Research conducted by Dr. Logan Pallin, Postdoctoral Researcher, Department of Ocean Sciences, UC Santa Cruz
Monterey Bay is home to one of the most diverse and abundant assemblages of marine mammals in the world, but little research has been done to analyze how the runoff from chemicals used in local agriculture and industry impact marine mammal behaviors and health in the bay. To address this knowledge gap, between 2023-2025, researchers analyzed blubber from humpback whales and blood samples from sedated sea otters and California sea lions. These animals are “sentinel species,” meaning they act as indicators of ecosystem health. Sea otters reside and forage locally in estuaries and coastal waters year-round; California sea lions forage more broadly within Monterey Bay yet are also year-round residents; and humpback whales are only seasonal residents and forage over a broad spatial range during spring and summer months.
The samples collected cumulatively revealed the presence of at least 144 different Halogenated organic compounds (HOCs). Many are byproducts of polychlorinated biphenyl (PCB), which is used in a variety of industrial processes, or the pesticide dichloro-diphenyl-trichloroethane (DDT). These are chemicals referred to as “forever chemicals” because they persist in our environment and bodies. Both were banned in the 1970s.
The matrix on view visualizes a sample toxin load from each of the different species. It shows all the HOCs found in a male humpback whale called ‘Batman,’ who has been regularly sighted in Monterey Bay since the 1980s, a group of juvenile female sea lions, a group of adult female sea lions, and a group of adult female sea otters. Humpback whales were found to carry the most toxins and sea otters the fewest but in higher concentrations. Batman was found to have more than 108 different chemical compounds in his system, including DCPA, an herbicide banned in 2024 by the EPA. Juvenile female sea lions show many toxins not found in reproducing females. This indicates that mothers offload toxic chemicals to their offspring through gestation and their milk, reducing their own toxic burden. In contrast, non-reproducing females and males retain these chemicals throughout their lifespan, which can reach up to 80 years—similar to that of humans.
Many of the chemicals likely found their way into Monterey Bay and then into the animals from nearby farmlands and industry via the rivers and estuaries, and from the DDT dump site off the coast of Southern California. Large-scale climatic events, like heavy rains, can exacerbate the spread of chemical runoff. For instance, in March 2023, a breach in a section of the Pajaro River levee led to the flooding of farmland, leaving chemical residues in the soil and making the land unusable for weeks. Since these findings, in January 2025 a fire at Moss Landing Power Plant released heavy metals in Monterey estuaries. Further tests are needed to determine the implications for marine mammals.
