Exposure assessment of the biotoxin domoic acid in California sea lions: Application of a bioenergetic model

Abstract

The biotoxin domoic acid (DA), produced by diatoms of the genus Pseudo-nitzschia, has caused massive California sea lion Zalophus californianus mortalities and live strandings along the California coast. Since quantifying the field DA dose that causes toxic effects in sea lions is logistically difficult, a bioenergetic model that uses age/sex-specific energy requirements was developed to estimate DA doses, assuming ingestion of 2 important vector species: anchovies Engraulis mordax and sardines Sardinops sagax. In this model, uncertainty and variability were incorporated by assigning sampling distributions to each model variable. Variables included: (1) vector energy density and assimilation efficiency of gross fish energy; (2) sea lion weight and energy requirements adjusted for energy expenditures associated with foraging, growth and reproduction; and (3) DA concentration in the vector species. Model outputs were analyzed relative to thresholds that cause adverse effects in other mammal species (1 and 2.71 mg DA kg-1 body weight). Based on DA concentrations measured in fish during a previous Pseudo-nitzschia bloom, consumption of anchovies versus sardines as 20 % of the sea lions' daily intake would result in a 4-fold increase in risk of non-lethal toxic effects. Across age classes, the median DA dose in pups (7 to 12 mo old) was twice that estimated for juveniles and was between 2 and 4 times greater than for adults. In DA dose estimates most of the variability resulted from the uncertainty associated with the energy density of the vector species and DA concentration in sardines rather than from the uncertainty associated with sea lions. Finally, we highlight the most relevant areas of research needed for determining a definitive risk of sea lion exposure to DA. © Inter-Research 2007.