Local or MSRT Comments: See Washington guidance

It is surprising how little is known about the lake, considering it contains several listed salmonids as well as a sockeye pen-rearing program. The need to gather more data from Lake Wenatchee to understand trophic processes justifies further research. This proposal essentially examines whether juvenile sockeye and Chinook rearing in the lake are limited by top-down (predator) or bottom-up (nutrients and plankton) factors. Phase I examines the role of predators -- bull trout and pikeminnow; Phase II examines nutrient limitation and the potential for lake fertilization to boost salmonid productivity.

The response to the ISRP's questions suggest that justification of Phase I is adequately supported. It does seem possible that predator populations are consuming enough juvenile sockeye and Chinook to have a significant impact on the populations. Determining whether or not predators are consuming these fish incidentally to supplement their regular prey organisms or are targeting them seems worth exploring.

To address Phase I will require measurements of abundance of predators along with information on the components of their stomach contents and their rates of digestion. According to the Response, information is lacking other than observations that "Large congregations of predators, for example, have been observed at net pens and the mouth of rivers during times of hatchery releases and out migrations of naturally produced fish into the lake" (Response page 2). Sponsors plan on using tangle nets to collect predators. The ISRP appreciates that sponsors are designing a system to avoid harm to captured listed species. The tangle nets they plan on using may not be effective, however. They could seriously miss the abundance of predators like northern pikeminnows, and could be counter productive if the collections are not sufficient to estimate the important parameters.

The justification for Phase II, the nutrient limitation work, is weaker. To really understand whether Lake Wenatchee will benefit from a fertilization program it will be necessary to conduct a fairly thorough examination of the lake's physical limnology. This will entail understanding the timing and pattern of stratification and the influence of the incoming tributaries on the lake's circulation pathways. A worst-case scenario (and we're not implying it would occur here) would be that added nutrients would be quickly transported in surface layers to the lake's outlet without ever reaching the target phyto- and zooplankton. Unless the circulation patterns are well understood, the effectiveness of lake fertilization can be compromised.

In addition to the physical limnology, developing a thorough bioenergetics model requires measurements of the key components of the chemical and biological makeup of the lake. Information is needed to develop the estimates of interactive effects among fish species in the lake. While the proposal makes reference to bioenergetic models in this context, it is not clear that the references cited for spring Chinook and sockeye salmon adequately take into account the zooplankton that might be utilized by other fish species in the lake, for example, juvenile bull trout or northern pikeminnow and others. It is not clear how the zooplankton samples will be expanded to abundance estimates for the lake as a whole or for a volume of water occupied by a given mass of Chinook or sockeye. There needs to be an explicit bioenergetics model and the plans for populating the model with Lake Wenatchee data as part of the work that is recommended for funding.

Therefore, the ISRP suggests that Phase I is fundable, with funding for Phase II contingent on Phase I findings and a complete review of what is known about Lake Wenatchee's physical limnology.

This is an ambitious lake ecosystem study whose management value is not established by the technical background. Does this study replicate other investigations of trophic and food web structure of other Pacific Northwest lakes that could be used to make management recommendations for Lake Wenatchee? Are all of the components necessary to decide which management actions to pursue?

The proposal falls short of providing sufficient information to conclude that the study, and information, is necessary. First, the background and technical section asserts that recreational angling for kokanee has decreased in recent years, and they attribute this to potential bull trout predation. But no quantitative support for this assertion is provided. Consequently there is a lack of evidence that a problem actually exists – either for the kokanee recreational fishery or for production of juvenile spring Chinook or bull trout. Second, the sponsors do not adequately justify the potential causes of decreased salmonid production – either lack of nutrients in the lake or predation by bull trout or pike minnow. Thirdly, the description of the management actions that would be employed to remedy the problem is overly vague – presumably either a lake fertilization program or a predator removal program.

In a response the proposal needs to provide evidence that kokanee, juvenile salmon, and bull trout production in Lake Wenatchee are well below the expected production. There should be a review of literature available on 1) the Lake Wenatchee ecosystem, 2) other oligotrophic lakes in the Pacific Northwest, and 3) how lake fertilization and predator control programs have affected the abundance and productivity of target species. A lot is already known that has application here. For example, Mullan's (1986) review of sockeye includes an evaluation and recommendation on fertilization. Finally, the response should identify the minimal information that would be needed to decide whether these management interventions were necessary and appropriate. The work elements and tasks would then be to collect this essential information.

Additional Comments:

When proposing to fertilize a body of water the size of Lake Wenatchee they need to consider the water quality objectives established on the lower river. There may be TMDL limits for water quality parameters in the lower river and fertilizing the lake may create problems remaining in compliance. Assurances from water quality agencies that a lake fertilization program will not compromise water quality objectives further downstream should be given; otherwise, the nutrient limitation investigations will not lead to management actions.

It was unclear what exactly the role of the cooperators (Drs. Beauchamp, Bennett, and Black) would be. There doesn't seem to be any budget requests related to their involvement, but the brief summary on page 21 of the narrative suggests that they will have major responsibilities in this project. They are all highly qualified, but their level of effort here was not specified.