The Department of Vertebrate Zoology at the Santa Barbara Museum of Natural History has been collecting marine mammal stranding data for many years, even before the California Marine Mammal Stranding Network (CMMSN) was established. With a considerable database already in hand, our previous curator, the late Dr. Charles Woodhouse, became a founding member of the network. When local marine mammal rehabilitation facilities were established, Chuck worked closely with them to collect data and voucher specimens from stranded marine mammals. On going participation in the network provides our staff with unique opportunities to build the Museum's marine mammal research collection.
During the past 30 years, we have responded to almost 300 stranded cetaceans and have developed a diverse collection of skeletal and tissue samples. On average we respond to about 7 dolphin and 3 whale strandings per year in the tri-county area, although some years we experience an unusual increase in these numbers. 2002 was an exceptionally high year due to a domoic acid event.
DOMOIC ACID TOXICITY
Dr. Charles J. Rennie III
Adjunct Curator of Marine Mammals, Department of Vertebrate Zoology
Domoic acid is the result of an extreme proliferation of marine algae, usually (but not always) of the genus Pseudonitzschia (see below). This compound affects particularly the hippocampus and amygdala in the brain, where it causes both degeneration and scarring (gliosis). It acts like glutamate, the main excitatory neurotransmitter in the brain; an excess of which can cause cell death.
Domoic acid toxicity was first recognized on Prince Edward Island in Canada in 1987, when there was an outbreak of neurological symptoms among humans who had eaten mussels. Four people died, and a number of others suffered severe short-term memory impairment as well as other neuropathies. Domoic acid toxicity has been postulated as a cause of mortality in marine birds, although major die-offs have not been well enough investigated to confirm it as the definitive cause.
Domoic acid was first pinpointed as a problem in marine mammals in 1998, when many California sea lions (Zalophus californianus) died along the Central California coast. Seizures were the most common symptom, although abnormal scratching, head-bobbing, and ataxic ("drunken") movements were also seen. High levels of domoic acid were documented in anchovies, but not in local shellfish. Domoic acid toxicity may be responsible for multiple previous die-offs of pinnipeds, although studies were not sufficient to pinpoint it as the definitive cause.
In the current die-off of common dolphins (Delphinus sp.), domoic acid toxicity was first postulated by colleagues in Northern California and at the Los Angeles Museum of Natural History. Most of the affected dolphins appear to have been in otherwise excellent health: most were young otherwise healthy looking males, with few parasites. Tissue samples have been collected, as well as blood, urine, and feces, wherever possible. Several animals have tested positive for domoic acid in various fluids and tissues. The deaths are continuing. What is now needed is more information about the current Pseudonitzschia bloom and domoic acid levels in species preyed upon by marine mammals for food. Close monitoring of local shellfish and fish caught for human consumption is also needed; there may be some risk to humans here!
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