In response to the Council’s December 8, 2015 request, the ISRP reviewed the Spokane Tribe of Indians’ Fiscal Year 2016 proposed “Lake Roosevelt Northern Pike Suppression Plan.” This proposed suppression effort is a scope change for the ongoing Lake Roosevelt Fisheries Evaluation Program (Data Collection) project (#1994-043-00). The proposed effort is intended to reduce the proliferation of northern pike in Lake Roosevelt through immediate suppression actions guided by studies evaluating the proposed techniques. This proposal is based on baseline data from a pilot study on the northern pike population in Lake Roosevelt (reported within the proposal), which indicated a recent marked increase in abundance of northern pike. Northern pike are voracious predators that threaten native species and non-native game fishes, and they have the potential to move downstream in the Columbia River to possibly impact the recovery of ESA listed salmon.
The proposed northern pike suppression project for Lake Roosevelt is closely related to work by the Kalispel Tribe in Box Canyon Reservoir, Pend Oreille Subbasin, Washington (projects #1997-004-00 and #2007-149-00). The ISRP concluded that the Kalispel Tribe’s effort to suppress the northern pike population in Box Canyon Reservoir was justified. The proponents of the Box Canyon Reservoir suppression effort are applying gillnetting techniques to target spawning populations in shallow water. The proponents of the Box Canyon effort concluded from a pilot study that “intensively netting northern pike in sloughs and backwaters from ice off through the spring freshet could drastically reduce the abundance of northern pike in Box Canyon Reservoir.” They set an objective to reduce northern pike abundance by 85% in Box Canyon Reservoir, which is likely to require more annual effort (i.e., more gillnetting during the spawning period and/or more gillnetting at other times of the year) than was conducted during the pilot study.
ISRP Recommendation: Response Requested
This proposal is consistent with the Box Canyon Reservoir northern pike suppression effort. However, further development of several elements of this proposal would improve its scientific credibility:
(1) The proposal should include clearly state hypotheses about northern pike suppression that will be tested. For several activities proposed – including suppression, telemetry, and index netting – there is no indication as to how these activities are expected to yield an understanding of the effectiveness of the proposed northern pike suppression program. (See Comments, 1. Sound science principles [i.e., methods],#4below for examples of testable hypotheses.)
(2) The proponents should explain why they believe their proposed removal effort and monitoring will be adequate to control or suppress the northern pike population and measure resulting benefits. The concern about northern pike introduction in the Columbia River Basin needs to be addressed, both at the sources and downriver. From a source in Lonepine Reservoir in the Little Bitterroot system where northern pike were introduced in the 1950s, northern pike have subsequently spread downstream in the Flathead River, into the Clark Fork and Lake Pend Oreille, and into the Pend Oreille River, Box Canyon Reservoir, and into Lake Roosevelt. Northern pike are probably well-established in all of these waters. The expansion of northern pike is a systemwide problem with a continual source of fish upriver from Lake Roosevelt. This reality is not discussed or dealt with in the proposal. Therefore, there is reason to be skeptical that the proposed suppression effort will be sufficient to reduce the long-term abundance of northern pike in Lake Roosevelt to a level where meaningful benefits can be observed. It is requested that evidence or rationale be provided by the proponents addressing their ability to control or suppress the northern pike population. Additionally, they should provide details on the methods used to measure benefits, the amount of effort required, and the specifics of the monitoring program.
(3) The proposal should include clearly defined quantitative objectives with targets (i.e., outcomes, endpoints) over specified time periods. Only a vague statement describing the desired outcome is presented in the proposal (see Comments, 3. Clearly defined objectives and outcomesbelow). Effective adaptive management requires development and use of quantitative objectives in proposals and management plans.
(4) The proposal calls for “Spring Pike Index Netting” to occur annually, but there is no mention as to how the resulting monitoring data will be used to evaluate the suppression program. Data analyses should be linked to assessment of hypotheses (#1 above) and quantifiable objectives (#3 above).
(5) There is no mention of a component to evaluate the extent of removal that may occur from the proposed effort. The proposal should address what could be done to estimate the annual exploitation rate (i.e., annual fishing mortality) of northern pike and the relationships to abundance, length structure, age structure, total mortality, and other indices of northern pike population structure and dynamics. Have mark-recapture studies in conjunction with suppression efforts been considered?
(6) The description of the telemetry component is insufficient for the reviewers to make judgments. More detail is needed. Additional information should address what the proponents want to learn from the telemetry study and how this information will be used to improve the northern pike suppression efforts?
(7) There is a need to assess the extent of by-catch and its potential impacts on native and desired non-native fish populations in the reservoir. Although by-catch will be greatly reduced by netting northern pike at spawning time, it is not clear that this limited netting approach over a short time and relatively small area will be adequate to reduce northern pike abundance in Lake Roosevelt. Gillnetting at other times and locations, which may be necessary, would likely yield more by-catch mortality. There is a need for a clearly stated quantitative objective regarding maximum acceptable by-catch and how the objective has been determined and will be assessed.
(8) An important task in the near future is to assess the impacts of northern pike on focal species. For example, a bioenergetics model could be coupled with population estimates to approximate the effects of pike suppression compared with no suppression where the predator population is allowed to grow. These issues should be discussed in the proposal and the contributions that the Lake Roosevelt northern pike suppression project may make should be stated.