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Western Fisheries Science News, February 2016 | Issue 4.2

February 26, 2016

Are Colonial Waterbirds Inhibiting the Recovery of Suckers in the Upper Klamath River Basin?

Researchers scan for sucker PIT tags on a mixed nesting colony of American white pelicans and double-crested cormorants at Clear Lake Reservoir in the Clear Lake National Wildlife Refuge. Photo courtesy of USGS.

In an effort to better understand the decline of the Endangered Species Act (ESA)-listed Lost River and Shortnose suckers, researchers at Real Time Research, Inc. and the U.S. Geological Survey (USGS) Klamath Falls Field Station are employing a technique that has not been used in the Klamath Basin before.  In a new study, researchers estimated predation impacts by nesting fish-eating waterbirds utilizing Passive Integrated Transponder (PIT) tag data.  Although several types of birds nest in the Basin, and are presumed to forage on suckers, researchers specifically concentrated efforts on American white pelicans (pelicans) and double-crested cormorants (cormorants) nesting at mixed-species colonies on Clear Lake Reservoir, CA and Upper Klamath Lake, OR during 2009-2015.  These large birds are thought to cause the greatest foraging impact on adult-sized suckers.

For the study, PIT tags were implanted in Lost River and shortnose suckers.  PIT tags allow specific information to be attached to individual fish, including species, size, age-class (adult, juvenile) and release location. These PIT tags also allow researchers to evaluate sucker movements, growth, survival, and other demographic parameters, and have been the backbone of a long-term USGS monitoring program for the endangered suckers in the Klamath Basin.

When the suckers are consumed by waterbirds, some of the PIT tags are deposited in nesting colonies by either regurgitation or defecation.  Electronic recovery of PIT tags on waterbird colonies has proven to be helpful in identifying which individual bird colonies pose the greatest threat to fish survival and estimate avian predation rates. Predation rates estimated in the study are known to be minimum estimates, primarily because the study could not account for the unknown proportion of tags from consumed fish that were not deposited on a colony and were thus unavailable to be detected by the researchers.

Researchers found that predation impacts varied by sucker species, size, age-class, bird colony location, and year, demonstrating that predator-prey interactions were dynamic. Adult suckers as large as 730 mm fork length were consumed by pelicans, and all but the largest suckers in Upper Klamath Lake were susceptible to predation. Although sample sizes for PIT-tagged juvenile suckers were limited, the study provided some evidence that juvenile-sized suckers were more susceptible to avian predation than adult-sized suckers. Results also indicated that predation by pelicans and cormorants may be a factor limiting recovery of ESA-listed suckers in Clear Lake. Survival of adult suckers in Upper Klamath Lake does not appear to be limited substantially by avian predation, as minimum predation rates were less than two percent and overall survival of adult suckers is high.  In contrast, avian predation may be a significant source of mortality for adult Lost River and Shortnose suckers in Clear Lake, where estimates of minimum predation rates were as high as five percent. Furthermore, spawning runs into Willow Creek, the lone spawning tributary for suckers in Clear Lake, are limited when flows are low in the creek as a result of drought conditions.  These conditions could make suckers more susceptible to avian predation.

Additional research is needed to measure predator-specific predation rates, estimate PIT tag deposition probabilities on bird colonies, better understand biotic and abiotic factors that regulate sucker susceptibility to bird predation, and to better estimate predation rates on juvenile suckers in both water bodies, especially Clear Lake.

The study was funded by Bureau of Reclamation with support from U.S. Fish and Wildlife Service, and the Klamath Sucker Recovery Implementation Team.


Hewitt, D.A., and B.S. Hayes. 2013. Monitoring of adult Lost River and shortnose suckers in Clear Lake Reservoir, California, 2008–2010: U.S. Geological Survey Open-File Report 2013-1301, 18 p.

Hewitt, D.A., E.C. Janney, B.S. Hayes, and A.C. Harris. 2015. Status and trends of adult Lost River (Deltistes luxatus) and shortnose (Chasmistes brevirostris) sucker populations in Upper Klamath Lake, Oregon, 2014: U.S. Geological Survey Open-File Report 2015-1189, 36 p.

Evans, A., Q. Payton, B. Cramer, K. Collis, D. Hewitt, and D.D. Roby. 2015. Colonial waterbird predation on Lost River and shortnose suckers based on recoveries of passive integrated transponder tags. Final Technical Report to Bureau of Reclamation, Klamath Basin Area Office, Klamath Falls, Oregon. 22 p.

Newsletter Author - Debra Becker



USGS Hosts Science Exchange with Tribes:  On February 22-23, the WFRC Columbia River Research Laboratory hosted a science exchange with members from the Spokane Tribe of Indians, Confederated Tribes of the Colville Reservation, and Coeur d’Alene Tribe of Indians. Participants discussed habitat and fish assessments, food webs and predation in Columbia River reservoirs, fish passage strategies, and innovative technologies. The USGS and tribes have been discussing science and technologies that could support salmon reintroduction in currently blocked areas of the Upper Columbia River.

