Report on Estimate of Mortality
Report Number AFWO-01-03
In September 2002, a devastating fish die-off occurred in the lower Klamath River, prompting an investigation by the U.S. Fish and Wildlife Service (USFWS) and other agencies. This article aims to provide an overview of the die-off and highlight the significant presence of older fish from the Trinity River Hatchery among the casualties.
Summary of Findings: The USFWS report on the estimate of mortality revealed that a total of 34,056 observable fish died during the incident. The majority of the dead fish, approximately 98.4 percent, were adult anadromous salmonids. Out of the estimated 33,527 anadromous salmonids that succumbed, 97.1 percent were fall-run Chinook salmon, 1.8 percent were steelhead, and 1.0 percent were coho salmon. Only one coastal cutthroat was found dead during the investigation.
Significance of Trinity River Hatchery: The report highlighted that a significant proportion of the dead Chinook salmon were of hatchery origin, specifically from the Trinity River Hatchery. Approximately 12.7 percent of the Chinook salmon deaths were attributed to fish from this hatchery. After accounting for variable tagging and shed rates, the Klamath River Technical Advisory Team (KRTAT) estimated that 7,060 Chinook salmon (21.7 percent) were of hatchery origin.
Older Fish Affected: One notable finding was that the fish affected by the die-off were predominantly older fish. The report mentioned that almost all (greater than 99 percent) of the dead fish observed were adults or larger species of fish. This indicates that the mortality primarily impacted mature fish populations in the Klamath River.
Causes of Mortality: The investigation revealed that the majority of the recently dead fish exhibited outward signs of disease, including gill necrosis, bacterial growth, sores, bloody vents, and ulcerations. Pathological examinations confirmed that white spot disease and columnaris were the principal immediate causes of death.
Collaboration and Acknowledgments: The investigation and report were a collaborative effort involving the U.S. Fish and Wildlife Service, California Department of Fish and Game, Yurok Tribe, Hoopa Valley Tribe, and the Klamath River Technical Advisory Team. The report acknowledged the contributions and reviews provided by these organizations in the investigation and drafting of the report.
Conclusion: The fish die-off in the lower Klamath River in September 2002 had a significant impact on the adult anadromous salmonid population, particularly fall-run Chinook salmon. The presence of older fish from the Trinity River Hatchery among the casualties highlights the vulnerability of hatchery-origin fish during such events. The findings of this report will aid trustees in making informed decisions regarding the affected fisheries resources and related assets under their authority.
Note: The information in this article is sourced from the provided document.
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