In response to the Northwest Power and Conservation Council’s June 3, 2014 request, the ISRP reviewed a revised proposal for the Colville Confederated Tribes’ (CCT) project Lake Roosevelt Burbot Population Assessment (#2008-115-00). As described in the revised proposal, “the goal of the project is to achieve a stable, harvestable Burbot population in Lake Roosevelt. The primary objective of this project is to provide technical advice to the Lake Roosevelt Co-Managers [CCT, Washington Department of Fish and Wildlife, and Spokane Tribe of Indians] regarding management alternatives so that they can develop realistic fishery targets and appropriate implementation strategies. Stock assessment data will be used to estimate current population harvest potential, evaluate alternative management scenarios, and assess recruitment variability.”
This is a follow-up to the ISRP’s review and Council’s recommendation in the Resident Fish, Data Management, and Regional Coordination Category Review (ISRP 2012-6, pages 79 - 81). In that review, the ISRP recommended that the project met scientific review criteria in part: “The full proposal is not yet justified. Deliverable 1 should proceed. Previous and ongoing burbot data collection in Lake Roosevelt from WDFW Fall Walleye Index Netting (FWIN) should be fully examined and analyzed to determine if it is adequate for evaluating the status of burbot before exerting significant additional sampling effort in the lake. Evaluation based on Deliverable 1 should be used to design field sampling efforts, if needed, beyond existing efforts as a means to meet project goals. The ISRP should review a subsequent revised proposal that builds on results from Deliverable 1. The design should consider other ISRP comments noted below [provided in the full ISRP memo].”
The Council subsequently recommended “Implement Objective 1, deliverable 1 only through completion and not beyond FY2017 (Analysis of Fall Walleye Index Netting Bycatch Data). Sponsor to submit revised proposal based on this analysis for ISRP/Council for review and recommendation prior to additional assessment efforts in Lake Roosevelt.”
ISRP Recommendation: Meets scientific review criteria in part (qualified)
The proposal meets scientific review criteria in part; Deliverable 2 is not recommended until the feasibility of that deliverable can be demonstrated in a pilot project and until scenarios are developed to demonstrate how the proposed collection of new information could change the management of the fishery.
The recent analysis of FWIN data by Bennett and Steinhorst (2014) demonstrates that the existing FWIN program data can be used to detect year-to-year changes in relative abundance of burbot and to identify strong and weak year classes in a general way. It also provides estimates of age composition and length-at-age, although changes in these metrics over time may not be readily detectable unless the change is large. Thus, the sponsors should be able to detect trends in recruitment and provide basic data needed to monitor the population for the current modest fishery (typically <500 fish per year) for this large reservoir. Now that a comprehensive analysis of the FWIN data has been completed, it appears that relatively little additional effort would be needed to use these data to inform harvest management. Monitoring and full utilization of burbot bycatch in the FWIN program should continue; any burbot accidentally killed in the process of FWIN sampling should be sampled for age determination to aid in assessing year class strengths.
The basis for instituting more intensive field collections and stock assessment of this fishery, as outlined in the proposal, is less clear. The stated goal of this project is to liberalize fishing regulations for burbot if it is determined that the population can support greater harvest. Current regulations limit the daily harvest to five burbot, and setlines (multiple hooks) are not allowed. The fishery is open year round. These regulations already seem quite liberal compared with regulations elsewhere, including Alaska, especially given the health warning for potential consumers by the Washington Department of Health. Acquiring more data may not be particularly useful, necessary, or cost effective given the apparent limited interest in the fishery. Population estimates may not be needed to manage this fishery as trend data currently provided by the FWIN may be adequate. Not all fisheries can or need to be monitored intensively (e.g., Johannes 1998), especially if the fishery is small and of limited interest.
It was not clear to the ISRP how new information, beyond that obtained from FWIN, would be used to change burbot management in Lake Roosevelt. How much would the management of the burbot fishery improve if the sponsors gained the additional data? Would the additional data actually make a difference given the limited nature of the fishery? For example, the major field sampling effort proposed to examine selectivity (bias) of the FWIN gillnets has not been adequately justified in terms of how it would contribute to achieving the overarching management goal. The sponsors should also show how the additional data and FAMS analysis would better inform different harvest scenarios. The proposal does not describe any alternative harvest strategies for burbot. Broader social and ecological aspects of the harvest are not well described. Is it realistic to increase this fishery given that it is primarily a winter fishery? Is it prudent to increase this fishery given that burbot are generally a species of concern in the lower 48 states? Is it even desirable to expand this fishery given the health warning released by the Washington Department of Health for children and pregnant women that may consume burbot? In short, the goal of this project to potentially liberalize harvest regulations (e.g., increase daily bag limit beyond five fish) may not be warranted.
The sponsor’s concern over non-representative sampling of the small, young fish comes from the Bennett and Steinhorst (2014) analysis. The shortage of age two and younger fish in samples is hypothesized to be a result of limitations of the FWIN survey. To better assess the relative abundance of young fish, the sponsors would need to develop or test monitoring methods different than FWIN, specifically a bottom trawl capable of catching burbot representatively at ages 2, 3, and 4. These representative catch data could then be used to develop a scaling factor to correct any size bias in the FWIN data. Other factors may be clouding the current sampling results. For example, what if age 3 fish are migrants? The bottom trawl may help clarify these issues if it can representatively sample the key age groups. Are the sponsors also planning to use data for other non-target species captured with their proposed methods to better understand species composition in Lake Roosevelt?
Since it is not clear to the ISRP that more information is justified at the current level of the fishery, the proposed expansion of field monitoring requires additional justification. Is obtaining the identified information on younger-aged fish feasible and cost effective? Several sampling methods are identified including trawls, cod pots, and trammel nets, but no information is provided regarding the likely effectiveness of these methods, especially in Lake Roosevelt. The proposal does not describe efforts and successes using these and other methods elsewhere, in and beyond the Columbia River Basin. For example, mark-recapture experiments of burbot have not been effective in Canada (Neufeld 2008). Under these circumstances, it would be prudent to start by testing the effectiveness of new methods at a pilot level, one that is considerably less intensive than proposed. A full-blown sampling program should not be undertaken until some significant and potentially useful insights and catch rates as well as a feasible path forward have been demonstrated in a pilot study.
The ISRP also questions the feasibility of obtaining adequate data for the FAMS model, especially a measure of total recruitment in the reservoir.
Given the limited nature of the fishery and the unproven methods for effective sampling of younger burbot, Deliverable No. 2 (FWIN data that are corrected for size and age selectivity) is not recommended at this time. The ISRP suggests a focused, scaled-back field investigation until sampling methods are proven to be effective and the prospects for obtaining the needed data for FAMS modeling are much clearer.