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FEEDBACK: More Details, Clarifications On Dworhak Reservoir Nutrient Supplementation
Posted on Friday, March 09, 2012 (PST)

FEEDBACK: More Details, Clarifications On Dworhak Reservoir Nutrient Supplementation

 

-- From Ed Schriever, Chief of Fisheries, Idaho Department of Fish and Game

 

An article (CBB, Jan. 20, 2012, “Corps Dworshak Nutrient Supplementation Study Aims To Boost Kokanee, Listed Bull Trout http://www.cbbulletin.com/415679.aspx) about the Dworshak Nutrient Supplementation Project was published in a recent issue of the CBB and was followed by a response by Mike Faler (fisheries biologist) of Orofino (CBB, Jan. 27, 2012, “Feedback: Dworshak Nutrient Supplementation Study” http://www.cbbulletin.com/415834.aspx)

 

Mr. Faler pointed out what he believed to be omissions, discrepancies, and inconsistencies in the article. We would like to provide some clarification regarding his assertions.

 

Mr. Faler claimed that this project was not generated as a result of public input.  I can tell you from personal experience that if not for the personal championing of the concept and potential merits of nutrient supplementation by a member of the local community working with the Orofino Chamber of Commerce the project may have never happened.

 

At that time there was growing local public concern related to loss of recreational use at Dworshak Reservoir as a result of summer-time reservoir drawdowns being implemented as part of the FCRPS Biological Opinion. Idaho Fish and Game and the U.S. Army Corps of Engineers investigated the nutrient enhancement concept as a way to improve the reservoir ecosystem -- and ultimately improve recreational fishing -- and determined it was worth further evaluation. Pre-project planning meetings were held with Dr. John Stockner (a nutrient supplementation expert), state, tribal, and federal agency staff and representatives of local government and Idaho congressional staff. Numerous presentations were made to civic groups in the community prior to implementation.

 

The agencies decided to initiate a pilot project to evaluate this management strategy because of the potential benefits to the ecological function of the reservoir and the public interest in enhancing recreation. 

 

Mr. Faler is correct that kokanee exhibit density-dependent growth. However, historical declines in nutrient levels and the growing imbalance in the nitrogen to phosphorus ratio in Dworshak Reservoir have altered the food web, resulting in less food being available for kokanee. Prior to nutrient supplementation, periodically high kokanee densities coupled with limited food supplies resulted in high numbers of small fish that were not desirable to anglers. 

 

Kokanee densities in 2006 (pre-enhancement) and 2010 were similarly high. However, as evidence of the benefit of nutrient supplementation, the biomass of kokanee was nearly twice as high in 2010 as it was in 2006. These larger and heavier fish were a result of improvements in the food web and produced a more desirable fishery.

 

The original article notes that the reservoir has twice produced state record smallmouth bass. As Mr. Faler accurately notes, both of these records were both produced prior to the start of nutrient supplementation. We have not contended that the project was responsible for these trophy fish. The intent of the statement was to point out that Dworshak Reservoir supports more than just a popular kokanee fishery. Other species, such as smallmouth bass, may benefit from the project because of improvements to the reservoir food web that it will likely provide.

 

Mr. Faler cites the frequency of blue-green algae blooms in recent years and disputes our assertion that blue-green blooms are not caused by nutrient supplementation. While blue-green algae continued to persist in Dworshak Reservoir during periods when it was treated, we are confident that the project did not cause the observed blooms. For one, blooms of toxic blue-green algae were observed in seven out of eight years for which we have pre-treatment sample data. 

 

Further, neither the percent composition nor amount of toxic blue-green algae observed in samples taken during the project were ever higher than values reported from pre-treatment sample data, and in many cases were lower. Finally, blue-green blooms observed during the treatment period were observed in untreated arms (experimental controls areas) of the reservoir as well as treated areas.

 

Before the project was initiated, the COE contracted Dr. John Stockner to perform an assessment of Dworshak Reservoir based on an analysis of historical and contemporary water sample data that had been collected. In this assessment, Dr. Stockner identified a dominance of nitrogen fixing blue-green algae during the summer and fall. Since these tend to be large colonial-type algae that are generally inedible to zooplankton, they were considered a dead end in the food web.

 

One of the goals of the project has been to reduce to dominance of these large, nitrogen fixing blue-green algae to improve the efficiency of the food web. The project accomplishes this by adding relatively small amounts of nitrogen, to match the available phosphorus, to help the food web produce more favorable types of algae.

 

In short, based on the best available science, it is our expectation that implementation of a long-term nutrient addition program for Dworshak Reservoir will concurrently reduce the frequency of blue-green algae blooms, improve the reservoir ecology and provide better fishing.

 

Finally, Mr. Faler cites an online poll in the Lewiston Tribune as an indicator of the level of public support for this project. It is widely accepted that online polls are not an effective method for representatively gauging public support. There certainly are members of the public who have voiced concern about this project, but there are also many who support it. Recently, the USEPA reviewed the project design, implementation and monitoring results while contemplating issuance of a NPDES permit. The EPA heard the concerns voiced by the public related to the project during their NEPA analysis and recently issued a NPDES permit for the project. 

 

Results from the Dworshak Nutrient Supplementation Project have been encouraging to date. However, further evaluation will be conducted before determining whether nutrient supplementation should become a long-term implementation action. We are using a science-based approach to adequately make this determination.

 

Ed Schriever

Chief of Fisheries

Idaho Department of Fish and Game

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