The report on the latest population estimate for harp seals off the east coast of North America was released in late March without fanfare and therefore no media attention. This was one of the missing scientific reports mentioned in my State of the Polar Bear Report 2019 released in February (Crockford 2020): results of surveys promised for months or years by early 2020 but not delivered.
Not surprisingly then, we find the report has good news: the population estimate of harp seals in the NW Atlantic has risen to about 7.6 million (range 6.55-8.82) animals (DFO 2020), up from 7.4 million in 2014 (DFO 2014).
Note that the survey was done in March 2017, a low ice year for the Gulf of St. Lawrence (see discussion below) and while this may have resulted in some increased mortality for pups born there, it is also known that many ‘Gulf’ pregnant females will instead have given birth off Newfoundland and Labrador in a whelping region called ‘The Front’. Apparently, these factors were accounted for in the population model.
Harp seal pups born at the Front are an important food for Davis Strait polar bears. This increase in the prey base for Davis Strait polar bears suggests the bear population may have grown substantially since the last survey in 2007 (Peacock et al. 2013; Rode et al. 2012). Davis Strai is the only subpopulation of polar bears officially considered to have ‘likely increased’ at 2018 by Environment Canada. A new Davis Strait population size survey was apparently completed in 2018 but the results are not yet available (Crockford 2020).
Highlights, quotes, and figures from the harp seal report below. Continue reading
A just-released report on the most recent (2016) survey shows Western Hudson Bay polar bear numbers were still stable despite predictions that this subpopulation would be wiped out completely (reduced to zero) due to low Arctic sea ice.
The authors of the report on the August 2016 aerial survey of the Western Hudson Bay polar bear subpopulation (Dyck et al. 2017) state clearly that the only trends they could find were that the number of adult males increased somewhat over 2011 estimates and the number of females either declined or remained stable. The overall population estimate was a bit lower (11% less) compared to the 2011 survey but the difference is not statistically significant. Therefore, the population status must be stable.
2011 estimate: 949 bears (using comparable data, range 618-1280), litter size 1.43
2016 estimate: 842 bears (using comparable data, range 562-1121), litter size 1.63
[cf. Foxe Basin [stable], from 2009-2010 survey (Stapleton et al. 2016) litter size was 1.54]
An 11% decline in WH numbers since 2011 is most definitely NOT the decline to ZERO (extirpation) we were told to expect with Arctic sea ice as low as it has been since 2007 (Crockford 2017, see list of annual minimum extents 2007-2017 here).
Note: The percentage decline from 2011 to 2016 for Western Hudson Bay polar bears is 11%, NOT 18% as claimed recently by Andrew Derocher on twitter: it is not appropriate to compare the official 2011 estimate of 1030 (Stapleton 2014) to the 2016 estimate of 842 because the methods used to generate the estimates were different (Dyck et al. 2017). The authors of the report state that the estimate for 2011 that’s comparable to 2016 is 949.
An 11% decline from 1030 would be 917 bears, a statistically insignificant decline that is also biologically insignificant and therefore, so slight as to indicate a stable population.
Predicted sea ice at 2050 and 2080 shown below (see Crockford 2017 for details):
Quotes, map, and table from the Dyck et al. 2017 report (pdf here) are copied below.
Posted in Conservation Status, Population, Sea ice habitat
Tagged decline, Derocher, estimate, extirpated, facts, increasing, polar bear, population, significant, size, slight, stable, statistics, status, survey, western hudson bay
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