Climate Change Impacts on Marine Mammals

By Jessica Boswell

Jessica Boswell is a student in the Environmental Studies Department at the University of California, Santa Barbara. She is specializing in species conservation policy and ecology with an outside concentration in marginalized community politics. She is researching terrestrial and marine community dynamics on the Palmyra Atoll as it undergoes various conservation projects.

Gray whales are washing up emaciated on beaches in California, Oregon and Washington. There is an uptick in whales becoming entangled in fishing gear in nearshore waters. Krill, a critical food sources for whales, appear to be in lower numbers in some areas of the ocean.

What’s going on?

As oceans warm at a shocking rate, marine mammals are becoming increasingly vulnerable to a multitude of threats. While there is strong science demonstrating a causal link between a warming atmosphere and declining survivability of several marine species, it is difficult to draw definitive conclusions in many cases due to research constraints. Thus, potential solutions are often limited and uninformed.

In fall of 2022, marine scientists from the Marine Mammal Commission, the National Oceanic and Atmospheric Administration, and other research institutions banded together to review the current scientific literature regarding the effects of climate change on marine animals, creating a comprehensive catalog of suspected, likely, and known impacts. Their review encompassed impacts on whales, seals, dolphins, walruses, and other marine mammal species from the subtropical waters, temperate waters, and Arctic waters of the United States. Additionally, they investigated the shortcomings of research that currently greatly restrict the possibilities of species conservation.

Their findings suggest that the most obvious known impact of climate change in U.S. waters is shifting distributions of marine mammal species. As global atmospheric CO₂ rises, ocean temperatures rise as well, sometimes forcing entire populations of marine mammals to relocate to find suitable habitats. Unfortunately, as these species colonize new environments, they encounter new threats.

For the North Atlantic right whale (Eubalaena glacialis), the movement north towards colder waters caused an increase in entanglements in fishing gear and an escalation in the number of injuries and deaths from ship strikes. Climate-induced distribution shifts also impacted reproduction by affecting the right whale’s access to prey.

Similarly, in California, humpback whales (Megaptera novaeangliae) were found following their prey towards land during marine heatwaves, where they became frequently entangled in crab gear. Interestingly, the presence of crab gear was itself a result of climate change as well, as warmer temperatures caused a disease outbreak in the crab population that delayed the catching season. In some areas in California, when whales are present, crab season is delayed to avoid entangling humpback and other whales.

Aside from altered distribution and subsequent entanglement, the authors discovered that, across the literature, marine mammals are experiencing “increased mortality as a result of human activities, poorer body condition, reduced reproductive success, and more predation,” all of which decrease the survivability of the species and overall ecosystem.

While there are several cases of climate change directly impacting marine species, it has proven difficult to determine causation in many circumstances. In recent years, Eastern North Pacific gray whale (Eschrichtius robustus) populations declined dramatically for unknown reasons. Scientists have hypothesized that it is related to significant shifts in the Arctic landscape and sea ice which could be affecting prey accessibility or increasing the presence of deadly algae blooms, but there has yet to be tangible evidence found linking the changing climate with this unusual mortality event.

Similarly, scientists cannot concretely link climate change to disease outbreaks in marine mammals, although warming temperatures are predicted to be driving pathogens into habitats where they were originally undetected. For instance, Vibrio parahaemolyticus, a bacterium that can cause human illness, has been identified in new regions and in new species. Sadly, there isn’t enough investigative ability and funding for scientists to demonstrate a strong link to climate change or to even prove that this bacterium is causing harm to marine mammals.

The findings of this expansive literature review suggest that current research has, in some cases, failed to causally link climate change to a decline in the survivability of some marine mammal species. The authors attribute this chronic uncertainty to a lack of resources for proper investigations, especially for species inhabiting deeper waters, and offer several suggestions on how research and conservation efforts can be improved.

First, the authors insist that a “long-term, systematic collection of health data coupled with routine integration of information from multidisciplinary research programs and local observations” is necessary to provide proper conservation recommendations.

To accomplish this, scientists propose a more holistic approach to research that integrates the larger ecosystem. Climate change is a complex, multifaceted issue, and to keep up, it is necessary for researchers to consider the entire picture rather than focusing on small-scale problems. Mitigation will be short-term at best if science does not take a holistic, multidisciplinary approach to addressing climate change impacts on marine mammals. Scientific investigation should include large communities of species. It should also examine how overarching environmental processes, including algae blooms, sea ice, and disease, affect marine species to better analyze the possible severity of climate impacts.

Additionally, solutions need to be dynamic because climate change is dynamic. We have seen how climate change quickly and dramatically impacts landscapes, often in ways that we cannot predict. The authors assert that “management structures must become more agile so that effective actions can be implemented rapidly and adjusted as needed.” Some communities are effectively initiating holistic conservation efforts, but these mitigation strategies can only take us so far as long as we continue to dump greenhouse gases into the atmosphere.

The survivability of the entire marine ecosystem hinges on our ability to improve research efforts on a global scale and cooperate internationally to address the root of the problem: our overreliance on fossil fuels.

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The International Marine Mammal Project of Earth Island Institute has been allied with many fellow organizations in opposing offshore oil drilling, which contributes to global warming and threatens our oceans with oil spills, intense noise from prospecting and drilling, and fosters continued dependence on oil and gas. We advocate for the removal of dams to restore salmon streams, necessary to feed orcas and other marine mammals. We need to transition to alternative sources of energy, such as solar and wind, to offset the damage of global warming on ocean and terrestrial life. Please help with a donation to protect marine mammals from global warming. Thank you!