Previously, I highlighted new research results that showed, contrary to expectations, polar bears in the Chukchi Sea subpopulation are doing better – despite declines in extent of September sea ice – since the 1970s. So it might not come as much of a surprise to find that the same is true for the primary prey of polar bears in the Chukchi and Bering Seas, Arctic ringed seals (Phoca hispida hispida).
Surprisingly, less than 6 months after Arctic ringed seals were placed on the American list of “threatened” species (under the ESA, see previous post here), actual research in Alaska has shown that declines in sea ice have proven better for ringed seals, not worse.
At a presentation given at the Lowell Wakefield Fisheries Symposium in March (Anchorage, Alaska) [program and links to pdfs here] Justin Crawford, a biologist with the Alaska Department of Fish and Game (ADF&G) presented the results of ringed seal research conducted by himself and fellow ADF&G biologist Lori Quakenbush in the Chukchi and Bering Seas (posted online by the event organizers, see references below).
As for polar bears, the Crawford and Quakenbush presentation provides some very interesting details on the status of Chukchi and Bering Sea ringed seals over the last 40 years, and contains some mighty “inconvenient” conclusions that should raise some eyebrows.
I’ve summarized these details and conclusions below in point form, with a map.
Figure 1. Crawford and Quakenbush 2013 study area in the Chukchi and Bering Seas. (marked in dark pink). Map from Kelly et al. 2010, modified. Click to enlarge.
Presentation summary (direct quotes are from the presentation text):
- It has been predicted that “changes in Arctic sea ice” and “ocean warming” due to anthropogenic global warming (“climate change” in their lexicon) will harm Arctic seals by: “reducing habitat (diminished sea ice and snow); alter food webs & energy transfer; disease transmission.” They don’t specify in the text how they were measuring sea ice changes but I presume they mean the minimum extent in September (as was the case for the polar bear study).
- They sampled ringed seals for: age, body condition (relative fatness), growth (body length), “reproductive productivity” (pregnancy rates, age at first pregnancy), diet (stomach contents), blood (for indications of disease).
- They sampled about 5,000 seals in the 1970s (“the past”) and more than 1,000 between 1998 and 2010 (“now”) in the Chukchi Sea and northern Bering Sea (which corresponds to the “Chukchi Sea” subpopulation of polar bears).
- They found that body condition has been stable since the 1970s; seals are growing faster now than in the past and pup survival has improved over time, despite the fact that “sea ice and snow conditions are changing.”
- They found that, contrary to predictions, while ringed seal diet has change over time, body condition of both pups and adults did not change.
- They found that, contrary to predictions, seals now “reach sexual maturity at younger age now than in the past.”
- They found antibodies to known diseases (in the blood), contrary to predictions, were below or similar to levels found in the past.
Their conclusions (as for polar bears of this region) run strongly counter to predictions (my comments are in square brackets):
- “Overall, our biomonitoring data suggest that current conditions are more favorable for ringed seals than those in the past.”
[In other words, contrary to predictions, less ice is better for ringed seals.]
- This might be explained by “a lag time before ringed seals exhibit symptoms”
[In other words, their assumption of an immediate response to declining sea ice and snow may be wrong – it may take much longer than they supposed to see the effects they expect.]
- Or, it might be that “seals may be more resilient than predicted.”
[In other words, ringed seals might easily adapt to changes in sea ice, contrary to expectations.]
- “Arctic marine ecosystem’s response to change is difficult to predict” due to “interannual variability” and “regional differences.”
[In other words, it looks like “the Arctic” might not be a biologically significant region in terms of climate change – that regional differences within the Arctic may be so dissimilar that pan-Arctic predictions are meaningless.]
Apparently, the authors did not consider another possibility: that reductions in the amount of sea ice remaining in September might be beneficial to ringed seals.
After all, in contrast to polar bears, the open-water season is when ringed seals do most of their feeding and a longer open-water season gives them longer to put on fat for the coming winter. Similar to polar bears, it appears that the amount of sea ice cover during late winter through early summer (February to June) is what is critical for ringed seals (see previous posts here, here, and here.
And while the sea ice cover in September in the Chukchi Sea may have declined since the 1970s, the maximum amount of ice in the Bering Sea (usually reached in May each year) has been much higher over the last 10 years than it was in 1979 (see previous post here). In 2012, the previous high record was exceeded by a huge amount and 2013 was not far behind (see maps here).
Is it really any wonder that ringed seals and polar bears in the Chukchi and Bering Seas are doing so well?
References
Crawford, J. and Quakenbush, L. 2013. Ringed seals and climate change: early predictions versus recent observations in Alaska. Oral presentation by Justin Crawfort, 28th Lowell Wakefield Fisheries Symposium, March 26-29. Anchorage, AK. Abstract below, find pdf here:http://seagrant.uaf.edu/conferences/2013/wakefield-arctic-ecosystems/program.php
Kelly, B. P., Bengtson, J. L., Boveng, P. L., Cameron, M. F., Dahle, S. P., Jansen, J. K., Logerwell, E. A., Overland, J. E., Sabine, C. L., Waring, G. T. and Wilder, J. M. 2010. Status review of the ringed seal (Phoca hispida). NOAA Technical Memorandum NMFS-AFSC-212.
www.afsc.noaa.gov/Publications/AFSC-TM/NOAA-TM-AFSC-212.pdf
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