Background

The recent listing of the Columbia River Distinct Population Segment of bull trout identified one of the major threats to the species as fragmentation resulting from dams on overwintering habitats of migratory subpopulations (Federal Register, 1998).  A migratory subgroup in the Tucannon River apparently utilizes the mainstem Snake River for adult rearing on a seasonal basis.  Their occurrence in the hydropower system has been verified by a few incidental observations during sampling in Lower Monumental Pool (Buchanan et al. 1997 citing Ward), and in the adult passage facilities at Lower Monumental and Little Goose dams in the early 1990s (Kleist, in litt. 1993).  Based on fish counting schedules outlined in COE (1997), no attempts at adult fish enumerations are made at the Lower Monumental or Little Goose fish counting windows from Nov. 1 through March 31. Unfortunately, this scheduled abandonment of fish counting activities coincides with adult bull trout movements into larger mainstem systems for adult rearing and foraging as indicated in other Columbia Basin subpopulations (Elle 1995; Faler and Bair 1992; Martin et al. 1995; Theisfeld et al. 1996; Underwood et al. 1995).  As a result, it is unknown if the existing fishways at the lower Snake River dams are suitable for bull trout passage, or if migratory fish originating from the Tucannon River attempt to pass these facilities on a regular basis.  

The potential for bull trout movements throughout the migratory corridor is high, but from the standpoint of future delisting and requirements set forth in the FCRPS Biological Opinion (USFWS, 2000) the determination of temporal and spatial distribution in the mainstem is crucial in developing recovery actions, estimating "take", and successful consultation on system improvement actions.   This project will help meet Reasonable and Prudent Measures, and Conservation Recommendations associated with the Lower Snake River dams in the FCRPS Biological Opinion.

Rieman and McIntyre (1993) describe unimpeded migratory corridors as important habitats to the persistence and interaction of local populations.  They also indicate that disruption and/or modification of migratory corridors can increase stress, reduce growth and survival, and potentially result in the loss of migratory life-history types in a subpopulation. With these factors in mind, the primary question to be answered is: Does the existing hydropower system on the Lower Snake River limit the capabilities of Tucannon River bull trout to complete their migratory behavior, or are the current hydropower operations compatible with recovery and conservation of the species?  The secondary goal of the project is to examine the movements and spatial/temporal distribution of migratory bull trout within the Tucannon River and to determine the proportion of migratory fish that leave the Tucannon River to overwinter.  The bull trout stock status in the Tucannon River is considered healthy by the Washington Department of Fish and Wildlife (WDFW 1998), but little is known about their migrations in the Tucannon and Snake river subbasins.  Underwood et al. (1995) conducted a radio telemetry study of adult bull trout within the Tucannon River, but the tracking data were limited, with only a few fish tagged and only one winter of tracking.  As a result, it did not provide a complete assessment of the migrations and movements of bull trout-especially in the mainstem Snake River.  Transmitters used in this study were reaching the end of their life expectancy at the time the tagged fish were outmigrating toward the Snake River.  Contact was lost with all fish near the mouth of the Tucannon River.  

This study will focus on the migratory component of bull trout in the Tucannon River and describe their use of the Snake River Reservoirs in both spatial and temporal terms.


Objectives

Our objectives are to:

1.  Determine the spatial distribution, migration timing, and movements of adult migratory bull trout in the Tucannon and Snake rivers.

2.  Determine bull trout use and passage efficiency in fishways at Lower Snake River dams.

3.  Estimate frequency of bull trout fall back at Lower Snake River dams.

4.  Determine if bull trout losses result from movements out of Lower Monumental Pool.

5.  Summarize and distribute the information to others.


The proposed study will test these null hypotheses:

  Obj. 1.  Ho-Overwintering migratory bull trout from the Tucannon River range widely in the Lower Snake River.

Ha-Migratory bull trout from the Tucannon River overwinter specifically in the Lower Tucannon River and Lower Monumental Pool.

  Obj. 2.  Ho-Adult bull trout overwintering in the Snake River move through the fishways at the Lower Snake River dams.

Ha-Adult bull trout overwintering in the Snake River do not move through the fishways at the Lower Snake River dams.

  Obj. 3.  Ho-Adult bull trout overwintering in the Snake River fall back through the dams into downstream reservoirs.

Ha-Adult bull trout overwintering in the Snake River do not fall back through the dams into reservoirs downstream.

  Obj. 4.  Ho-Adult bull trout that fall back through Lower Monumental Dam or pass upstream through the Little Goose fishway freely return to the Tucannon River the following spring to spawn.

Ha-Adult bull trout that fall back through Lower Monumental Dam or pass upstream through the Little Goose fishway do not return to the Tucannon River, are lost to the population, and contribute to "take" resulting from FCRPS operations.


