Distribution and Productive Capacity of Coho Salmon in the Nome and Unalakleet River Drainages of Norton Sound.

Introduction: This project will use a habitat-based approach to estimate the escapement of coho salmon needed to seed the rearing habitat in selected Norton Sound tributaries, for the eventual purpose of estimating ranges of biological escapement goals (BEGs). Coho salmon distribution and smolt abundance will be described to quantify useable rearing habitat and to determine the smolt production of a Norton Sound stream. These data will be the essential building blocks for estimates of coho smolt production within the watershed and for estimates of the number of coho spawners needed to achieve this production. The distribution and production estimates will entail the collection of other key coho salmon life history data such as seasonal habitat use, age structure, and size, will include the collection and description of other salmon species, and will thereby address other information gaps identified by the Norton Sound Research and Restoration Plan (NSRRP).

Coho salmon represent an unusual opportunity to examine habitat-based biological escapement goals because of the coho's extended freshwater rearing time and the relatively straightforward correlation between production and basic habitat measures. Numerous authors have investigated relationships between fish abundance in streams (adult spawners, smolt yield, fry density, etc.) and physical habitat variables such as water temperature, flow, depth, velocity, water quality, food availability, channel characteristics (e.g. Bradford et al. 1997, Holtby et al. 1990, Marshall and Britton 1990, Pess et al. 2002, Reeves et al. 1989, Nickelson et al. 1992, Rosenfeld 2000, Jowett 1992). These multivariate models require intensive amounts of data for specific habitat characteristics and may or not be suitable beyond specific species, streams or geographic regions. More usefully for Norton Sound coho salmon, Bradford et al. (1997) examined mean smolt abundance and physical habitat features in 86 western North American streams and found that only stream length, and to a lesser extent latitude, was useful in predicting mean smolt abundance. Mean coho salmon smolt abundance was strongly correlated with stream length (R2 = 0.70, p<0.001; Bradford et al. 1997).

Statement of Work: The production of coho smolts throughout two Norton Sound drainages will be estimated from field studies of juvenile coho distribution and smolt production conducted in the summer and fall of 2003. The seasonal distribution of juvenile coho salmon in the Nome and North rivers will be estimated to determine the freshwater bottleneck and available habitat for pre-smolts.

The first task in 2003 will document seasonal coho juvenile distributions in the Nome and North rivers. Each stream will be surveyed with minnow traps in late spring, mid-summer, and late fall to capture coho salmon. Captured coho will be batch-marked with one of eight location / color combinations of elastomer jaw tags (Olsen and Vollestad 2001) to document movement over the course of the season. The results will indicate how much the distribution changes with season and will provide a comparison of actual ranges with those estimated in the initial production estimates generated in 2002.

For the second program, a weir will be installed on a Nome River tributary and emigrating coho smolts will be counted for the duration of the run to estimate total smolt production. Size, weight, and age data will be collected for analysis of condition and age structure. This site will then be evaluated for its potential as a "keystream" site that can be used to collect annual data on coho smolt biology, smolt production, and exploitation rates.

The results from these two sampling programs will be used to estimate the total amount of coho juvenile habitat in the two drainages and the smolt production from this habitat. Using estimates of sex ratio, fecundity and survival, the number of spawners needed to achieve the range of estimated smolt production will then be calculated.

Results/Work to Date: This project had a modest start, but was highly modified through large expansions at the request of the STC, the technical advisors to the Norton Sound Steering Committee. Initial work done in 2002 was the classification of the waters on the Nome and North Rivers by characteristics of stream order and gradient. Estimates of available rearing habitat were made, and minimum and maximum estimates of coho smolt production were made based on relationships discovered in coho streams in Southeast Alaska and British Columbia.