Effects of Environmental Contaminants
By Randall Wells
 |
| Dolphins accumulate contaminants from the fish they eat. |
Dolphin health continues to be a primary focus of our research program, especially in relation to effects of environmental contaminants. Previous work with the Sarasota dolphins suggests that these animals are exposed to moderate levels of some chemical contaminants (including organochlorines such as DDT metabolites and PCBs), facilitating the investigation of sub-lethal effects of these chemicals on dolphin health and reproduction. Such research requires the examination and collection of samples from individuals of known age, sex, and reproductive history for measurement of contaminant residues, health assessment and reproductive activity. This kind of research has been identified by the International Whaling Commission and NOAA Fisheries as requisite to understanding the effects of contaminants, and identifying biomarkers of the contaminants. To address these issues, and to begin to understand the dynamics of these fat-soluble chemicals in dolphins seasonally and inter-annually, we have been conducting dolphin capture, sample, and release programs in Sarasota Bay, through the support of Dolphin Quest, NOAA Fisheries, and Disney. Each of the 5-25 dolphins examined and sampled during a given session is involved in about 20 different projects. Typically 40 to 100 or more scientists, veterinarians, students, and dolphin handlers participate in the work over a three to five day sampling period at three times during the year.
Dolphins are encircled with a net, and are brought aboard a specially designed veterinary examination vessel. Body condition is evaluated (weight, length, girth, ultrasonic measurement of blubber thickness). The animals are given a physical exam, and blood, milk, blubber, urine, fecal, and microbiological samples are collected. Diagnostic ultrasound provides information on health and reproductive condition. Well-known mothers know ages of most dolphins from documentation of their birth; unknown ages are determined from growth layer groups in a tooth. Organochlorine concentrations in blubber, milk, and blood are examined relative to age, sex, body condition, birth order, and health parameters, including immune system function. Possible effects on reproductive success are examined through measurement of reproductive hormone concentrations, tracking of paternity patterns as determined from genetic samples, and by tracking individual female calving success through their reproductive lifespan.
Identifying the most appropriate analytical laboratories and securing funding for these analyses has taken a number of years, but tremendous progress is being made now that these issues have been largely resolved. Samples are being analyzed by several different laboratories, through the support of NOAA Fisheries, International Whaling Commission, and the Conservation Medicine Center of Chicago. Analyses by the University of Utah (W. Jarman), University of Barcelona (A. Borrell), and NOS (G. Mitchum) have yielded preliminary results that were presented in an invited talk in November 2002 at the Annual Conference of the Society for Enviromental Toxicology and Chemistry, in Salt Lake City. Initial findings indicate the accumulation of organochlorine contaminant residues in dolphin tissues at levels that exceed those of concern for human health.
High concentrations in first-time mothers correlate with high first-born calf mortality. Concentrations in females decline with lactation, a process known as “depuration.” Apparent relationships for males between increases in concentrations of contaminants with age, and declining testosterone concentrations and shorter lifespan are being examined, but conclusive cause-effect relationships have not yet been demonstrated. Continuing analyses of new samples and analyses of archived samples will be conducted by the National Institute of Standards and Technology (J. Kucklick), and the University of Guelph (D. Muir/M. Houde). We will be able to begin to look at the relationships between specific congeners of the contaminants relative to health and reproduction. Studies are also underway to look at the effects of inorganic chemicals such as mercury and selenium on dolphin health (T. O’Hara/V. Woshner). In combination, long-term observational monitoring and periodic biological sampling provide a powerful, non-lethal approach to understanding the correlations of contaminant concentrations and health or reproductive parameters in coastal dolphins, thereby providing critical information for hazard and risk assessment in marine mammals.