This is a complex project that was clarified considerably by the response and modified proposal. Statement of the hypotheses was useful and demonstrated how big a problem the study attempts to tackle and also suggests that too much is being attempted at once. It would seem better to focus on one or a subset of the hypotheses in order to have more likelihood of successful explanations and management approaches. The sponsors invoke work at the Colorado River as a template. The Colorado River model may be a good start, but the Columbia may be more complex.

The first part of the response indicates the sponsors do not seem to have grasped the "overarching" point the ISRP made about structural changes in the Columbia River reservoirs arising from milfoil. This aquatic weed may foster the development of fish communities that include predators and competitors with juvenile salmon because, for example, it provides shelter for non-salmonids. The sponsors are keen on using stable isotope analysis (SIA) to investigate how milfoil decreases or increases energy flow in the reservoirs and speculate a change will effect salmon production. However, the aforementioned structural modification could confound their study and merits attention.

The answers to ISRP's questions 1 to 4 showed some advancement in approaches but the project needs focusing on specific topics, as outlined below.

ISRP question 1:

The ISRP requested that the sponsors provide a focused and strategic approach with a set of well-developed hypotheses rather than a synoptic study as described.

The sponsors now raise a number of null hypotheses or topics to be investigated (see below for list of null hypotheses given the response).

Topic 1, dealing with milfoil and stable isotope analysis, is tractable and should be funded, although ISRP remains concerned about the interaction with the structural effects of the plant (see above).

Work on topics 2, 3, 4, and 5 should not be funded. The study dealing with competition between fish species (topic 2) is very difficult to conduct without parallel investigations to determine if food is limiting. Numbers 3, 4, and 5 deal with major topics that are not tractable with the scope and timeframe of the project.

In another topic, the sponsors also intended to sample and characterize the isotope signatures of the lower trophic levels using a probabilistic habitat based sampling design during different times of the year. The ISRP did not support this objective as it is a reversion to a synoptic approach.

ISRP question 2 - the ISRP requested more details and description of the specific food webs, and these were provided. A specific task is now included that will allow for the sampling of tissue and stomach contents of multiple white sturgeon life stages, common carp, juvenile American shad, northern pikeminnow, and smallmouth bass. The food web investigations are therefore now supportable as long as the sponsors do not invoke competition as a rationale for conducting them (see above). The ISRP is happy to see that empirical feeding data (fish stomach contents) will be obtained.

ISRP question 3 - the ISRP remains concerned about the manager's ability to use stable isotope analysis data in their day-to-day work. If stable isotope analysis analyses are going to be used every few years to assess the ecosystems, researchers will have to do the work, not managers. This is apparently what is being done in the Colorado River, and it is reasonable to assume it would be done this way in the Columbia River Basin. Considerable technology transfer will therefore be required before the stable isotope analysis methods could be handed off to managers.

ISRP question 4 - Information on where the stable isotope analyses will be determined and the capability of the laboratory staff was provided satisfactorily.

List of research topics, in response to ISRP's question 1:

# 1: Despite the fact that Eurasian watermilfoil is now abundant in shallow water habitats and likely constitutes a large proportion of the plant biomass in Bonneville Reservoir, the production of this aquatic plant does not contribute significantly to the food web.

#2: Common carp are competitors with white sturgeon and utilize similar energetic pathways.

#3: The Asian clam is a significant component of the food web in Bonneville Reservoir and contributes energetic resources to white sturgeon.

#4: The Northern pikeminnow and smallmouth bass are benefiting from the altered energy flow caused by the establishment of invasive species in the mainstem Columbia River, namely the American shad.

#5: Established invasive species constitute a major perturbation to the historic food web in the mainstem Columbia River.