collaborative research on the assay of brevetoxins in marine animal tissues; this process 

 should assist in the further development and verification of the assays. A major difficulty in 

 establishing an assay of this type is obtaining a true "control liver" sample, known to be free 

 of toxins or other substances that interfere with the assay. 



Contaminants 



Tissues from a sub-set of the stranded bottlenose dolphins were examined to 

 investigate the possibility that environmental contaminants may have caused or contributed 

 to the observed strandings. Blubber and liver samples from 20 of the stranded bottlenose 

 dolphins were analyzed for chlorinated hydrocarbons (CHs). In addition, liver and kidney 

 samples of these dolphins were analyzed for certain metals. 



The concentrations of mercury in the livers of 2 dolphins (114 and 117 jig/g or ppm 

 based on wet weight) were notably elevated and may be of toxicological concern. The 

 concentrations of total CHs in the 20 animals sampled varied widely; 3.0-190 ppm in blubber 

 and 0.5-58 ppm in liver with eight dolphins having levels of total CHs in blubber that were 

 greater than 50 ppm. Interestingly, relative levels of DDT, compared to the levels of DDE 

 (a metabolite of DDT), in three of the dolphins may indicate an exposure to relatively 

 recently released DDT. 



The concentrations of CHs and certain metals, especially mercury and selenium, in 

 some of the dolphins were sufficiently high to warrant a more systematic study of 

 contaminant exposure of this species and of potential health effects due to this exposure. In 

 addition, special efforts are needed to investigate possible sources of certain toxic chemicals; 

 including CHs and aromatic hydrocarbons, by measuring parent compounds and their 

 metabolites in tissues and stomach contents of these animals. 



Summary 



The investigation did not provide any conclusive evidence of a single causal agent, or 

 multiple causal agents, for the increase in strandings. Available abundance estimates indicate 

 that bottlenose dolphin abundance may have been higher in the nearshore northwestern Gulf 

 during the spring and summer of 1990 than during 1984; however, the 1990 estimates are 

 limited in geographic scope and may not reflect the overall abundance patterns. No 

 statistically significant differences were found between the 1990 and the 1984-89 age 

 structure of the stranded animals. But, possible biases in the 1984-89 age sample were 

 identified and the age structure analysis must be considered inconclusive. The results of the 

 food habits analysis indicate that the bottlenose dolphins stranded during 1990 had a similar 

 prey spectrum as in previous years. The analysis of environmental factors (sea surface and 

 air temperatures, salinity, and offshore transport) detected a statistically significant inverse 



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