From polar bear science
Posted on Jan 7, 2021 |
The NOAA 2020 Arctic Report Card not only summarizes the changes in sea ice, but also contains two reports that document the greatest benefit of much less summer sea ice than before 2003: Increased primary productivity. Polar bears, which are at the top of the Arctic food chain, have benefited from this phenomenon as the Arctic marine mammals they rely on for food – seals, walruses and bowhead whales – thrive in the summer despite less ice.
In the chapter on sea ice (Perovich et al. 2020), my favorite among all published figures is the chart of sea ice from September versus March (above). As you can see, ice extent has been practically flat in March since 2004 (no declining trend). As the following graphic shows, the expansion in September has not shown any trend since 2007, as NSIDC ice expert Walt Meier showed last year (see below). : It doesn’t take much imagination to see that the value for 2020 from the graph above (the second lowest after 2012) has not changed the flat trend line.
The chapter also included this comparison of the March and September ice maps:
The real eye-opener in the report, however, is the admission that much less summer ice has benefited overall Arctic food change due to increased primary productivity.
BENEFITS OF LESS SUMMARY OF ICE
One of the highlights highlighted in the report is this gem:
In July and August 2020, the regional primary productivity of the oceans in the Laptev Sea was ~ 2 times higher in July and ~ 6 times higher in August than the respective monthly average.
It’s nice to see that the longer ice-free seasons we’ve seen since 2007 have an advantage. In fact, less summer ice has been a net benefit for most animals in the Arctic and peripheral seas, as less ice and more sunlight increase “primary productivity” in most areas. Primary productivity refers to phytoplankton, those unicellular plants that form the basis of life in the ocean because they convert sunlight into stored energy: sunlight is their food. Longer ice-free seasons – with less ice and more sunlight – create the conditions for exponential growth of phytoplankton and produce “blooms” that can be seen by satellites. One such bloom can be seen below in the Barents Sea on July 26, 2020 (NOAA photo).
In the table below from a group of NOAA authors (Frey et al. 2020), primary productivity has increased in almost all regions of the Arctic since 2003, without data from 2020:
Similar results are discussed in a government report from Canada (Coupel et al. 2019), which summarizes reports of recent increases in phytoplankton in the Arctic. I revamped a graphic I posted earlier this year to show how this works (see below). Higher primary productivity due to a longer ice-free period benefits the entire Arctic food chain, in which polar bears occupy the top spot: thicker seals due to more food mean thicker polar bears with improved survival.
Abundant phytoplankton → more food for single-celled animals (zooplankton), fish and invertebrates living on the ground such as mussels → productive reproduction of krill, fish and mussels (population growth); more fish in turn → thicker ringed seals and bearded seals, which feed mainly in the ice-free season, and thus fat female seals → more fat puppies in the following spring (Crawford et al. 2015) for polar bears when they need them most. Unless other factors come into play that reduce the availability of prey, such as: B. too much ice or snow over ice in spring (Crockford 2015, 2017), polar bears tend to be thicker, healthier and reproduce more successfully, which at least leads to a stable effect. if not growing population numbers – as we have seen since 2005 in the Barents and Chukchi Seas and in the Gulf of Boothia (Aars 2018; Dyck et al. 2020; Lippold et al. 2019; Regehr et al. 2018; Rode et al . 2014, 2018).
In addition to ringed seals, bearded seals and polar bears, bowhead whales (see below) have also benefited from this increased primary productivity, as explained in another chapter of the Arctic Report Card by John George and colleagues.
These authors (George et al. 2020) stated in their chapter on bowhead whales (see range map from their article below):
The population size of the nose heads in the Pacific Arctic has increased over the past 30 years, likely due to the increase in primary production of the oceans as well as the movement north of the zooplankton they feed on.
In addition, I suspect that the Pacific walrus’ large population size and health are recent indicators that it is a different species that has benefited from less summer sea ice (Crockford 2014a, b). Walruses feed on vertebrates living in vertebrae, whose population size would be increased by abundant plankton, allowing more walruses to eat without running out of food, as was known in the past during what are known as boom-and-bust population cycles (Fischbach et al. 2016; Lowry 1985; MacCracken et al. 2017).
REFERENCES
Aars, J. 2018. Polar bear population changes: protected, but quickly lost to habitat. Fram Forum Newsletter 2018. Fram Center, Tromsø. Download PDF here (32 mb).
Coupel, P., Michel, C. and Devred, E. 2019. Case Study: The Ocean in Bloom. In the Arctic Sea of Canada, A. Niemi, S. Ferguson, K. Hedges, H. Melling, C. Michel et al. 2019. Canadian Technical Report Fisheries and Water Sciences 3344.
Crawford, JA, Quakenbush, LT and Citta, JJ 2015. A comparison of the diet, condition, and productivity of ringed and bearded seals between historical (1975–1984) and recent (2003–2012) periods in the Bering and Chukchi Seas of Alaska. Advances in Oceanography 136: 133-150.
Crockford, SJ 2014a. On the beach: Walrus transports are nothing new. Briefing Paper of the Global Warming Policy Foundation 11. PDF here.
