Common Dolphin (Delphinus sp.) Unusual Mortality Event of 2002

Michelle Berman and Krista Fahy
Department of Vertebrate Zoology, Santa Barbara Museum of Natural History, Santa Barbara, CA

This Poster Presentation won 1st Prize in the 2002 Student Poster Contest.

Between February and May 2002, the Vertebrate Zoology Department at the Santa Barbara Museum of Natural History responded to 31 Common dolphin (Delphinus sp.) strandings. This event was deemed an unusual mortality event and responders were requested to collect critical data to determine cause of death. Data collection consisted of morphometrics for all animals and a field or laboratory necropsy depending on the level of decomposition. Field necropsies consisted of stomach, urine and fecal collection while laboratory necropsies included a comprehensive collection of weight and samples of all organs. Of these stranded dolphins, 81% were males (n=25). The suspected cause of death based on behavioral indications (i.e. dolphins seizuring on the beach) appeared to be domoic acid toxicity due to ingestion of affected prey. All of the specimens analyzed from 16 dolphins indicated a presence of this biotoxin. The content of 17 stomachs was analyzed revealing a variety of prey items including anchovy, hake, sanddab, smelt, shiner, perch, rockfish, white croaker, squid and octopus. Two of the stomachs were empty. Five serum samples were analyzed for cetacean morbillivirus titers and all tested positive for these antibodies. Complete histopathological analysis has been completed on 4 dolphins and several pathological anomalies were present. This pathology is commonly seen in other stranded cetaceans and deemed "clinically insignificant". This is the first documented domoic acid related mortality event for common dolphins. A total of 96 cetaceans reportedly died during this period although some results are still pending. Mortality events such as this allow researchers a unique opportunity to examine the life history of a relatively select population and the data collected will provide detailed insight into common dolphin biology.