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Preface:
This report is a result of 5 years of focused research on persistent organic pollutants (POPs) in livers of freshly dead sea otters sampled between 2000 and 2005. Over 130 POPs were examined, including pesticides, butyltins, PBDEs, PAHs and PCBs. The goal of the research was to determine concentrations of the various pollutants in sea otter livers, and to examine the resulting data for patterns with respect to each sea otter's age, sex, stranding location, proximity to major sources of runoff, sewage and centers of dense human populations along the coast. We also are looking for patterns between having elevated liver POP concentrations and specific causes of death.

ABSTRACT

Here we present the results of a multi-year epidemiological study focused on investigating demographic, environmental and spatial risk factors for exposure of sea otters to persistent organic pollutants (POPs) along coastal California. An additional objective was to examine the associations between elevated liver POP burdens and major primary and contributing causes of sea otter death. In addition to being a federally protected threatened species, California’s southern sea otters (Enhydra lutris nereis) also have the potential to serve as ideal upper trophic level sentinels of nearshore pollution by anthropogenic waste, including chemicals and pathogens; Sea otters possess 4 unique biological traits that distinguish them from all other marine mammals in California: 1) They have comparatively small home ranges, 2) They have a comparatively high resting metabolic rate, requiring consumption of high volumes of marine foods, 3) They prey heavily on filter-feeding invertebrates, which can concentrate chemical and biological pollutants when present in local water and sediments, and 4) They live and feed along the immediate shoreline, which places them in close contact with plumes of anthropogenic wastes entering the ocean. Thus, southern sea otters are an ideal species to monitor to assess long-term trends in POP deposition to the local environment, as well as to monitor the environmental effects of planned and ongoing mitigation and control measures. In the present study, samples from 227 wild sea otters stranding between 2000 and 2005 along the California coast were tested for the presence of most major classes of POPs, including PCBs, PBDEs, PAHs, organochlorine pesticides and organotins. Potential contributors to the risk of POP exposure that were considered in the various statistical models included sea otter sex, age class, nutritional condition and stranding location, as well as the proximity of each stranding location to major points of coastal freshwater runoff, municipal wastewater discharge or dense coastal human populations. Of 138 compounds examined, the vast majority (117) were detected in livers of stranded, freshly dead southern sea otters. DDTs had the highest mean liver concentrations of all major contaminant groups, followed by PCBs and PBDEs. The POP analyte found at the highest levels in liver was p,p’ DDE, with a mean of 614 ng/g wet weight, followed by PCB 153

(30.3 ng/g wet weight) and PCB 138 (24.6 ng/g wet weight). When overall population means were compared between this and prior studies, hepatic concentrations of DDTs appear to have declined significantly in southern sea otter livers since 1970. Sea otter age class, sex, and nutritional condition were significant risk factors for POP detection in sea otter livers. . In general, immature sea otters had the highest liver concentrations of POPs, emaciated animals had higher POP levels than animals with abundant body fat, and the effect of gender varied, with females having higher liver POP concentrations than males for some POPs that were significantly affected by gender. With regard to sea otter mortality, the top 3 most important findings at necropsy were considered in all statistical models, because some common disease processes, including trauma and infectious disease are often present concurrently in southern sea otters. When fully stratified for age, gender and stranding location, no significant positive or negative disease correlations were found for total butyltins, PBDEs, PCBs, DDTs or any other pollutant groups, when examined with respect to the top 3 most important lesions present at necropsy. However, liver concentrations of some POP analytes were significantly correlated with the presence of specific infectious diseases, as well as traumatic death, including C1­dibenzothiopene, PCB 056, chlordane-cis, oxychlordane and PBDE 028. Striking differences were found with regard to associations between increased liver concentrations of particular POPs and sea otter death due to bacteria, acanthocephalans and protozoa. However, when all causes of infectious disease were pooled for analysis, no summed or individual POPs were found to correlate with an increased or decreased risk of sea otter death due to infectious disease, when other risk factors such as sea otter sex, age, stranding area and nutritional condition were accounted for in multivariate models. Based on these preliminary analyses, several demographic, spatial and environmental risk factors, including nutritional condition, stranding location and sea otter proximity to moderate to high coastal discharges of surface runoff and municipal wastewater were found to be as or even more important predictive factors of sea otter death due to infectious or traumatic disease than was POP detection at high concentrations in liver. This is the first study to screen tissues from a large number of freshly dead southern sea otters selected without bias to the stranding location or cause of death, and to fully stratify the resulting data for potential demographic, spatial and environmental risk factors that could confound the perceived risk of POP exposure for sea otter death due to infectious disease. Studies are currently in progress to re-examine these data in the context of each otter’s primary cause of death and to more directly compare our research findings with those from other marine mammal studies.

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