Disease Studies

Leptospirosis outbreaks
The Marine Mammal Center continues to study leptospirosis, a bacterial disease that affects many mammals (including humans). In 2004, the disease occurred as an outbreak among California sea lions, kidney failure. Research suggests that the bacteria has actually adapted to sea lions and may be shed through “carriers,” or sea lions that are not outwardly suffering from leptospirosis, but continue to shed the bacteria through urine, thus infecting more sea lions. More research is underway to identify the DNA of this particular strain, and of the strains that affect other marine mammals. Further research may also result in improved treatments that not only cure the patient, but prevent shedding of leptospirosis and the spread of the disease.

Epilepsy in sea lions – studying the effects of domoic acid poisoning
Inquiry continues into the effects of domoic acid, a byproduct of harmful algal blooms or “red tides”, on sea lions. In 2007, the Center’s researchers published a paper in the Proceedings of the Royal Society identifying epilepsy in sea lions as a result of previous low dose exposure to the toxin. This is important, as similar effects could occur in people if they ate seafood containing these levels of domoic acid. Researchers plan on studying behavioral patterns of sea lion pups exhibiting epilepsy as a result of domoic acid exposure during development.

PCBs and developed risk assessment models
Polychlorinated biphenyls (PCBs) are mixtures of manmade chemicals such as oily liquids, solids or sometimes odorless vapors. They are no longer produced in the U.S. but are still found in the environment. When PCBs enter the water, fish ingest them and in turn, sea lions and other marine mammals and humans eat the fish. California sea lions are exposed to some of the highest levels of contaminants worldwide because of their geographical range. The Center analyzed blubber samples from female sea lions and their pups, and learned that the contaminants crossed the placenta, thus exposing fetuses during critical months of their development. This study helps set the parameters for developing risk assessment models for marine mammals.

Understanding the health of the Bay and its effects on harbor seals and potentially humans
The harbor seal habitat of Bay Area coastal waters is influenced by several human-produced factors, including sewage, agricultural and surface runoff, chemical pollution, and watercraft. Not only is it important to protect the seal population from toxic exposure that could threaten its survival, but the seals also serve as good gauges for the safety of the marine environment in relation to human beings. In 2007, the Center began a study looking at the prevalence and health effects of marine contaminants in the San Francisco Bay Area. Two harbor seal pup patients, Melissa and Nigel, were rescued by the Center because they were abandoned by their mothers. They were treated for umbilical infections and fed by staff and volunteers at The Marine Mammal Center until they were big enough to fend for themselves in the wild. During rehabilitation, the Center tested the seals for exposure to various pathogens and contaminants. Once healthy, the two seals were released wearing specially designed orange hat tags making it easier for scientists to chart their progress in the wild. The Center hopes to better understand the effects of this exposure on harbor seal survival. Ultimately, if seals, which feed at the same trophic level as humans, are affected by pathogens and contaminants in the marine environment, people could be too.

Conserving the nation’s most endangered pinniped - the Hawaiian monk seal
The Hawaiian monk seal is the most endangered pinniped in the U.S. with numbers estimated at around 1100 and decreasing at 4 % per year. Low survival rate of juvenile monk seals due to predation and malnutrition is the main factor causing the decrease in the population. As part of a joint conservation effort, The Marine Mammal Center embarked on a captive care project at Midway Atoll to provide nutritional supplementation to female juvenile monk seals in hopes of improving their chances of surviving in the wild to reproduce. This project was started in May 2006 by the birth of twin female pups at Midway Atoll. These two pups are the fourth known occurrence of twins in Hawaiian monk seals and the first pair that has been successfully weaned in recorded history. Both twins were undersized at weaning but were otherwise healthy. Because these were rare undersized female twins and given the history of poor juvenile survival, it was imperative to include the twins in the project. Five other female juveniles were included, and together with the twins were held in beach pens and fed a high-fat diet to make them gain as much weight as possible prior to release. More advanced medical care was provided when the seals exhibited signs of ill health. The twins, as well as four of the females, were released back into the wild at Midway Atoll at the end of March 2007.