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A Synthesis of Existing Data for Resident Fishes in the Snoqualmie River Above Snoqualmie Falls

Category: Fish/Shellfish Research and Management - Fish/Shellfish Research

Date Published: June 2008

Number of Pages: 78

Author(s): Nathanael C. Overman

EXECUTIVE SUMMARY:

This synthesis is a summary of the fisheries research conducted on trout and mountain whitefish Prosopium williamsoni in the Snoqualmie River, with emphasis on resident cutthroat trout Oncorhynchus clarki, rainbow trout Oncorhynchus mykiss, and eastern brook trout Salvelinus fontinalis above Snoqualmie Falls and sea-run cutthroat trout below the Falls. Specifically, it is intended to provide a comprehensive summary of the studies and data that will be useful in implementing the Snoqualmie River Game Fish Enhancement Plan (SRGFEP), and to identify data gaps for ten primary research topics identified in the Plan: relative trout abundance, trout distribution, trout movement, trout reproductive life history, age and growth studies, creel census, background environmental data monitoring, habitat surveys and mapping, habitat enhancement, and public education.

Fisheries and environmental data relevant to these topics have been collected periodically by various entities; however, rigorous field studies of the fish resources in the Snoqualmie River are limited. In 1985, a comprehensive management plan for wild trout was assembled for the Snoqualmie River above Snoqualmie Falls that summarized most of the relevant fisheries data from 1969-1984 (Pfeifer 1985). Since then, data have been collected both opportunistically and as part of larger studies, and this synthesis is intended to be as inclusive as possible.

Results of this review indicate that data gaps are present for almost all the research tasks identified in the Plan, although the extent to which research has already been conducted for each task varies from non-existent to comprehensive. Tasks with the fewest data gaps are the habitat surveys and mapping and background environmental data portions of the Plan. Most of this information has been collected or is currently being monitored, and allocating significant resources to these tasks is not warranted. Tasks with the most glaring data gaps include behavioral data such as instream movement and spawning behavior, and a rigorous age and growth analysis for each salmonid species including mountain whitefish. Trout densities have been estimated periodically for various reaches in all three forks, however species-specific abundance estimates for each fork are still needed. Existing creel survey data is outdated; updated creel information is needed to evaluate the state of the fishery, its potential, and regulations affecting angler harvest and effort. Finally, studies focused specifically on sea-run cutthroat trout in the Snoqualmie River below the falls are largely absent.

Relative Trout Abundance – Density and abundance estimates are outdated and surveys did not always differentiate among trout species. New species-specific density estimates should be obtained using more rigorous mark-recapture techniques.

Trout Distribution – Trout distribution and species composition needs to be reassessed in each fork and in the major tributaries to the forks using data collected with a variety of fisheries techniques.

Trout Movement – Radiotagging efforts are needed to assess whether trout exhibit extensive instream or among-fork movements including seasonal transitions to summer feeding stations, overwintering areas, and spawning sites.

Trout Reproductive Life History – Spawning surveys, radiotagging, and redd capping are needed to assess current spawning distribution, habitat preference, spawning duration, and egg/alevin incubation periods.

Age and Growth Studies – Rigorous age and growth analyses are needed for each salmonid species including mountain whitefish.

Creel Census – New creel surveys are needed to assess the current status of the fishery and to evaluate regulations affecting angler harvest and effort.

Background Environmental Data Monitoring – Measurements of stream temperature, turbidity, discharge, and other water quality parameters are currently recorded at monitoring stations operated by various agencies.

Habitat Surveys and Mapping – Extensive habitat surveys and mapping have already been conducted. The detail and extent of these surveys is beyond the scope of this project and allocating effort to this aspect of the Plan is largely unwarranted.

Habitat Enhancement – Very little habitat enhancement has been conducted on the Snoqualmie River. Enhancement recommendations should be provided to Puget Sound Energy and other government entities upon completion of the Plan.

Public Education – As the project nears completion, a pamphlet should be developed and posted on the WDFW website promoting the fishery resource in the Snoqualmie River. The potential for constructing kiosks or placing signs at strategic locations in the watershed should also be evaluated. The final report should be made available to the public and results presented at local angling clubs.

Trophic Interactions – Although the SRGFEP does not specifically outline plans to study trophic interactions, some of this data can be collected opportunistically while addressing other research questions. Diet data in particular is very sparse and should be collected during this study.

Sea-run Cutthroat Trout – Quantitative information for coastal cutthroat trout in the Snoqualmie River below the falls is minimal. Although the majority of the time and effort in this project will be directed above Snoqualmie Falls, some effort should be allocated to collection and analysis of sea-run cutthroat trout in the river below the falls. At a minimum, snorkeling should be conducted to characterize relative abundance and general distribution of sea-run cutthroat trout.

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