Climate change What are the consequences for whales?

Climate change is a real and measurable phenomenon. Average water and air temperatures of many regions have changed, major ocean currents have been modified and both the Arctic and the Antarctic are melting at a troubling rate. The consequences of climate change on the marine environment are undeniable; although no one yet knows what effects these changes will have on whales. Even so, scientists predict that climate change will have an indirect impact on these giants through the modification of their habitat and by affecting their food resources.

Stir it up!

Ocean currents are the motor of the entire aquatic food web; they mix the various water layers, stirring up and redistributing the nutrients that in turn promote the growth of microscopic algae. They also contribute to the creation of favourable conditions for the accumulation of animal plankton and fish in specific areas such as cold water upwelling sites and ice-free polar zones known as polynias. These food-rich zones are often critical habitats for cetaceans. Water temperature, salinity and wind govern, in part, the great oceanic currents as well as local currents. These will definitely be altered by climate change. These changes could seriously modify whale habitat and affect their food sources.

The climatic effect known as El Niño is an excellent example that gives us a glimpse at the consequences of climate change on marine mammals. El Niño is the result of a natural oscillation of atmospheric pressure over the Pacific Ocean. The force of trade winds periodically diminishes, modifying surface currents and oceanic circulation. Low levels of macro zooplankton—essentially made up of krill—recorded in the California Current have been associated to warm El Niño years. A significant drop in the quantity of seal and sea lion prey has been noted in several areas of the Eastern Pacific during these same years. Consequently, the physiological condition and number of gestating females goes down, while the death rate of newborn and young seals and sea lions rises. Seal and sea lion populations, along with fish stocks, take several years to re-establish themselves, despite a return to normal conditions. Changes in the distribution of certain cetacean species have also been linked to the El Niño phenomenon and its consequences on the marine environment off Southern California. After the disappearance of its preferred prey—a species of squid—the population of short-finned pilot whales residing in coastal California waters left the area in pursuit of its prey. When conditions returned to normal, the squid also returned. However, by then another species of cetacean, Risso’s dolphins, had become established in the waters previously occupied by the pilot whales.

North Pole, South Pole

The regions of the planet most affected by climate change are the poles, notably through the melting of polar ice. Several species of cetaceans, including the beluga whale and the narwhal, reside in these areas. Others, including several species of rorqual whales, migrate to them to feed. The average air temperature in the Antarctic has risen by 2.5 oC in 50 years. Some researchers suspect that a decrease in ice cover is responsible for the 80 percent reduction in the biomass of krill near the Antarctic Peninsula in the South West Atlantic since the 1970s. In winter, krill likely feeds on microscopic algae contained in the ice. A decrease in the ice cover therefore implies a decline in winter food resources for krill. Researchers are worried because krill is the main food resource of Antarctic whales such as the minke whale and the blue whale.

The effects of climate change in the Arctic are already evident. Temperatures have risen by 3 to 4 oC in 50 years and the ice cap has retreated by 15 to 20 percent over the past 30 years. The decrease in the ice cover could lead to a major loss of feeding sites for several species of marine mammals, like beluga whale and the narwhal, which take advantage of the accumulation of food at the limit of the pack ice.

Predicting the unpredictable

Will measures taken today to manage whale populations still be appropriate within the context of a habitat that is undergoing rapid transformations due to climate change? A case in point are the Marine Protected Areas (MPAs), which are often established for the express purpose of assisting specific cetacean populations by protecting their critical feeding areas. Yet, these areas may be altered or moved due to climate change. Should the concept of MPAs not then be more mobile and adaptable, taking into account the potential effects of climate change? Another example is whaling management. The International Whaling Commission is under mounting pressure from some of its member countries to lift the commercial whaling ban. The basis of this request resides in the increase of several whale populations. However, taking into account concerns about climate change, is it still advisable to prone the resumption of large-scale commercial whaling activities?

By combining scientific research with flexible management and protection measures, we may be up to the enormous challenge of predicting the unpredictable and making present-day decisions that will contribute to the future recovery of whales.

What about the St. Lawrence?

Researchers have been detecting a massive intrusion of cold water from Labrador into the St. Lawrence for several years now. These waters have specific characteristics—temperature, salinity and plankton species—that have the potential to modify St. Lawrence water masses. Moreover, the cold intermediate layer of water present in the Gulf and Estuary of the St. Lawrence has become thicker and colder since the mid-1980s. These changes in the composition of water masses will have consequences on the St. Lawrence ecosystem.

It is possible that the effects of these changes are already underway. Researchers suspect that the cooling down of Gulf of St. Lawrence waters over the past 10 years could be responsible for the relocation of the capelin home range towards the southern Gulf. Furthermore, the timeline measured by Michel Harvey of the Maurice Lamontagne Institute (Fisheries and Oceans Canada) suggests a major drop of 70 percent in the amount of macro zooplankton in the St. Lawrence Estuary and Gulf between 1994 and 2003. Researchers believe that this reduction could be explained by climate change and changes in the characteristics of water layers. Also, although krill accounted for 80 percent of zooplankton in 1994, it represented a mere 40 percent by 2003. At the same time, vast quantities of a new species have shown up in the St. Lawrence since the early 1990s: a cold-water Arctic species of amphipod known as Themisto libellula. This species has not gone unnoticed; from 1994 to 2003 it represented between 2 percent and 45 percent of the biomass depending on the sampling year. It is possible that changes in St. Lawrence ecosystem communities—a major food source for whales—could have long-term effects on these giants.

As well as modifying the characteristics of St. Lawrence water masses, there is concern that climate change could modify major oceanographic phenomena such as cold-water upwellings. This natural event is particularly important at the head of the Laurentian Channel near Tadoussac. Fresh water from the Great Lakes and the fluvial portion of the St. Lawrence flows downstream and floats on the saltier waters of the St. Lawrence Estuary. This water is evacuated by the Gaspé Current along the South Shore of the St. Lawrence Estuary and Gulf. The constant “loss” of water sustains an upstream current of deep water from the Gulf towards the Estuary. There is now concern that a reduction in the amount of freshwater flowing out of the St. Lawrence—because of increased evaporation due to climatic warming and less precipitation—could diminish the forces that pump deep waters to the surface at the head of the Laurentian Channel. Among other things, these deep waters transport krill, which is an important prey species for the whales of the St. Lawrence Estuary.

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The International Arctic Science Committee

The United Nations World Conservation Monitoring Centre, department of Biodiversity and Climate Change