Evaluating the Effects of the Biotoxin Domoic Acid in California Sea Lions Via Computer Modeling Bay
Adriana C Bejarano, NOAA
12 Jan 2007
Exposure of California sea lions (CSL) to the phycotoxin domoic acid (DA) via ingestion of vector species (i.e., anchovies Engraulis mordax and sardines Sardinops sagax) has resulted in massive mortalities along the California coast. Models were developed, using currently available information, to assess the effects of DA on the CSL population. First, a probabilistic bioenergetic model that estimates age specific energy requirements was used to generate DA doses in individual CSLs. Later, model results were incorporated into an individual-based population model (IBM) to assess potential population level effects. Uncertainty and variability in the bioenergetic model were incorporated by assigning sampling distributions to each of the model parameters. Model outputs were analyzed relative to thresholds known to cause adverse effects in other mammal species (1 mg DA/Kg bw and 2.71 mg DA/Kg bw). Our model suggests that anchovies pose a greater risk of exposure to DA than sardines. A daily diet comprised of 20% anchovies would result in 4x the number of females affected, relative to a 1 mg DA/Kg threshold, than a 20% sardine diet. In addition, the model showed that regardless of the vector and amount of food ingested, the estimated 50th percentile of DA dose in sea lion pups is nearly double that predicted for juveniles and between three to six times greater than that of adult sea lions. An IBM model, adjusted for current population structure and growth rates, survivorship schedules and CSL sex/stage behavioral differences suggests different population trajectories resulting from several realistic model manipulations.