Yukon River Chum Salmon Freshwater Ecology

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Yukon River Chum Salmon Freshwater Ecology and
Environmental Influences On Their Survival:
Ongoing research and analyzes (continued)

Methods

The first step taken in the project was to characterize the study areas. Stream habitat measurements (e.g. water velocity, substrate composition) were taken along transects. The study sites were then mapped using surveying equipment. These maps detail the stream channel, both full bank and low water flow, and major features (e.g. beaver dams, weirs). Benchmarks were established along the study area to facilitate mapping of the study area and spawning locations (redds).


Habitat measurements along a transect in Hodgin’s Slough (left). Field personnel use a theodolite to map in redd locations in Bluff Cabin Slough (right). Click on images for larger view.

Two weirs have been established each year at both Hodgin’s Slough (July –September) and Bluff Cabin Slough (September – November), defining the lower and upper boundaries of each study area. Weirs are operated on a continual basis allowing free passage of fish either upstream or downstream while maintaining a count of all fish within the study area. Chum salmon are processed as they enter the study area for the first time. Mideye-hypural length, mideye-fork length, maximum depth, weight, sex and condition are recorded and a genetic sample is taken. A Peterson disk tag, with a unique color/number combination, is affixed to allow identification. Otolith and vertebrate samples are taken from carcasses, for aging purposes. Foot surveys are conducted on a regular basis to provide an independent estimate of the number of fish in the area and retrieve carcasses.



The lower weirs at the Hodgin’s slough study site (top left) and Bluff Cabin Slough site (top right). Measuring the depth of a chum salmon (bottom left). A male chum salmon is ready to be released after processing (bottom right). The Peterson disk tag under the dorsal fin is used for identification. Click on images for larger view.

Tracking the number and movement of female chum salmon is an important aspect of the study. By knowing the number of females in the study area, a fecundity/length relationship can be used to estimate potential egg deposition (PED). Females are tracked, and spawning locations (redds) are mapped using a theodolite. These redd locations are then used to create a spawning distribution for the area. Redd locations are characterized in terms of habitat (e.g. water velocity, substrate composition, and intergravel water temperature).

During spring, emigrating smolts are captured using fyke nets. Wings are attached to the fyke nets to increase channel coverage and are extended or retracted to respond to flow changes. The Hodgin’s Slough site requires high-water submersible funnel nets during high-water events. Traps are checked on a regular basis and species are identified, counted, and immediately released.



During low flows, 100% of the stream channel can be covered (top left). At increased flow levels and debris loads, the wings must be shortened (top right). During high water events at the Hodgin’s Slough site, submersible funnel nets are used (bottom left). These high water traps are accessed using small inflatable boats (bottom right). Click on images for larger view.

Trap efficiency is calculated by releasing known numbers of marked chum smolt upstream of the trap. The numbers of smolt leaving the study area are compared with the PED estimate from the previous year to produce an estimate of egg-to-smolt survival rates within the study areas.

Comparison of marked to unmarked chum
salmon smolt. Bismarck Brown is used to produce the mark seen above.

Click on image for larger view.

Marked and unmarked chum salmon smolt comparison.

One of our main focuses to date at the study sites has been to refine and standardize methodologies. During 1997 and 1998, a hydraulic redd pump was used to estimate intergravel egg and alevin survival rates and densities. A further evolution of this research began in 1999 with the initiation of a new sub-study.

This sub-study is entitled “Quantification of upwelling as a determinant of spawning site selection and quality for Yukon River chum salmon”. Mini-piezometers (stand pipes) have been systematically deployed along transects in both summer-run and fall-run chum salmon spawning areas. Piezometers allow us to measure vertical hydraulic gradient (VHG, the pressure difference between intergravel and surface waters), substrate permeability, and subsurface water velocity. In addition, we take measure dissolved oxygen (DO), conductivity, and temperature within each piezometer. These data are allowing us to refine our characterization of spawning habitat at both sites.


The project began using piezometers in 1999, in an effort to determine which, if any, environmental variables determined spawning site selection. A piezometer is placed into the gravel using a slide hammer (left). Incubation baskets (center) are used to evaluate chum survival during intergravel development. Three baskets are buried around randomly selected piezometers (right). Click on image for larger view.

Initial hydraulic and water quality measurements were used to determine the appropriate sampling scheme for deployment of incubation basket groups. These in situ incubation baskets are used to evaluate the survival of eggs and alevins in relation to intergravel environmental conditions. During 1999, at both study sites, the eggs from three females were pooled and fertilized using three males. Eggs were counted into groups of 100 and each group placed into an incubation basket with sieved gravel. Incubation baskets were buried in clusters of three associated with individual piezometers. One basket from each group of three was removed at different life stages: one basket at the eyed-egg stage, one at the pre-emergent stage, and the third basket remaining in the gravel until emergence (Spring 2000). Egg baskets were examined, and individual eggs, alevins, and fry were enumerated and classified in the field as live or dead.

Results