T4 AM Endangered Species and Environmental Contaminants: Status of the Science (Part 1)
Tuesday, 15 November 2005: 8:00 AM - 11:40 AM in Ballroom 4

(SPR-1117-852993) Modeling how contaminant effects on somatic growth may impact endangered Chinook salmon populations.

Spromberg, Julann¹, Meador, James¹, ¹ NOAA Fisheries, Seattle, WA, USA

ABSTRACT- Many compounds inhibit somatic growth in fish. Size has been linked to age-specific survival rates, age at reproductive maturity, fecundity, and spawning success. Therefore, sublethal reductions in somatic growth may affect life history characteristics, including age-specific survival and reproductive traits. Reductions in the somatic growth rate of salmon fry and smolts are believed to result in increased sizedependent mortality during migration, smoltification, and overwintering. A matrix population model for endangered Chinook salmon ( Oncorhynchus tshawytscha ) was adapted to incorporate a size-dependent survival rate for a three-month interval during migration to the ocean. Two sets of models investigate how changes in the size distribution of juvenile Chinook altered the population growth rate and the number of returning adults. The first set looked at the impacts of growth reduction due to longterm sublethal exposure to PAHs. Changes in the size distribution of the population were based on a laboratory experiment in which juvenile Chinook were exposed to PAHs in their food over a 53-day period. The survival rate distributions were calculated from the treatment size distributions and were used to calculate first year survival (S1). Projections were run for 20 years in 1-year increments. S1 was recalculated annually using a survival value selected from the calculated survival distribution. The projections were repeated 5000 times and the returning adult abundance mean, standard deviation, and 95% confidence intervals were calculated. While some PAH treatments did not produce a change in mean size, differences in the standard deviation and resulting survival distributions occurred for all treatments. While the mean number of spawners did not differ greatly, the lower 95% confidence interval value was lower than the control, increasing the probability of lower returns. A second set of models to be conducted simulates the indirect effects on growth of pesticide exposures resulting from feeding suppression.

Key words: sublethal effects, endangered species, Chinook salmon, growth inhibition