lawrence in 1953, 1969 and 1981, or about one 12 months in ten. In 1969 at the very least, ice circumstances on the Entrance and within the Strait of Belle Isle had been gentle additionally and would have allowed grownup females which had not whelped within the Gulf to go looking northward for ice; some could have completed so.
[in 1969] There was no ice within the Gulf besides in Northumberland Strait and shore ice on the north coast of Prince Edward I. It was typically agreed that not more than 40 000 animals whelped right here… The quantity at the moment anticipated to whelp within the southern Gulf was ca. 100 000.
Most likely, the rest looked for ice, and discovering none within the northern Gulf, handed via the Strait of Belle Isle and whelped along with the Entrance herd on the coast of Labrador at Hamilton Inlet.
In 1981, nevertheless, though ice was of minimal extent and thickness within the Gulf, harp seals whelped off the west coast of the Magdalen Is. and drifted to the north coast of Prince Edward I. Right here storms destroyed the small quantity of ice and younger harp seals died because of hunger and lack of physique reserves (Dr. J.R. Geraci, in litt.).
Beneath unusually heavy ice circumstances, it isn’t attainable for harp seals to maneuver from the Entrance to the Gulf earlier than whelping, because the Strait of Belle Isle is then blocked by ice. Whelping merely happens additional south alongside the east coast of Newfoundland.” [my bold]
Nevertheless, polar bears have hardly ever penetrated into the Gulf in current heavy ice years: they stick with consuming seal pups on the ice on the ‘Entrance’ off Newfoundland and Labrador.
WHAT HAVE RECENT LOW ICE YEARS LOOKED LIKE?
The worst 12 months for low ice on the east coast in current a long time was in 2011 (Stenson et al. 2015), see under, for the week of 31 January:
Evaluating the above to this 12 months for the week of 1 Feb (under) exhibits the exceptional similarity:
Division of Fisheries and Oceans Canada (DFO) 2012. Present standing of northwest Atlantic harp seals (Pagophilus groenlandicus). Science Advisory Report 2011/070.
Division of Fisheries and Oceans Canada DFO. 2014. Standing of Northwest Atlantic harp seals, Pagophilus groenlandicus. DFO Can. Sci. Advis. Sec. Sci. Advis. Rep. 2014/011.
DFO. 2020. 2019 Standing of Northwest Atlantic Harp Seals, Pagophilus groenlandicus. DFO Can. Sci. Advis. Sec. Sci. Advis. Rep. 2020/zero20. http://www.isdm-gdsi.gc.ca/csas-sccs/purposes/Publications/result-eng.asp?params=zero&sequence=7&12 months=2020 PDF right here.
Johnston, D.W., Friedlaender, A.S., Torres, L.G., Lavigne, D.M. 2005. Variation in sea ice cowl on the east coast of Canada from 1969-2002: local weather variability and implications for harp and hooded seals. Local weather Analysis 29:209-222.
Kovacs, Okay.M. 2015. Pagophilus groenlandicus. The IUCN Crimson Listing of Threatened Species 2015: e.T41671A45231087. http://dx.doi.org/10.2305/IUCN.UK.2015-Four.RLTS.T41671A45231087.en
Ryan, S. 2014. Appendix three: Chafe’s “Notes of the Voyages” 1924-1941, In: The Final of the Ice Hunters: An Oral Historical past 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. Historical past and current standing of populations of harp and hooded seals. Organic Conservation 10:95-118.
Sergeant, D.E. 1991. Harp Seals, Man and Ice. Canadian Particular Publication of Fisheries and Aquatic Sciences 114. Fisheries and Oceans Canada, Ottawa.
Stenson, G.B. 2014. The standing of harp and hooded seals within the North Atlantic. Report introduced on the Scientific Council Assembly, June 2014. Northwest Atlantic Fisheries Group SCR Doc. 14/026, Serial No. N6321.
Stenson, G.B., Buren, A.D. and Koen-Alonso, M. 2015. The impression of fixing local weather and abundance on replica 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 material/73/2/250