Harp seal population critical to Davis Strait polar bears is still increasing

New report: Harp seal population critical to Davis Strait polar bears is still increasing

From Polar Bear Science

Posted on May 14, 2020 | Comments Off on New report: Harp seal population critical to Davis Strait polar bears is still increasing

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.

Harp seal on ice around PEI _DFO 2017

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).

Harp seal pup_DFO Newfoundland

Highlights, quotes, and figures from the harp seal report below.

Ice conditions in March 2017

As you can see below, at 24 March 2017 when harp seal pups in the Gulf of St. Lawrence would have been about 1 week old and their mothers still with them most of the time nursing and a likely time for a survey. There was little preferred ice (thin first year ice, ca. 50cm thick, light green) around Prince Edward Island in the south and towards the Strait of Belle Isle in the north and none around the Magdalen Islands in the centre where pupping is usually concentrated:

Sea ice Gulf March 24_2017_CIS

A good ice year (2015) in the Gulf, same date in March, had much more suitable whelping habitat for harp seals, including around the Magdalen Islands (see below), and there was also abundant ice at the Front:

Sea ice Gulf March 24_2015_CIS

In contrast, there was ample suitable ice for whelping harp seals at the end of March at the Front in 2017, although there have been better years than this. Oddly enough, 2017 was the year that southern Labrador and northern Newfoundland were ‘crawling with polar bears‘ from early April and by the end of April, the ice off Newfoundland was the thickest it had been since 2007.

East Coast 2017 Stage of development Weekly_March 27

QUOTES FROM THE REPORT [my bold]:

Harp seal range DFO_accessed 16 April 2015

Highlights

-The model indicates that the population increased from the 1970s until the mid-1990s. Between the mid-1990s and 2011 the population was relatively stable. Since then it is estimated that the population has begun to increase likely due to reductions in the removals and high reproductive rates [Figure 8, below].

-The model estimated pup production in 2019 is 1.4 (95% CI, 1.23-1.49) million and a total population size of 7.6 (95% CI, 6.55-8.82) million.

Harp seal population size NW_1952-2019_DFO March 2020 Fig 8

Assessment

The number of Harp Seal pups born in a year is estimated periodically from surveys flown in the spring when the seals gather on the ice to have their pups. Estimates of total population size are based on a population model that fits to estimates of pup production and reproductive rates and incorporates information on annual catches in Canada and Greenland, by-catch, struck and lost, and unusual pup mortality due to poor ice conditions. A long-term environmental index is used to indicate changes in the environment that impact reproductive rates and juvenile survival.

Photographic and visual aerial surveys were flown in the Gulf of St. Lawrence, and off Newfoundland, to determine Harp Seal pup production during March 2017. Estimated pup production in the southern Gulf was 18,300 (95% CI, 15,400-21,200) seals; 13,600 (95% CI, 7,700-19,500) in the northern Gulf and 714,600 (95% CI, 538,800-890,400) at the Front, for a total estimated pup production in 2017 of 746,500 (95% CI, 570,300-922,700) (Table 2). This estimate is approximately one half of the number of pups estimated in 2008, but similar to estimates from 1999, 2004 and 2012. Overall, the proportion of pups born in the southern Gulf of St Lawrence has declined from a high of 28% in 1994 to 2% in 2017 (Table 2).

Since the 1950s, reproductive rates have shown a declining trend while inter-annual variability has increased (Fig. 4). These highly variable reproductive rates have continued although the very low rates observed in 2010 and 2011 have not occurred again. Relatively high reproductive rates were observed in 2014 and 2015 associated with a period of extensive ice coverage and high capelin abundance (the main prey of Harp Seals) and have remained relatively high for the past five years. The longer-term decline in reproductive rates is a reflection of density-dependent processes associated with increased population size. The large inter-annual variability is due to varying rates of late term abortions which appear to be related to changes in capelin abundance, and mid-winter ice coverage (which reflects environmental conditions that influence a variety of species).

The Northwest Atlantic Harp Seal population has increased significantly over the past five decades. The general decline in reproductive rates over this period, as well as a decline in size at age suggests that the population is approaching its environmental carrying capacity (K). These density dependent changes are affecting the dynamics of this population although it is very difficult to determine the exact relationship between the current population and the carrying-capacity.

Sources of Uncertainty

Although reduced ice cover and quality are known to result in increased YOY mortality, the nature of that relationship is not known. It is also not known how ice cover and quality will change in the future. Nevertheless, as further reductions in ice coverage are predicted, poor ice conditions are likely to have an increased impact on YOY mortality. Reduced ice cover may also affect food availability and body condition of Harp Seals which, in turn, could impact reproductive rates. Again, the nature of these relationships is poorly understood and thus difficult to account for in the population assessment

See the full DFO report here.

References

Crockford, S.J. 2020. State of the Polar Bear Report 2019. Global Warming Policy Foundation Report 39, London. PDF here.

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.

DFO. 2014. Status of Northwest Atlantic harp seals, Pagophilus groenlandicus. DFO Can. Sci. Advis. Sec. Sci. Advis. Rep. 2014/011. PDF here.

