Acute effects of suspended sediment angularity on juvenile coho salmon (Oncorhynchus kisutch)

To determine the roles of suspended sediment angularity and concentration a s contributors to stress and mortality in salmonids, we exposed juvenile co ho salmon (Oncorhynchus kisutch) to anthropogenically derived "extremely an gular" and "round" silicate sediments over a range of concentrations in 96- h experiments. Stress responses (e.g., decreased leukocrit) were elicited b y exposure to both sediment shapes when concentrations were >40 g.L-1, corr esponding to the minimum concentration at which physical gill damage was ob served. Extremely angular sediments also caused stress responses (e.g., ele vated hematocrit, decreased leukocrit) at concentrations <41 g.L-1. However , we found no difference between sediment shapes in causing mortality at an y sediment concentration. Further, mortalities were not observed until conc entrations were about 100 g.L-1, a value that is about an order of magnitud e greater than high natural concentrations in salmonid rivers. Natural fluv ial suspended sediments cause fish stress and mortality at much lower conce ntrations than we found with our anthropogenically derived suspended sedime nts.