Pollutants in pelagic predators

The key objective of this project is to document the change in concentration of organochlorine contaminants in individuals within and among three shark species over a large size range, and model bioaccumulation curves for each species.

Although interest in elasmobranch toxicology has increased, the field lags far behind that for most other taxa, including mammals, birds and amphibians. Little information is available regarding baseline data for many species and the factors that may influence how these animals accumulate organochlorine contaminants. Furthermore, even less is known about the effects of these contaminants on elasmobranch physiology. One challenge to determining the potential impact of these organic contaminants on elasmobranchs is the lack of information available about the dynamics of accumulation in larger, pelagic elasmobranchs; data which is necessary for monitoring and risk assessment. Understanding the dynamics of contaminant bioaccumulation is important for modelling species contaminant trajectories and identifying the age classes that have the highest exposure to contaminants, which will ultimately be important for examining the effects they have on elasmobranch species.

In the United States, southern California is one of the largest DDT (dichlorodiphenyltrichloroethane) hotspots in the world due to historic dumping in the region by large manufacturing companies. To this day, high levels of DDT and other organic contaminants such as PCBs (polychlorinated biphenyls) can be measured in animals from nearly every trophic level in the region. Elasmobranch toxicology research in southern California has increased in recent years and has produced some sentinel papers on maternal offloading of contaminants and on bioaccumulation in stingrays. Despite this growth in knowledge, we still do not have a good grasp on bioaccumulation in sharks, especially large pelagics that are relatively long-lived and feed higher on the food chain. Previous work has demonstrated that differences in accumulation may be related to trophic position, although this has not yet been formally tested. Therefore, the goal of the present study is to address some of these knowledge gaps by examining contaminant accumulation over the whole available range of age classes for several species of pelagic sharks. The data provided by this study will be important for understanding the extent of bioaccumulation of organic contaminants in elasmobranch species, which may be used in risk assessment and for management consideration.

• Measure organic contaminants in the liver tissue of three study species (the blue, shortfin mako and common thresher sharks) across several age classes.
• Compare concentrations of organochlorine contaminants among the three species at each major life history point (i.e., young of the year, juvenile, sub-adult and adult stages) and compare contaminant bioaccumulation trajectories among species that occupy different trophic levels.
• Determine the contribution of the major contaminant group (i.e., DDT, PCBs, other chlorinated pesticides) to the total contaminant load and compare levels to other studies that have documented negative effects of the specific chemical of interest to make inferences on potential effects that could be occurring in the study species.
• Indicate the major chemicals in need of further exploration and suggest future directions of study to examine the effects of these contaminants in elasmobranchs.