Klamath Falls Field Station
Understanding factors limiting the recruitment of endangered Lost River suckers into the adult spawning populations
From time before memory, The Klamath Tribes harvested c'waam (Lost River sucker) and qapdo (shortnose suckers) for their high quality meat and oil. For most of the 20th century thousands of fish were taken each year, but declines in fish populations in the early 1980s led the tribes to close their sucker fishery in 1986, two years before these species were listed as endangered by the U.S. Federal Government. Presently the tribes restrict their take to a single fish each year, collected for ceremonial purposes. Poor recruitment to the adult spawning populations is one of several reasons cited for the decline of Lost River and shortnose suckers. The U.S. Geological Survey and The Klamath Tribes are working together to restore c'waam and qapdo to their former abundance and determine the factors preventing recovery of these species.
Declining catch rates for juvenile suckers in Upper Klamath Lake in late summer each year indicate that first-year survival limits recruitment. However, it is not clear if the bottle neck preventing recruitment into adult populations of suckers occurs at the same life stage in other populations of suckers, such as those in Clear Lake Reservoir, in Modoc County, California. With the help of the U.S. Fish and Wildlife Service and student interns from The Klamath Tribes, USGS is working to identify the life stage or life stages in which survival of suckers in Clear Lake Reservoir is limited. Preliminary results from the 2011 pilot study indicate c'waam in this system may not survive to the juvenile life stage, whereas qapdo survival in this system may be limited in the juvenile life stage.
One hypothesis about the cause of poor recruitment in Upper Klamath Lake sucker populations is that cyanotoxins produced by algal species in the lake damage the livers of suckers and lead to eventual mortality. This hypothesis is supported by the detection of high levels of the hepatotoxin microcystin in Upper Klamath Lake during 2007 coincident with a high portion of suckers with liver damage. To test the plausibility of the hypothesis, USGS and The Klamath Tribes are initiating a study to determine if the concentrations of cyanotoxins found in Upper Klamath Lake can cause liver damage similar to what was observed for suckers caught in the wild. In the study, which is presently being conducted at The Klamath Tribe Research Hatchery, juvenile c'waam will be exposed to varying concentrations of microcystin through feeding experiments. Histological examination of liver and digestive tissues collected from fish at the end of the feeding trials will be used to determine if cyanotoxins are a potential cause of poor juvenile sucker health and survival.