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Dolphin Multiple Stressor Assessments

Co-producing a conceptual model to support assessments of cumulative effects from multiple stressors on Houston area dolphins under CERCLA and OPA

Natural Resource Damage Assessment (NRDA) decision makers will evaluate whether or not to pursue NRDA claims that include restoration of Houston area bottlenose dolphins potentially injured by releases of polychlorinated biphenyls (PCBs) and dioxins, but face data gaps on the cumulative effects of co-exposures. The project team seeks to develop conceptual models, statistical models, and analyses based on laboratory and field survey data to help managers conduct more targeted and specific NRDA pre-assessment evaluations under CERCLA (Comprehensive Environmental Response, Compensation, and Liability Act) and OPA (Oil Pollution Act). 

Lead Investigator: Ryan Takeshita, National Marine Mammal Foundation (

Natural Resource Manager: Michel Gielazyn, NOAA Office of Response & Restoration; Teresa Rowles, NOAA Office of Protected Resources

Project Team: Lori Schwacke, Marine Mammal Commission; Kristi Fazioli, Charted Marine Consulting in support of the Environmental Institute of Houston; Amie Lund, University of North Texas; Vanessa Mintzer, Galveston Bay Foundation; Aaron Roberts, University of North Texas; Amie Lund, University of North Texas; Irvin Schultz, NOAA Northwest Fisheries Science Center; Heidi Whitehead, Texas Marine Mammal Stranding Network; Ashley Barratclough, National Marine Mammal Foundation

Collaborators: Errol Ronje, NOAA National Marine Fisheries Service; Len Thomas, University of St. Andrews; Kevin Kirsch, NOAA Office of Response & Restoration 

Federal Program Officer/Point of Contact: Frank Parker (

Award Amount: $2,070,643

Award Period: October 2023 – September 2028

Why it matters: NOAA and their co-Trustees will evaluate whether or not to pursue NRDA claims for restoration of bottlenose dolphins in the Houston area that were potentially injured by releases of PCBs and dioxins. Addressing data gaps about how co-exposures may lead to cumulative effects and then incorporating that knowledge into the existing conceptual model(s) will benefit the NRDA decision-making process.

What the team is doing: The team will: 1) characterize exposure by analyzing blubber samples from previous biopsy surveys and compare the data to ranging patterns and across demographic groups; 2) evaluate population-level effects by conducting bi-annual surveys to inform spatial capture-mark-recapture analysis and compare population survival rates to other populations in the southeast U.S.; 3) investigate individual-level effects by collecting remote biopsy skin samples and analyze epigenetic markers to understand dolphin ages and health; and 4) describe the dose-response relationships of dioxins alone, PCBS alone, and both dioxins and PCBs together by conducting laboratory exposures with cell lines.

Expected outcome: The project team will co-produce conceptual models, statistical models, and analyses that can be updated based on additional data and assumptions that they or others may collect in the future. Decision makers will then be armed with information to design more specific and targeted studies for their particular cases and assessments, should claims for restoration of dolphins be pursued. Anyone conducting risk assessments of other potential stressors in the Houston area will have more context to effectively evaluate cumulative effects on marine mammals.