The general public is becoming increasingly aware of the link between the oceans and human health: the oceans supply food for more than half the world’s population and they influence the global climate system. The health of an ecosystem depends in part on the capacity for acclimation and adaptation of the species that comprise it. Studying how animals react to a changing environment allows us to make predictions about whether animals can survive and/or thrive under a particular set of natural or artificial conditions. Research projects at Hubbs-SeaWorld Research Institute (HSWRI) are examining a number of physical and biological factors that influence the health of marine ecosystems.
For over 40 years research scientists at HSWRI have been at the forefront of developments in technologies and techniques for studying the demography, movements, foraging ecology, physiology, and medicine of marine mammals in California and around the world. Research programs that span many decades are unusual for large mammals. The Institute’s long-term research on the Channel Islands provides a foundation for addressing questions about the factors that limit and regulate marine mammal populations and that drive their interactions with humans. These factors include the influence of infectious and non-infectious diseases on marine animal vitality, performance and population growth.
California sea lions, northern elephant seals and harbor seals were absent or at low abundance in the North Pacific through the last quarter of the 19th Century due to long periods of harvest by aboriginals. Subsequent unregulated hunting, poaching, and bounty killings by Europeans added to their decline. With the end of hunting of these species in U.S. and Mexican waters, their range and abundance began increasing steadily.
The primary worldwide breeding colonies of northern elephant seals and California sea lions occur on the California Channel Islands. These two species have been increasing at exponential rates for six decades or longer. Some evidence suggests they are more abundant now than at any time in history. The seal and sea lion breeding habitats on the islands and nearby waters are protected under the jurisdiction of the U.S. Navy (e.g., San Nicolas Island), the Department of Interior (Channel Islands National Park), the Department of Commerce (Channel Islands National Marine Sanctuary) and the state of California (Channel Islands Marine Protected Areas). However, pinnipeds (seals and sea lions) have increased their use of mainland beaches in recent years, resulting in high profile conflicts with human activities and property. California sea lions haul out on (and occasionally destroy) boats, docks, piers and jetties at marinas along the west coast of the U.S. A small population of harbor seals on an urban beach in Southern California has generated intense conflict, including lawsuits and arrests, among residents and local officials; beach closures due to contamination from harbor seal fecal coliform bacteria also occurs. Wandering northern elephant seals have caused traffic collisions on a busy north-south highway in central California.
The movements of these apex marine predators take them from source populations in California waters throughout a broad range of local, state and national jurisdictions. Understanding the factors affecting these populations, particularly as ocean climate changes, is critical to predicting and documenting their interactions with coastal and high seas resources. Pinniped populations may be reservoirs for pathogens that can harm terrestrial species, particularly food animals. Conversely, ‘pathogen pollution’ from agricultural and urban run-off is causing disease in coastal marine mammals. An understanding of the factors regulating seal and sea lion populations in the region is key to proactive management of these protected species.
Influenza virus infection in marine mammals in California
Hubbs-SeaWorld Research Institute (HSWRI) scientists and their colleagues demonstrated that three co-occurring marine mammal species in California recently were exposed to a pandemic influenza virus. This virus (A[H1N1]pdm09) is most similar to a December 2009 human isolate from San Diego. http://www.nature.com/emi/journal/v2/n6/full/emi201340a.html
The authors documented widespread exposure to the virus among wild northern elephant seals (sampled at the California Channel Islands) and seals that had stranded along the central and northern California coast. Antibodies to the virus also were detected in a small number of California sea lions and harbor seals, but there was no evidence of widespread transmission in these two species. None of the animals that were tested showed clinical signs of the disease.
Elephant seals were hunted nearly to extinction in the 1800s. The species has since rebounded to over 170,000 animals today, but this severe demographic and genetic bottleneck appears to have taken a toll. Several studies by HSWRI scientists and others have shown very little genetic variability in the species, and this reduced variability may make elephant seals more susceptible to viruses than are harbor seals or sea lions.
This study demonstrates the importance of long-term interdisciplinary studies such as those conducted by HSWRI scientists and their collaborators on marine wildlife in California. This research is documenting the influence of infectious and non-infectious diseases on free-ranging animals, including zoonotic diseases (those transmissible from animals to humans) and diseases such as this influenza virus that can affect both animals and humans. Marine mammals may play a role similar to swine as reservoirs and mixing hosts for influenza viruses. Future studies are aimed at better understanding the relationships between influenza viruses and their human and marine animal hosts.
Physiology & Ocean Health
Understanding How Animals Respond to a Changing World