Scientist Presents New Dam Removal Science Website to the USGS Community of Data Integration:  On February 10th, Research ecologist Jeff Duda gave an online presentation to the USGS Community of Data Integration (CDI) on the Dam Removal Information Portal (DRIP), a USGS product developed with CDI funding. Arising from a dam removal synthesis project at the USGS John Wesley Powell Center, DRIP is a dynamic, map-based database of dam removal scientific studies that is linked with other USGS and partner cyber infrastructure. The provisional USGS website is available at


USGS Researcher Selected to Receive Presidential Early Career Award:  Maureen Purcell, research microbiologist, has been selected to receive a Presidential Early Career Award for Scientists and Engineers, the highest honor bestowed by the United States Government on science and engineering professionals in the early stages of their independent research careers. Purcell was selected on many criteria, including her research on the molecular basis of the innate immune response of fish to pathogens or vaccines and the roles of both genetics and the environment in the process. Her work has gained global recognition through a series of highly-cited publications in journals that have significantly advanced our understanding of how finfish respond to microbial threats. The winners will receive their awards at a Washington, D.C. ceremony this spring.

USGS Scientist Recognized as Member of the Water Prize Competition Center Team to Win “Newcomer of the Year Award” from As described in the winter 2015-2016 edition of the Bureau of Reclamation’s (BOR) Water Prize Competition Knowledge Stream issue, USGS scientist Patrick Connolly and fellow team members were recognized with a “Newcomer of the Year” award. Connolly has been playing a role in shaping prize challenges, initiated by funding gained by the BOR, to design prize competitions for solutions to a number of outstanding questions that impact fisheries resources. Visit to see more about the Water Prize Competition Center.

In the News

During the week of February 15, results of a scientific reports manu-script by USGS scientist Jason Romine and co-authors was featured in various news media outlets, including Science Daily, Bay Journal, Nature World News,, Shark Year Magazine, SciFeeds, and Wynpr Baltimore public radio. The manuscript challenges a 2007 study claiming that shark declines led to rising population of cownose rays, which was thought to be responsible for the collapse of oyster and shellfish industries along the Atlantic coast.


New Publication Brings into Question Current Management of Sharks, Skates, and Commercial Bivalve Stocks in the Atlantic: Understanding the linkages between predators and prey, as well as and potential trophic cascades, is important for managing species. In the northwest Atlantic Ocean, the depletion of large coastal sharks was thought to trigger a trophic cascade whereby predation release resulted in increased cownose ray abundance, which then caused increased predation on and subsequent collapse of commercial bivalve stocks. These claims were used to justify the development of a predator-control fishery for cownose rays, the "Save the Bay, Eat a Ray" fishery, to reduce predation on commercial bivalves. In a recently release manuscript by USGS scientist Jason Romine and colleagues from Florida State University, NOAA National Marine Fisheries Service, and the Virginia Institute of Marine Science, researchers found that upon reexamination coastal sharks did not coincide with purported rapid increases in cownose ray abundance and increases in cownose ray abundance did not coincide with declines in commercial bivalves. Cownose rays have extremely low reproductive potential and the purported increases of cownose rays are unrealistic based on their life history. Researchers found that incorrect hypotheses may negatively influence conservation and management decisions.

Grubbs, R.D., J.K. Carlson, J.G. Romine, T.H. Curtis, W.D. McElroy, C.T. McCandless, C.F. Cotton, and J.A. Musick. 2016. Critical assessment and remifications of a purported marine trophic cascade. Scientific Reports 6, Article number: 20970.

New USGS Report Provides Science Support for Missouri River Sturgeon: The pallid sturgeon is an endangered fish endemic to the Missouri and Mississippi rivers and the lower parts of larger tributaries. Concerns under a biological opinion indicate that U.S. Army Corps of Engineers operations of the Missouri River were likely to jeopardize its existence, with primary stressors such as habitat alternation related to changes in flow regime and channel form. Implementation of fish, wildlife, and habitat restoration activities on the Missouri River has been guided by principles of adaptive management since adoption in 2000. The USGS and colleagues from Oregon State University, Mississippi State University, U.S. Army Corps of Engineers, and U.S. Fish and Wildlife Service recently completed a report in cooperation with Missouri River Recovery Program that provides a compilation and assessment of available scientific literature, databases, and models that will be used as the foundation of understanding of how pallid sturgeon population dynamics are linked to management actions in the Missouri River. Note: WFRC scientist Mike Parsley actively participated in the project up until his retirement in 2014. 

Jacobson, R.B., M.J. Parsley, M.L. Annis, M.E. Colvin, T.L. Welker, and D.A. James. 2015. Science information to support Missouri River Scaphirhynchus albus (pallid sturgeon) effects analysis: U.S. Geological Survey Open-File Report 2015-1226, 78 p.