Factors limiting survival of juvenile endangered suckers.
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.
In 2007, high levels of the hepatotoxin microcystin were found in Upper Klamath Lake while a high portion of preserved suckers collected during that time had liver damage. These observations led to the hypothesis that cyanotoxins produced by algal species in the lake damage the livers of suckers and lead to eventual mortality. To test the plausibility of this hypothesis, USGS and The Klamath Tribes conducted 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. During this study juvenile Lost River suckers were exposed to varying concentrations of microcystin-LR through feeding experiments. Histological examination of liver and digestive tissues collected from fish at the end of the feeding trials indicated that there was no liver damage. Furthermore, microcystin concentrations found in the tissues of exposed suckers was generally less than 1% of the amount of microcystin fed to the suckers. Consequently, we determined that microcystin-LR was unlikely to be a primary cause for the mortality of juvenile Lost River suckers in Upper Klamath Lake but it might indirectly affect sucker survival.
Another hypothesis about the cause of poor recruitment of young suckers into adult spawning populations is that multiple stressors contribute to mortality. With the help of The Klamath Tribes we estimated survival in conjunction with temperature and parasite loads. Ichthyobodo spp. is a common parasite that infests fish skin and gills and is known to be present in Upper Klamath Lake and has been found in fish in both the federal and tribal fish-rearing facilities. Our results suggest that survival of Lost River suckers with a natural infection of Ichthyobodo spp. was significantly impacted by temperature.
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Factors limiting survival of juvenile endangered suckers.
Sources/Usage: Public Domain.USGS, Klamath, and Modoc researchers are studying the effects of the algal toxin microcystin on juvenile c’waam (Lost River sucker) at the Klamath Tribe Research Hatchery. Credit: USGS, Western Fisheries Research Center. (Public domain.) 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.
In 2007, high levels of the hepatotoxin microcystin were found in Upper Klamath Lake while a high portion of preserved suckers collected during that time had liver damage. These observations led to the hypothesis that cyanotoxins produced by algal species in the lake damage the livers of suckers and lead to eventual mortality. To test the plausibility of this hypothesis, USGS and The Klamath Tribes conducted 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. During this study juvenile Lost River suckers were exposed to varying concentrations of microcystin-LR through feeding experiments. Histological examination of liver and digestive tissues collected from fish at the end of the feeding trials indicated that there was no liver damage. Furthermore, microcystin concentrations found in the tissues of exposed suckers was generally less than 1% of the amount of microcystin fed to the suckers. Consequently, we determined that microcystin-LR was unlikely to be a primary cause for the mortality of juvenile Lost River suckers in Upper Klamath Lake but it might indirectly affect sucker survival.
Another hypothesis about the cause of poor recruitment of young suckers into adult spawning populations is that multiple stressors contribute to mortality. With the help of The Klamath Tribes we estimated survival in conjunction with temperature and parasite loads. Ichthyobodo spp. is a common parasite that infests fish skin and gills and is known to be present in Upper Klamath Lake and has been found in fish in both the federal and tribal fish-rearing facilities. Our results suggest that survival of Lost River suckers with a natural infection of Ichthyobodo spp. was significantly impacted by temperature.
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