Tissue toxicants and prespawn mortality in Willamette River Chinook salmon

In some Pacific salmon Oncorhynchus spp . populations, many adults die after reaching freshwater spawning sites but prior to spawning, a phenomenon known as prespawn mortality (PSM). Causal factors for PSM are often uncertain, but pathogens, warm water temperature, and environmental toxicants have been implicated in several studies. In this two-year project, we examined the relationship between toxicants and PSM in a threatened population of spring-run Chinook salmon O. tshawytscha (Walbaum) in the Willamette River, Oregon. Muscle and skin samples from 63 female carcasses were screened for ~125 potential toxicants, including trace elements, pesticides, and organohalogens. Mean concentrations for five toxicants selected for their known adverse effects on salmonids were: 4.3 ( SD = 2.0) ng/g cadmium, 72.9 (122.7) ng/g nickel, 10.0 (9.0) ng/g lead, 12.7 (8.6) ng/g polychlorinated biphenyls (PCBs), and 17.6 (10.3) ng/g DDT (an organochlorine pesticide). Using generalized linear models, we found no statistical differences in toxicants concentrations between successful ( n = 37, 58.7%) and unsuccessful ( n = 26, 41.3%) female spawners. We conclude that selected contaminants did not provoke acute toxicity in Willamette River Chinook salmon. It remains unknown whether sub-lethal or chronic toxicant effects on adult salmon physiology or behavior have affected the fitness of this threatened population.