Peacock, E., Taylor, M.K., Laake, J., and Stirling, I. 2013. Population ecology of polar bears in Davis Strait, Canada and Greenland. Journal of Wildlife Management 77:463–476. http://onlinelibrary.wiley.com/doi/10.1002/jwmg.489/abstract?deniedAccessCustomisedMessage=&userIsAuthenticated=false

Rode, K.D., Peacock, E., Taylor, M., Stirling, I., Born, E.W., Laidre, K.L., and Wiig, Ø. 2012. A tale of two polar bear populations: ice habitat, harvest, and body condition. Population Ecology 54:3-18. http://link.springer.com/article/10.1007/s10144-011-0299-9

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19 thoughts on “Harp seal population critical to Davis Strait polar bears is still increasing

  1. Oh my God!…There’ll be so many of them that they’ll gang up on the polar bears and give them a damned good thumping.

    Is there no mercy in this world?

    • Actually, if the seals are that endangered, and those non-vegan polar bears are responsible, some greenie weenies need to step up, get up there, and give those denialist bears a good talking to. Preferably nose to nose.

    • Actually, if the seals are that endangered and those non-vegan polar bears are responsible, some greenie weenies need to step up, get up there, and nose to nose, tell them off! That should go down well.

  2. Good posting by Charles of a good update report by Dr. Crockford. Looks like the polar bear was nominated as an “indicator species” by the CAGW crowd, and it turns out the news of their demise was somewhat premature. How can a seal population survey be completed in 2018 and not yet available? That seems to require deliberate misconduct. Imagine my surprise. Stay sane and safe.

    • “indicator species” , oh you mean the “canary in the coal mine” meme.

      Now the whole point of having a canary in the coal mine is that you keep a very close eye on it to see if it changes colour or falls dead in the bottom of the cage. The last published survey was done in 2007 !

      We can be sure if the canary had turned white of fallen off its perch we would have heard a whole lot more about it.

      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).

      Many thanks to Dr Crockford for leaking these bits of MSM-banned information.

      So they grudgingly accept this population ‘likely increased’ but won’t release the survey. I guess they are still working on “homogenising” the data to fit their population models.

  3. So, basically, with over 7 million estimated harp seals in 2014 they were screeching that harp seals were going extinct. And they honestly do not understand why no one believes anything they say?

  4. I want to buy a disused ‘protest’ polar bear suit as it’s jolly cold for the time of year here in UK.

  5. Here’s a theory completely unbacked by any data.

    Seal hunting (by humans) has become unpopular to say the least. The resulting increase in the seal population has led to the collapse in the cod fishery. However it has allowed the increase in polar bear numbers.

    Therefore seal hunting (by humans) threatened the survival of polar bears. Of course, that ignores the hunting of polar bears by humans which, in this case, is a lurking variable.

    • As I understand it, polar bear declines 30-50 years ago were due to completely unregulated human hunting of all sorts. Maybe much thicker ice from the cold 60’s/70’s had things temporally out of balance for the bears/seals hunting relationship as well? I just can’t see really thick multi year ice as helpful to anything except albedo.

      The collapse of the Cod fishery was over fishing by everyone off the Grand Banks in Nfld. (including the seals) and Spanish fishing fleets that Canada finally confronted in the 1990’s at the time of the collapse. Slowly, the cod are coming back, the seals are doing exceptionally fine and dining on the fishery, and the polar bears are doing so swimmingly well, that they too are again multiplying, enough to becoming a problem for many remote communities in the North and parts of the south like Nfld/Labrador and Churchill just because there is no shortage of bears everywhere and they are expanding their ranges and territories.

      Since the seals aren’t hunted as much anymore by anyone, especially in the south and including indigenous folk as the fur markets were destroyed by Greenpeace and the animal rightists, it would appear there is an overabundance of seals, that are a stressor on the recovery of the fishery. The poor fish are getting it from everyone, including the fat polar bears that are moving south where there is an abundance of seals. And around and round we go. Don’t worry…be Happy.

    • There is a mass of cod literature, but often not mentioned for are physical changes evident as far back as the 90s. Was just discussing with friends the decrease in crab populations in the northern Gulf of Mexico (freshwater dependent) coincident with the increases in two of their main predators, Ridley sea turtles and red drum, both partly due to restrictive regulations. A paper in North Carolina not long ago came out with the problem of loggerheads tearing up crab traps. “Eighty seven percent of pots were damaged throughout the course of the study, and gear damage peaked in late June to early July. We measured a 40% reduction in blue crab catch in crab pots that were damaged. Loggerhead sea turtle sightings were consistent with areas of high gear damage.”

      The not unreasonable idea of total ecosystem management is turning out to be more of an education, in part because the goal is often preservation of an imagined necessary outcome.

        • 2hotel9
          You go first, some got runoff by suggesting just keeping current levels for the fish which were abundant enough, not so about the turtles at the time. Recent paper speculated that shrimp regulations were reducing the bycatch that the much more common ridleys may need now. Like pelicans maybe they turn into beggars, easier than diving. Can’t just do one thing, can’t have all species at maximum possible populations at all times, especially when they eat each other. Modelers apparently don’t take ecology courses.

          • I remember the good ole’ days, snagging crabs with string baskets off the bridges along old Highway 11 and off the old Bay Saint Louis bridge, along the back street bridges in Biloxi and Pascagoula. And yes, I do know where Bayou La Batre, had an aunt and uncle lived down in Coden, AL.

  6. So instead of being dispatched with a single shot by human hunters, more harp seal pups get to spend their last seconds in terror being torn apart by a polar bear.
    How humane.

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