An unusual combination of factors -- including a high density of congregating fish, low flows, warm temperatures and a delayed upstream migration -- sparked a disease epidemic that led to the loss of more than 34,000 salmon and other fish in the Klamath River in 2002, according to a study released today by the U.S. Fish and Wildlife Service.
The study attributes the direct cause of death for most of the fish to an outbreak of two freshwater pathogens, Ich and columnaris. Both pathogens are commonly found in the Klamath River, so additional factors combined to stress the fish and increase their susceptibility to the pathogens. The report says those factors included:
in; - 1. The large size of the fall run of Chinook salmon returning to the Klamath River from the Pacific Ocean. The run was the eighth largest for the period from 1978 to 2002. in; - 1. High densities of fish in the lower river, which allowed the pathogen outbreaks to spread quickly. Large numbers of fish congregated in the lower river one to two weeks earlier than normal, but a lack of rainfall or freshwater pulses left the fish with no cues to begin their upstream migration. in; - 1. Relatively low flow in the lower Klamath River. Average monthly flows in August and September 2002 were the fifth lowest in the period from 1978 to 2002. in; - 1. Hot weather, which left water temperatures higher than optimum for salmon.Fish and Wildlife Service Director Steve Williams praised the scientists who prepared the report, which took about a year to complete and was the subject of a rigorous internal peer review.
