Ringed seals and climate change

Ringed seals are the smallest and most abundant member of the seal family that live in the Arctic and Sub-Arctic regions. The average life span of a ringed seal is 40 years, with a diet based mainly on Arctic cod and planktonic crustaceans. Typically about 5 feet (1.5 m) long, the ringed seal is known to be solitary with their main predator being polar bears. Recently, however, the biggest predator to ringed seals has been the changing temperature in the Arctic and the detrimental changes to sea ice that follow. With declines in snowpack and sea ice due to warming ocean and atmospheric temperatures, survival has become tougher for ringed seals in the Arctic and Sub-Arctic regions. Yet ringed seals are also potentially projected to thrive due to warming, considering the early extinction of their predators. Climate change is sure to change the fate of all ringed seals in the coming years for better or worse.

General Information

Ringed seals reside within 35°N and the North Pole, and are thus known as a circumpolar based species. The effects of climate change are projected to affect both polar regions of the earth more than anywhere else. This means a changing climate and life for all those residing in these polar regions. As for ringed seals, two potential outcomes lie ahead in this ever-changing climate.

Threats

In the past decade, the Arctic region has faced some of its highest temperatures within the instrumental record. Furthermore, within the past 2000 years, summer temperature highs have never been harsher, based on paleo-climate reconstructions.[1] This warming is due to climate feedbacks mechanisms based on sea-ice melt. As sea ice melts, it frees up more open ocean water to be further heated, thus bringing about a positive feedback. Ocean water retains more heat than sea ice; additionally the albedo of sea ice is much higher than that of ocean water. Ringed seals require sea ice to live and reproduce. They live most of their lives alone, only grouping together into colonies when they are on sea ice to molt, mate, or rest.[2] Without access to sea ice, ringed seals are unable to sustain life, which further affects trophic levels both above and below. Ringed seals are both predators and prey. A predator to zooplankton and fish, the ringed seal is considered a primary consumer as well as a secondary consumer. But the tertiary consumer, or top predator, in the Arctic is the polar bear, feeding mostly on seals, including the ringed seal. Yet through further exploration, the potential fates of this Arctic food web seem to be ambiguous, leading to a very important trade off of polar bear mortality and ringed seal sustenance.[3]

Research

Most research on ringed seals is focused on their requirement of sea-ice to live and reproduce. With proposed climate change increases to occur most dramatically at the poles, the Arctic is fated to change extremely mainly with the melting of ice and changes in snowfall. Ferguson et al.[4] studied ringed seal recruitment in western Hudson Bay with a focus on six environmental variables, including: snow depth, snowfall, rainfall, the temperature when pups were born, North Atlantic Oscillation (NAO) mechanisms, and lastly the spring break-up. The results of Ferguson et al. determined that decreases in snowfall had a negative effect on ringed seal recruitment, most likely from the occurrence of earlier break up of sea ice. The main process driving this break up is albedo, with less snowfall and more ocean exposed the ice melts more quickly. With seal pups being forced into the water sooner due to lack of ice, recruitment numbers drops and result in a downward trend of the population. Ringed seals are not the only animals that require sea-ice in the Arctic and Sub-Arctic to thrive. Trophic levels come into play in terms of the food web and the reliance of one population on another or many others for survival. Most of this research is actually studied through simulations, since this requires future projections and interactions between many population, physical ocean, and biological mechanisms. Meier et al.[5] studied current and future projections of climate in regards to sea-ice in the Baltic Sea by means of atmosphere-ocean models. Firstly, the ringed seal relies on sea-ice for breeding and is unable to breed on land, meaning, as ice melts away in the future, breeding grounds will become much scarcer. It was determined that only one bay, Bothnia Bay in the Baltic Sea, will be able to be used by ringed seals for breeding, vastly limiting their options. It was further determined that ringed seals are only able to be successful with strained conditions in areas of 90%-100% ice cover probability. (Meier et al. 2004) The changes in ice scarcity projected for the future seem to greatly hinder th ability for ringed seals to reproduce in the Baltic Sea. Interestingly, Hoover et al.[3] looked at multiple marine populations in the Hudson Bay while factoring in both simulated current and higher harvest rates, ultimately determining that ringed seals are identified to increase in population. This is mostly due to the decrease in polar bear populations, the main predator to the ringed seal. Even with a doubling of harvest rates and under the high (A1B) climate scenario, the ringed seals were determined to thrive even more. Hoover et al. further determined that the ringed seal’s large presence as a circumpolar population along with unspecialized feeding makes the ringed seal less sensitive compared with other Arctic land and marine species. One of the final general conclusions made by Hoover et al. stated that while many current harvested populations will decrease with proposed climate change, ringed seals should be considered for redirecting harvest towards their populations.

