Whales, sea turtles and salmon
Oceans are disproportionately affected by climate change. For decades, the oceans have slowed the rate of surface warming on Earth by absorbing carbon dioxide from our atmosphere. The consequences for marine life are significant, from ocean acidification and coral reef bleaching to coastal habitat erosion, increased intensity of storms and shifting ocean currents.
Scientists aren't entirely sure why whales migrate. While terrestrial animals and birds typically breed in their temperate summer habitats, migratory whales head for the icy waters of the Arctic in summer solely to feed, returning to their warm water to breed despite relatively scarce food in their winter habitats. Researchers previously theorized that whale migration could be a strategy to increase calf survival by reducing predation, or by allowing them to devote more metabolic energy to growth instead of keeping warm. More recently, researchers have speculated that whales may head for warmer waters in time for molting, a period during which they enlarge blood flow through their skin, making it harder to conserve body heat in cold water.
A 2015 study of whale populations in the Gulf of St. Lawrence (Canada) discovered that between 1984 and 2010, both fin and humpback whales shifted their annual arrival dates forward by more than one day per year, maintaining a consistent two-week gap in their arrival as they independently adapted to earlier ice break-up and rising sea surface temperatures that researchers believe triggered earlier production of the krill and small fish they feed on. However, the authors noted that the species' departure dates shifted at different rates, which they worry could start to erode the temporal separation that historically allowed them to share the same summer feeding grounds.
Humpback whales face challenges in their winter breeding grounds as well. A study published in July 2022 projects that if humanity doesn't reduce our fossil fuel emissions, up to two-thirds of their winter breeding grounds will become unsuitable habitat for humpback whales, with surface temperatures consistently at or above the upper limit that the whales can tolerate.
Climate change is upending humanity's relationship with the ocean in more ways than one, compounding the overfishing crisis that has steadily escalated since the 1990s. Despite the dire outlook, many experts believe that seafood could be the most promising way to sustainably feed growing populations while adapting to, and even slowing, climate change.
EDF and partners around the world are working to elevate seafood’s role in addressing food insecurity, particularly in tropical developing nations, and to open new opportunities for sustainable and resilient marine ecosystems and the communities that depend on them.
Sea turtles, like whales, migrate between feeding and breeding grounds. While the migration happens each year, not all individuals migrate each year. The journey to breeding and hatching grounds is typically only made by sexually mature adults, and these long-lived creatures — with life expectancies of 50-100 year or more depending on the species — can take several years or even decades to reach maturity.
Green turtles reach maturity at 25-35 years of age, and undertake reproductive migration every 2-5 years of their adult lives, typically returning in late spring to the same beaches where they hatched. Females mate with males along their entire journey, stay for several months and lay hundreds of eggs in multiple nests before departing for their foraging grounds.
The endangered Kemp's ridley sea turtle is the smallest sea turtle in the world. Although they're found primarily in the Gulf of Mexico, their range extends along the eastern seaboard of North America, as far north as Nova Scotia! Unusual among sea turtles, they nest en masse, arriving to their nesting beaches in northeastern Mexico in large groups locals call arribadas (Spanish for "arrival").
In the last decade, wildlife rescuers on Cape Cod, Massachusetts began seeing a heartbreaking increase in migratory sea turtle strandings on the cape, victims of "cold-stunning" — a condition similar to hypothermia that can progress to shock, pneumonia, frostbite and even death. The majority of the stranded turtles were Kemp's ridleys, who had followed the coastal warm water currents all the way to the Gulf of Maine.
Experts believe the warm water currents and the local geography confused turtles attempting to return south and ending up in the Cape Cod Bay, bordered to the south by a curved peninsula. That means to leave the bay and reach open water, they must first swim north into colder waters, going against their powerful instinct to head south. They end up stuck in the bay as temperatures drop to dangerous — even deadly — lows.
Migration has a substantial cost for animals. All other things being equal, to remain in one location requires less expenditure of calories than to make an arduous and lengthy journey. Species that undertake annual migrations therefore typically evolved, over a very long time, to do so because the benefits of reaching another territory outweighed the metabolic costs of getting there enough to provide a long-term evolutionary advantage over individuals who didn't.
Salmon are one of the most well-known aquatic migrators. Many dramatic photos have captured the sight of dozens of salmon leaping into the air as they fight against the river current to reach their spawning grounds upstream.
Recently, researchers have theorized that the costs of migration may soon become too steep for Chinook salmon to bear. Salmon prefer cooler waters and experience cardiovascular stress from sustained time spent in warm waters. It takes a lot of energy to leap over rocks and swim against rapids, so salmon must frequently pause to rest and replenish energy in calm waters along the way.
Unfortunately, those calm waters are heating up, making them less restful and depriving migrating salmon of the energy they need to complete their migration.