Crockford, SJ 2014bThe walrus excitement: Walrus transports are nothing new. Http://www.thegwpf.org/gwpftv/?tubepress_item=cwaAwsS2OOY&tubepress_page=2
Crockford, SJ 2015. The Arctic Fallacy: Sea Ice Stability and the Polar Bear. Global Warming Policy Foundation Briefing Paper 16. London. Available at http://www.thegwpf.org/susan-crockford-the-arctic-fallacy-2/
Crockford, SJ 2017. Testing the hypothesis that routine sea ice cover of 3-5 mkm2 leads to a decrease in the population size of polar bears (Ursus maritimus) by more than 30%. PeerJ Preprints January 19, 2017. Doi: 10.7287 / peerj.preprints.2737v1 Open Access. https://peerj.com/preprints/2737/
Dyck, M., Regehr, EV and Ware, JV 2020. Assessment of the frequency of the polar bear subpopulation in the Gulf of Boothia using genetic marrow recapture. Final report, Government of Nunavut, Ministry of Environment, Iglulik. June 12, 2020. Pdf here.
Fischbach, AS, Kochnev, AA, Garlich-Miller, JL and Jay, CV 2016. Pacific Walrus Coastal Haulout Database, 1852–2016 – Background Report: US Geological Survey Open-File Report 2016–1108. http://dx.doi.org/10.3133/ofr20161108. The online database can be found here.
Frey, KE, Comiso, JC, Cooper, LW, Grebmeier, JM and Stock, LV 2020. Primary productivity of the Arctic Ocean: The response of marine algae to global warming and the decline in sea ice. Report on the Arctic 2020. NOAA. DOI: 10.25923 / vtdn-2198 https://arctic.noaa.gov/Report-Card/Report-Card-2020/ArtMID/7975/ArticleID/900/Arctic-Ocean-Primary-Productivity-The-Response-of-Marine -Algae-to-climate-warming-and-sea-ice-decline
George, JC, Moore, SE and Thewissen, JGM 2020. Bowhead Whales: Current Insights into their Biology, Status and Resilience. 2020 Arctic Report, NOAA. DOI: 10.25923 / cppm-n265 https://arctic.noaa.gov/Report-Card/Report-Card-2020/ArtMID/7975/ArticleID/905/Bowhead-Whales-Recent-Insights-into-Their-Biology-Status -and-resilience
Lippold, A., Bourgeon, S., Aars, J., Andersen, M., Polder, A., Lyche, JL, Bytingsvik, J., Jenssen, BM, Derocher, AE, Welker, JM and Routti, H. 2019. Trends in persistent organic pollutants over time in Barents Sea polar bears (Ursus maritimus) in relation to changes in eating habits and body condition. Environmental Science and Technology 53 (2): 984- 995.
Lowry, L. 1985. “Pacific Walrus – Boom or Bust?” Alaska Fish & Game Magazine July / August: 2-5. pdf here.
MacCracken, JG, Beatty, WS, Garlich-Miller, JL, Kissling, ML and Snyder, JA 2017. Final Species Status Assessment for the Pacific Walrus (Odobenus rosmarus divergens), May 2017 (Version 1.0). US Fish & Wildlife Service, Anchorage, AK. PDF here (8.6 mb).
Perovich, D., Meier, W., Tschudi, M., Hendricks, S., Petty, AA, Divine, D., Farrell, S., Gerland, S., Haas, C., Kaleschke, L., Pavlova O., Ricker, R., Tian-Kunze, X., Webster, M. and Wood, K. 2020. Sea ice. 2020 Arctic Report, NOAA. https://arctic.noaa.gov/Report-Card/Report-Card-2020/ArtMID/7975/ArticleID/891/Sea-Ice PDF of the entire Arctic Report Card here (12 MB).
Regehr, EV, Hostetter, NJ, Wilson, RR, Rode, KD, St. Martin, M., Converse, SJ 2018. The integrated population modeling provides the first empirical estimates of the vital rates and the frequency of polar bears in the Chukchi Sea. Scientific reports 8 (1) DOI: 10.1038 / s41598-018-34824-7 https://www.nature.com/articles/s41598-018-34824-7
Rode, KD, Regehr, EV, Douglas, D., Durner, G., Derocher, AE, Thiemann, GW and Budge, S. 2014. Variation in a top arctic predator’s response to habitat loss: feeding and reproductive ecology of two polar bear populations. Global Change Biology 20 (1):76-88. http://onlinelibrary.wiley.com/doi/10.1111/gcb.12339/abstract
Rode, KD, RR Wilson, DC Douglas, V. Mühlenbruch, TC Atwood, EV Regehr, ES Richardson, NW Pilfold, AE Derocher, GM Durner, I. Stirling, SC Amstrup, MS Martin, AM Pagano and K. Simac. 2018. The fasting behavior in spring in a predator with a marine tip provides an index for the productivity of the ecosystem. Global Change Biology http://onlinelibrary.wiley.com/doi/10.1111/gcb.13933/full
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