In Context

The ringed seal is a very important link in the food chain, separating primary producers from primary predators. Historically the ringed seal was the most abundant of any other seals in the Arctic, yet this species has had its share of population slumps. First there was over-harvesting of the ringed seal, drastically dropping numbers from about 200,000 in 1900 to only 4,000 in the 1970s. Secondly, pollution from organocholrides due to DDT and other residues caused many Arctic marine mammals including the ringed seal to become sterile. Sterility still affects many marine mammals living in the Arctic, being a mechanism of bioaccumulation within the Arctic food web.[5] The ringed seal is not fragile considering their past, yet climate change will have the greatest population effect on the ringed seals thus far due to anthropogenic causes.

Future

The future of ringed seal populations in the Arctic and Sub Arctic is uncertain, but two main projections surface based around habitat and predators. The first projection focuses on the direct effects of climate change on sea-ice and the limited environment that it will provide the ringed seal with. The majority of past research has been focused around this main idea of quicker melting sea ice leading to lower ringed seal populations from lack of breeding areas. Yet what most research has not also taken into account is the quick drop in polar bear populations. As the main predator to ringed seals, the polar bear’s extinction in the coming years will allow for ringed seal populations to flourish. In the end, ringed seals are estimated to thrive with no polar bears present in the Arctic and Sub Arctic.[3] Although this predator factor is involved with more recent research, it does not necessarily mean this will be the outcome, considering the uncertainty in such projections. Overall, ringed seals populations will fluctuate regardless of each potential outcome and climate change is certain to affect not only the ringed seal but all Arctic and Sub Arctic animal populations.

References

  1. ↑ Olsen, M. S.; Callaghan, T. V.; Reist, J. D.; Reiersen, L. O.; Dahl-Jensen, D.; Granskog, M. A.; Goodison, B.; Hovelsrud, G. K.; Johansson, M.; Kallenborn, R.; Key, J.; Klepikov, A.; Meier, W.; Overland, J. E.; Prowse, T. D.; Sharp, M.; Vincent, W. F.; Walsh, J. (2011). "The changing arctic cryosphere and likely consequences: An overview". AMBIO: A Journal of the Human Environment. 40 (sp1): 111–118. doi:10.1007/s13280-011-0220-y.
  2. ↑ Ringed seal - phoca hispida . (2013). Retrieved from http://animals.nationalgeographic.com/animals/mammals/ringed-seal/
  3. 1 2 3 Hoover, C (2013). "Effects of hunting, fishing and climate change on the Hudson bay marine ecosystem: Ii. Ecosystem model future projections". Ecological Modeling. 264: 143–156. doi:10.1016/j.ecolmodel.2013.01.010.
  4. ↑ Ferguson, S. H.; Stirling, I.; McLoughlin, P. (2005). "CLIMATE CHANGE AND RINGED SEAL (PHOCA HISPIDA) RECRUITMENT IN WESTERN HUDSON BAY". Marine Mammal Science. 21: 121–135. doi:10.1111/j.1748-7692.2005.tb01212.x.
  5. 1 2 Meier (2004). "Simulated distributions of baltic sea-ice in warming climate and consequences for the winter habitat of the Baltic ringed seal". AMBIO: A Journal of the Human Environment. 33 (4): 249–256. doi:10.1579/0044-7447-33.4.249.
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