Cetaceans are a group of marine mammals composed of whales, porpoises, and dolphins. Although they’re ecologically, economically, and culturally important, cetaceans are facing growing threats around the world. Today, six of the 13 great whale species are endangered or vulnerable. In Canada, 19 whale populations are designated as endangered, threatened, or of special concern. Why is this?
For starters, whales and other cetaceans are K-strategists: meaning they’re large, have long lifespans, and don’t reproduce very often. Harvesting an individual from a whale population has much greater repercussions than harvesting an individual from a salmon population, as salmon have greater reproductive rates and more individuals in their population.
This means that small changes in whale mortality and reproduction at the individual level can make a difference at the population level. Whale populations can of course be influenced by natural changes affecting prey availability, species competition, and ocean habitats. However, such changes are typically exacerbated by human beings. Overall, major threats to cetaceans are often the result of either direct or indirect human activity, and include habitat degradation, commercial fishing and whaling, pollution, boat traffic, and climate change.
Habitat degradation is a broad term referring to the human processes that make habitats less suitable for other organisms. Essentially, a degraded habitat is the product of other environmental drivers such as human-caused climate change, coastal development, boat traffic, introduced species, overfishing, and pollution—factors that make habitats less suitable for whales.
Commercial fishing and whaling
The blue whale, humpback whale, and North Atlantic right whale were nearly hunted to extinction in the 19th and 20th centuries. In 1986, the International Whaling Commission (IWC) introduced a moratorium on commercial whaling, although Iceland, Japan, and Norway still continue commercial whale hunts, killing several hundred whales each year.
The commercial fishing industry is a much greater threat to whale populations than direct whale harvesting, however. An estimated 300,000 cetaceans are accidentally caught each year as bycatch, trapped in the fishing gear of both large commercial fishing vessels and local artisanal ones. This is a global problem, affecting not only cetaceans but other marine mammals, sea birds, and turtles. On top of that, unsustainable commercial fishing can reduce fish populations, decreasing prey availability for certain cetacean species.
Pollution is perhaps the most direct example of habitat degradation and poses a risk to both ecosystem and whale health. Contaminants can originate from coastal and offshore energy development, boat traffic, cities, human products and waste, and tourism. Oceans are often the final destination for many contaminants travelling from lakes and rivers.
Chemical pollutants include human-made endocrine-disrupting persistent organic pollutants (POPs) that can interfere with reproductive success, polychlorinated biphenyls (PCBs) that accumulate in organisms at the top of the food chain like whales, and contaminants such as mercury that can lead to reproductive and neurological problems. Agricultural runoff can overload rivers and oceans with nutrients, degrading water quality and leading to algal blooms. What’s more, whales can ingest and become entangled in larger marine debris such as glass, plastics, and fishing gear.
Chemical pollution is not the only danger, however. Noise pollution, or anthropogenic sound, is another threat to whale habitat and survival, as whales heavily depend on sound for foraging, migration, and reproduction. Acute noise, which is intense and short-lasting, often comes from seismic surveys and military sonar, while chronic noise, which is lower intensity and longer-lasting, often originates from shipping and industrial activity.
Boat traffic from fishing vessels and industrial shipping is only increasing, particularly in the Arctic as the ice melts and shipping routes open up. This is bad news for whales, as it adds not only to the anthropogenic noise problem but also to the prevalence of ship strikes, which can injure or kill whales. Off the US west coast alone, approximately 80 whales are killed every year, although ship strikes are rarely witnessed and mortality estimates are likely underestimates.
Noise pollution and ship strikes from boat traffic are not just from fishing and shipping vessels; boats used for recreation, research, and tourism are also part of the problem.
Climate change impacts are widespread and complex, including changes in temperature, sea ice, ocean acidity, rainfall, and climate patterns. These factors will not only change food webs and alter ocean physics; they will also aggravate already existing threats, such as pollution and disease. Climate change could potentially increase the development of pathogens and disease transmission in whales.
In response to changing ocean temperatures and prey abundance and availability, climate change may also cause some whales to shift their ranges or migratory routes, disrupting breeding patterns and fragmenting species ranges. Arctic-residing species such as the bowhead whale, narwhal, and beluga are particularly susceptible to ecological changes caused by warming ocean temperatures and melting sea ice.