Health Assessment Modeling and Effects of Environmental Contaminants
By Ailsa Hall, Phd and Randall Wells, Phd

        Man has had a large impact on the health of the marine ecosystem.  Over-fishing, pollution, oil exploration and shipping activities, to name a few, have indirectly affected marine mammals throughout the world.  Many of these impacts have been to affect the ‘health’ of the individuals in the population so that their reproductive capacity or survival is depressed. 

    In the light of these global impacts the purpose of this study is to investigate the health of the population of Sarasota Bay bottlenose dolphins and find out how this has changed over time.  In support of this goal, health assessment projects were conducted in February and June of 2004, resulting in sampling and evaluation of 31 dolphins.  This work supported more than 20 different research projects.  Because we also have a great deal of knowledge about the structure and dynamics of the Sarasota Bay population we are investigating how we can integrate information on the health of the individuals that make up the population (such as from clinical chemistry information and exposure to contaminants) and their relationship to changes in abundance, fecundity and survival.  Bottlenose dolphins are important sentinel species; with this in mind, our program published a paper in EcoHealth this year that describes initial efforts to develop a system for evaluating the health of dolphin populations from evaluation of clinical blood parameters.  This study also forms part of a wider investigation of different populations of dolphins from New Jersey to Florida. 

    So far we have found that certain clinical blood chemistry measures fluctuate significantly with age, sex and seasonally.  Clearly we need to take these changes into account when we look at decadal changes that might be a function of longer-term changes in the quality of the Sarasota Bay environment.

    We have also constructed an ‘individual based model’ to help provide a particular type of risk assessment framework for the Sarasota Bay population.  We suspect that when calves are exposed to high levels of environmental contaminants such as polychlorinated biphenyls (PCBs) in milk from their mothers their first year survival probability is significantly reduced.  From data collected in Sarasota Bay on levels of organochlorine environmental contaminants such as PCBs in the blubber of females (Figure 1), females appear to transfer PCBs and related contaminants to their calves through milk.  Their first calf gets a particularly heavy dose, and the survival of the first calf is particularly low.  Our model then allows us to test what effects various exposure and response scenarios will have on the potential population growth rate.  In this way we have been able to highlight where future research efforts should be directed in order to say with some certainty what effect such contaminants are likely to be having on the long-term dynamics of the Sarasota Bay community of bottlenose dolphins.