Melting Moves Marine Mammals

Reference: Hamilton, C.D., Vacquié-Garcia, J., Kovacs, K.M., Ims, R.A., Kohler, J., and Lydersen, C. (2019). Contrasting changes in space use induced by climate change in two Arctic marine mammal species. Biology Letters. 15:20180834, 1-4. https://royalsocietypublishing.org/doi/10.1098/rsbl.2018.0834

The Problem

Climate change is already impacting species globally, and Arctic species are especially threatened. As glaciers retreat and sea-ice declines in the Arctic, the species that live there are losing their habitat. Among those particularly at risk are marine mammals found nowhere else in the world. For long-lived species such as the ringed seal (Pusa hespida) and the white whale (Delphinapterus leucas), changes in habitat could mean life or death. To survive, these species must find some way to adapt.

In Svalbard, Norway, sea-ice along the coastline declined dramatically in 2006. Historic movement data gleaned from studies of the ringed seal and white whale shows that both species spent around half of their time along the edge of glaciers prior to the sea-ice decline. Because movement data exists from before the decline, the abrupt decrease in sea-ice presented researchers with an opportunity to study how both species of marine mammals responded to the change in their environment.

The ringed seal in this photo may appear care-free, but this Arctic species could be at risk due to its difficulty adapting to rapidly changing environmental conditions. Source: https://commons.wikimedia.org

The Approach

To gain information on animal movement, 28 ringed seals and 16 white whales were equipped with biotelemetry devices (used to record animal movement remotely and wirelessly) between 2010 and 2016. This data was compared with the historic movement data from 1995-2003. Researchers then used this information to determine whether there was a difference in the amount of time the species spent within 5 kilometers (a little over 3 miles) of the tidal glaciers.

The Outcomes

Ringed seals and white whales responded very differently to reductions in sea ice. White whales spent significantly less time near the glacier fronts and instead broadened their home ranges, spending more time in the middle of fjords. Ringed seals, however, stayed close to the remaining glacier fronts and spent even more time in glacial refugia. The seals’ home range was thus reduced following the decline in sea ice. Changes in sea ice have also affected these species’ diets. In the past, both species’ chiefly fed on polar cod. Now, however, white whales have shifted to feeding on prey species that have moved into the Arctic from the Atlantic Ocean while ringed seals continue to feed primarily on cod.

A white whale and her calf. Though it is an endangered species, the white whale appears to be adapting relatively well to changes in sea ice by shifting its range and feeding on new, more abundant, prey species. Source: https://commons.wikimedia.org/

What this means for these species

This study provides us with a stark contrast. White whales show flexibility in their behavior that will likely improve their ability to adapt to climate change. Ringed seals, on the other hand, show a strict retreat into the remaining available habitat and stay dependent on the same, ever scarcer, prey. When organisms are flexible in their feeding habits and behavior, like the white whale appears to be, they can often cope with changes in the environment more easily than more specialized species, like the ringed seal. As the impacts of climate change are increasingly felt, species unable to adapt are likely to decline, possibly to the point of extinction. Understanding the responses of species to climate change can help us to predict how ecosystems and individual species will respond in the future.

You can learn more and make a difference

If you want to learn more about how we know that climate change is happening, its causes, effects, and some proposed solutions, check out this page from NASA: https://climate.nasa.gov/evidence/. You can make a difference by taking little steps to decrease carbon emissions. If you would like to calculate your carbon footprint and learn some practical ways to offset it, head over to Carbon Footprint: https://www.carbonfootprint.com/.

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