Climate change

Consequences for whales?

Climate change represents a real and measured phenomenon. Average air and water temperatures have changed in many regions, important ocean currents have been altered, the Arctic and Antarctic are melting at alarming rates and the acidification of waters is sometimes making them unsuitable for life. Although the consequences of climate change on the marine environment are undeniable, the repercussions on whales are still unknown. However, scientists expect that climate change will impact the giants indirectly: by modifying their habitat and affecting their food resources.

Mixing it up!

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  • Photo credit : © GREMM

Marine currents are at the basis of the entire food network; they allow mixing of water layers and thus a recirculation of nutrients conducive to the growth of microscopic algae. They can also contribute to creating favourable conditions for the accumulation of animal plankton and fish in certain zones such as upwellings and polynyas (ice-free polar zones). These food-rich zones often represent critical habitats for cetaceans. Water temperature, salinity and wind are some of the factors governing the great ocean currents as well as local currents and will most certainly be altered by climate change. These changes might modify whales’ habitat substantially and affect their food resources, like the rivers inhabited by certain dolphins and threatened by rising salinity levels and sediment volumes.

For example, the El Niño climate phenomenon provides excellent insight into the consequences of climate change on marine mammals. El Niño is the result of a natural oscillation of atmospheric pressure over the Pacific Ocean. Periodically, winds diminish in strength, modifying the surface currents and ocean circulation. In the California Current, low abundances of macrozooplankton, mainly krill, have been associated with warm El Niño years. The same years, significant declines in prey for sea lions and seals are observed in several parts of the East Pacific. Consequently, the physiological condition of females wanes, the number of pregnant females drops, and mortality rates in newborns and young animals increase. Despite a return to normal conditions, sea lion and seal populations as well as fish stocks take several years to recover. In the waters of southern California, a change in the distribution of certain cetaceans has also been linked to El Niño and its consequences on the marine environment. After the disappearance of its favourite prey – a species of squid – the population of short-finned pilot whales that inhabited the coastal waters of California also abandoned the sector in search of its prey. When more normal conditions resumed and the squid returned, another cetacean species, the Risso’s dolphin, had already moved into the waters once occupied by the pilot whales.

North Pole, South Pole

Of all the regions of the planet, the poles are the most affected by climate change, notably in the form of melting ice. They are home to a number of cetacean species, whether they reside here year round (e.g. belugas and narwhals), or migrate here to feed (e.g. several species of rorquals). In Antarctica, the average air temperature has risen 2.5°C in 50 years. A number of researchers suspect that a reduction in ice cover is to blame for an 80% reduction in krill biomass since the 1970s in the Southwest Atlantic, near the Antarctic Peninsula. In winter, krill are believed to feed on microscopic algae in the ice. A loss of ice in winter would thus imply dwindling food resources for krill. Researchers are concerned given that krill represent the main food resource for whales in the Antarctic, including blue and minke whales.

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  • Photo credit: © Jean Lemire

In the Arctic, climate change has already had major consequences, with temperatures having risen 3 to 4°C in 50 years and the ice cap having retreated by 15 to 20% in the past 30 years. It is believed that the reduction in ice will represent a loss of important feeding sites for several marine mammals such as belugas and narwhals, which benefit from the accumulation of food resources at the edge of the sea ice. The rise in surface water temperatures is also thought to have an impact on ocean productivity. Marine mammals may therefore have more difficulty satisfying their hunger. Habitat loss also threatens ringed and bearded seals, which, after the polar bear, are the first marine mammals in Alaska to be considered endangered due to climate change. According to a study published in the scientific journal Nature, the thaw might also favour hybridization of species that most often share the same habitat, such as belugas and narwhals.

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  • Photo credit : © Jean Lemire

But impacts are not limited to polar regions. Two scientific studies observe the transfer of waters from the North Pacific to the North Atlantic, a phenomenon that last occurred nearly 8,000 years ago. This transfer will have multiple consequences: risk of new diseases, competition, parasites, modification of habitats, invasive species ranging from small planktonic organisms to cetaceans such as the killer whale, which is increasingly venturing into these cold environments, to the detriment of the local ecosystem.

And the St. Lawrence?

Over the past several years, researchers have observed a massive intrusion of cold waters from Labrador into the St. Lawrence. These waters have characteristics (temperature, salinity, plankton species) of their own and can alter the water masses of the St. Lawrence. Further, since the mid-1980s, the cold intermediate layer of the St. Lawrence Estuary and the Gulf of St. Lawrence has grown thicker and colder. These changes in the characteristics of the water masses will have ramifications on the St. Lawrence ecosystem.

The effects of such changes may already be underway. For example, it is suspected that the cooling waters of the Gulf of St. Lawrence over the past decade or so are to blame for the shift in the capelin’s range toward southern parts of the Gulf. Furthermore, the time series measured by Michel Harvey of the Maurice Lamontagne Institute (Fisheries and Oceans Canada) suggests a significant decline (in the order of 70%) of macrozooplankton in the Estuary and Gulf between 1994 and 2003. Researchers believe that this reduction might be attributable to climate change and the evolving characteristics of the water layers. And whereas krill represented 80% of macrozooplankton in 1994, this proportion fell to just 40% in 2003. In parallel, a new species – an amphipod of the cold Arctic waters whose scientific name is Themisto libellula – invaded the St. Lawrence between the early 1990s and the mid-2000s. And it didn’t go unnoticed: between 1994 and 2003, it represented between 2% and 45% of the biomass depending on the year. Changes in the communities of the St. Lawrence ecosystem, an important feeding ground for whales, might possibly have long-term effects on these titans.

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  • Mouth of the Saguenay, Tadoussac
  • Photo credit : © GREMM

In addition to modifying the characteristics of the St. Lawrence water masses, climate change is also feared to be altering some important oceanographic phenomena such as upwellings, a particularly significant phenomenon at the head of the Laurentian Channel, near Tadoussac. Fresher waters from the Great Lakes and the Fluvial Section of the St. Lawrence flow downriver and float over the more saline waters of the St. Lawrence Estuary. These waters are evacuated by the Gaspé Current along the southern coast of the Estuary and Gulf. This constant “loss” of water helps sustain an upstream current in the deeper waters from the Gulf to the Estuary. However, it is feared that reduced fresh water inflow caused by increased evaporation (global warming) and diminishing precipitation might undermine the pumping forces that allow deep waters to surface at the head of the Laurentian Channel. These waters transport krill (among other species), an important prey for the whales of the St. Lawrence Estuary.

Predict what is unpredictable

In addition to modifying the characteristics of the St. Lawrence water masses, climate change is also feared to be altering some important oceanographic phenomena such as upwellings, a particularly significant phenomenon at the head of the Laurentian Channel, near Tadoussac. Fresher waters from the Great Lakes and the Fluvial Section of the St. Lawrence flow downriver and float over the more saline waters of the St. Lawrence Estuary. These waters are evacuated by the Gaspé Current along the southern coast of the Estuary and Gulf. This constant “loss” of water helps sustain an upstream current in the deeper waters from the Gulf to the Estuary. However, it is feared that reduced fresh water inflow caused by increased evaporation (global warming) and diminishing precipitation might undermine the pumping forces that allow deep waters to surface at the head of the Laurentian Channel. These waters transport krill (among other species), an important prey for the whales of the St. Lawrence Estuary.

By combining scientific research with flexible management and protection tools, perhaps we can overcome a monumental challenge: predicting the unpredictable and making decisions today that will contribute to the whales’ recovery tomorrow.