Approach

Critical Assumptions: The primary assumption associated with the study is that the movements of radio-tagged bull trout are not different from the movements of other bull trout in the subgroup. This assumption is critical to the project as a whole.  The use of long life transmitters and tagging well before spawning or major migrations should reduce the effects of tagging on fish behavior.  Martin et al.  (1995) found that surgically implanted dummy transmitters did not affect fish survival, growth, or gonad development in rainbow trout held in captivity.  Similar transmitters have been used in other bull trout studies in recent years without indications of adverse behavioral affects (Elle 1995 ,  Faler and Blair 1992, Underwood et al.  1995, Jon Germond, ODFW, pers. comm.).

Objectives 1, 2 and 4 have critical assumptions, in part, associated with each of those objectives. In order to determine distribution in the Snake River (Objective 1) and passage efficiency (Objective 2), we must assume that a portion of our group of radio-tagged bull trout will enter the Snake River and at least attempt to pass through a fish ladder in the Lower Snake River.  Likewise, in order to estimate the extent of losses in Objective 4, there must be some movement (upstream or downstream) of radio-tagged bull trout out of Lower Monumental Pool and we also assume that radio transmission will be adequate to track bull trout movements throughout the reservoirs.  

We also assume that we can tag enough migratory bull trout to provide meaningful tracking results in the Tucannon and Snake rivers.  Trapping data from the past 2 years have shown that over 100 taggable sized bull trout have been captured at the Tucannon Hatchery weir during the spring migration.

Sampling: The approach of the study is to use radio-telemetry to monitor the movements of trout as they emigrate to the Snake River to rear in the winter.  Up to forty adult and sub-adult bull trout per year would be captured and tagged in the Tucannon River during the fall outmigration using a downstream migrant weir and/or hook and line sampling.

Each captured bull trout will be measured, weighed, marked with a  PIT tag, and released at the site of capture.  Those fish of appropriate size (> 50 times transmitter weight in air) will be surgically implanted with a 236 day life expectancy radio-tags (Objectives 1-4).   Surgical procedures will generally follow those used by Faler et al. (1988) and Faler and Bair (1992). We are now focusing out tagging efforts in fall and winter to increase the chances of monitoring outmigrants into the Snake River.

Radio-tags for this study will be obtained from Lotek Engineering.  The Lotek tags are 3 volt, coded tags in models NTC-6-2 (4.5 g, 236 day life expectancy at 7s burst rate).  With these transmitters, we could safely radio tag bull trout as small as 225 g, or approximately 1/2 lb.  Specific frequencies and codes to be used will be coordinated through the University of Idaho so that existing fixed receiver stations in the Snake River will have the capability of logging radio-tagged bull trout as they pass those sites.  Critical operating sites for this study will include 4 fixed stations at the upstream and downstream ends of the adult fishways at Lower Monumental and Little Goose dams.  These fixed site data loggers will be in operation throughout the winter and spring to record bull trout movements through fish ladders at the dams (Objective 2).  In addition, a fixed site will be operated near the mouth of the Tucannon River to identify timing of movements out of the Tucannon subbasin and into the mainstem Snake River.  Another fixed site will likely be established and operated periodically at the Tucannon Fish Hatchery to record timing of fish movement in the upper Tucannon River.  Radio-tagged fish locations will also be monitored approximately weekly throughout the year in the Tucannon River from shore, and biweekly by boat, shore, or aircraft between November and May (Objective 1).  Individual fish locations will be recorded by river kilometer, and in relation to distance and direction to known landmarks.

Analysis: Winter distribution of bull trout will be delineated by the furthermost upstream and downstream fish locations observed in the study period and by month.  Distribution will be described monthly as a river reach encompassed by river kilometer identifiers at the upper and lower limits (Objective 1).  

Data retrieved from fixed station data loggers will be examined to determine if bull trout move through the fish ladders at either dam.  If so, passage rates will be calculated from the time of entry to time of exiting.   If sufficient numbers of radio tagged fish move through the fishways, the variability of the data set will be examined to determine generalities in those rates and data outliers, if they exist.  Bull trout passage rates will be compared to salmon and steelhead passage rates already determined at those dams by Bjornn and Peery (1992) to detect differences, if any, in passage rates between species (Objective 2).

Bull trout that fall back through spill gates, navigation locks, or turbine intakes will not likely be detected at the fishway fixed stations.  We will use distributional data from tailrace receivers (operated by the Univ. of Idaho) boat, shore or aircraft locations to determine the occurrence and frequency of fall back through the dams (Objective 3).

Data sets from individual bull trout that move out of Lower Monumental Pool will be examined to detect the return of those fish to the Tucannon River, and passing the hatchery weir, the following spring.  A loss determination will be inferred if those fish do not return through a dam, and into Lower Monumental Pool by May, the following year (Objective 4).  It is possible that none of the radio-tagged bull trout will leave Lower Monumental Pool, and if so, an estimate of loss/take may not be possible.

The possibility of tag failure or signal loss resulting from excessive depth may also cause problems with data interpretation.  These situations will need examination on a case by case basis to consider their data applicability to the project objectives.