Marine Mammals serve as ecosystem health indicators as their diets and habits become affected by climate change
As climate change has ravaged our local ocean, marine mammals that generally top the food chain have struggled, and some populations may be hard pressed to recover.
Locally, common marine mammal species include harbor seals, Northern elephant seals, California sea lions, gray whales, humpback whales, orcas, Pacific white-sided dolphins, Risso’s dolphins, common dolphins, bottle-nosed dolphins and harbor porpoises.
Rare but not unheard of species include California sea otters and Stellar sea lions, blue whales and minke whales. While these animals are inarguably the top of the food chain, challenged only by our local great white shark population, that has not saved them from the effects of climate change.
In 2019 alone 37 gray whales, one of our iconic native species, have washed up dead on local shores, most of them suffering from emaciation and severe malnutrition. An additional 118 have washed ashore along the entirety of the west coast. Others animals, from whales and dolphins to seals and sea lions, have altered their behaviors, historic ranges and seen ill health effects from the damage done to their ecosystem.
According the Marine Mammal Center, “Marine mammals are ecosystem indicators, and the health of these animals provides insights into human and ocean health threats.”
The Marine Mammal Center, located in Sausalito, rehabilitates and releases over 600 seals, sea lions and otters a year and performs significant research on a variety of local marine mammal species.
Among the effects they’ve seen that can be traced to climate change include the rising sea level, warming water temperatures and increasingly acidic water.
Rising sea levels can impact the availability of habitat for resting, birthing and nursing. Locally, Northern elephant seals have had their historic pupping grounds reduced, leaving babies vulnerable to storm surges and premature separations of mothers and pups.
While marine mammals themselves are less affected by warming water temperatures than cold-blooded sea creatures, their primary food sources are often greatly affected. Schooling fish, such as sardines and anchovies, staples of local marine populations, tend to dive deeper and stay further offshore in the hunt for cooler waters, forcing their predators to expend greater amounts of energy to find them.
According to the Marine Mammal Center, 2015 in particular saw a huge spike in sick adolescent sea lions, as mothers abandoned pups to go in search of food, and older pups struggled to travel and dive far enough to catch prey.
Acidic ocean water, caused by changing water temperatures, can lead to dramatic algal blooms, and in this area, that can lead to a particularly deadly outcome, for humans and marine life alike.
“One particular diatom, Pseudonitzchia australis, responsible for producing a toxin called Domoic acid toxicosis, is one that could have dramatic effects on marine mammal populations,” according to the Marine Mammal Center web page. “First identified in 1998 by The Marine Mammal Center, this toxin accumulates up the food chain and can cause seizures, disorientation and brain damage in animals that feed at the top of the food chain. In 2015, with record warm water temperatures, the largest algal bloom in history was observed off the west coast of the United States and resulted in over 200 sea lions suffering from Domoic acid toxicosis and also shutting down fisheries, such as Dungeness crab and razor clams, to human consumption.”
A paper from the World Wildlife Federation on the effects of warming oceans on cetacean (whale, porpoise and dolphin) populations found that “breeding in many species may be timed to coincide with maximum abundance of suitable prey, either for the lactating mother or the calf at weaning. Therefore, any changes in the environmental conditions that determine prey abundance may cause a mismatch in synchrony between predator and prey, either in time or location. Migratory cetaceans that travel long distances between feeding and breeding areas may be particularly vulnerable to this mismatching.”
Sea level rise may, on the face of it, not seem problematic for species which spend their entire lives in the water, but the paper points out that “important habitats for coastal species and species that require coastal bays and lagoons for breeding, such as gray whales and humpback whales, could be adversely affected.”
Finally, the paper points out that since climate change is not the only threat faced by cetaceans, a shifting of their home habitats or migration patterns could result in the animals leaving sanctuaries or other real estate set up to protect them.
“This could be a particularly important issue for relatively small protected areas that have been established to conserve specific populations, or habitats used for critical parts of an animal’s life history, such as breeding or calving,” it concludes.
Gray whale deaths launch NOAA study
On May 30, the National Oceanic and Atmospheric Association launched an investigation into the unusual spike in gray whale stranding and deaths along the west coast, labeling it an “unusual mortality event.”
According to NOAA, this is the largest number of dead gray whales washed ashore since 2000. Gray whales migrate along the west coast from winter waters in Mexico where they give birth to summer feeding grounds off Alaska. The whales rely largely on their summer feeding in the Arctic to last them throughout the year because they do not feed extensively while migrating or wintering in Mexico.
Many gray whales that have stranded this year have been skinny and malnourished, with some showing signs of emaciation, suggesting that some whales may be exhausting their energy reserves this year before they reach the Arctic to resume feeding, according to NOAA researchers.
On June 7, U.S. Sen. Dianne Feinstein (D-Calif.) released a statement on the whale deaths. In part it said, “More dead gray whales have washed up on west coast beaches this year than ever before, a likely result of human-caused climate change. It’s heartbreaking that so many of these magnificent creatures have perished because we continue to take little or no real action to combat global warming ... the National Oceanic and Atmosphere Administration has now declared the elevated gray whale strandings along the West Coast an ‘Unusual Mortality Event’ and is devoting more resources to study it.
“Early reports show that many of the whales starved to death because they had an inadequate food supply during their feeding season in Arctic waters. Scientists believe the loss of sea ice due to climate change has disrupted the Arctic ecosystem and reduced the population of shrimp-like amphipods, the gray whale’s main source of food. This means whales are starving to death during their long migration north after the breeding season in Mexican waters.
“Gray whales are what is known as an ‘indicator species’ for ocean health, a measure of how well or poorly the oceans are faring. These deaths are further proof that climate change is having a profoundly harmful effect on our planet.”