Comparative Use of Shallow and Deepwater Habitats by Juvenile Pacific Salmon in the Columbia River Estuary Prior to Ocean Entry

G Curtis Roegner,Laurie A Weitkamp,David J Teel

doi:10.1080/19425120.2016.1227889

Abstract

AbstractThe degree to which fine‐scale habitat use by salmonid species and stocks varies within habitat types such as estuaries is not fully resolved. We sampled shallow shoreline and deeper main‐stem channel habitats in the Columbia River estuary over 3 years to compare salmon species composition, migration timing, density, size, and production type (hatchery or natural). Results indicated a high degree of spatial heterogeneity in habitat occupancy by the five salmonid species that are native to the basin. Salmonid communities at two channel habitat sites were much more similar to each other than to the community at a shoreline site. Salmonids sampled at the shoreline site were primarily subyearling Chinook Salmon Oncorhynchus tshawytscha and Chum Salmon O. keta and yearling Coho Salmon O. kisutch, with few other salmonids present. In contrast, channel habitat contained a higher diversity of salmon species, with samples representing all species of anadromous salmonids, including Sockeye Salmon O. nerka and steelhead O. mykiss. Salmonids in deeper channel habitat were generally larger than salmonids found along the shore, and the proportion of hatchery‐origin salmon was also higher in deep channel habitats. On a per‐area basis, we also found much higher densities of salmon along the shoreline than in channel habitats. For Chinook Salmon, habitat use also differed by genetic stock of origin: upper‐river stocks primarily used deeper channels, while lower‐river populations used both channel and shoreline areas. We concluded that sampling at both habitat types is required to fully encompass the migration patterns of all salmon evolutionarily significant units in the Columbia River basin. These spatial and temporal variations in salmon timing and density have ramifications for feeding, growth, and competitive interactions. This study provides information that is relevant for conservation efforts targeting specific fish populations and efforts to evaluate the potential impacts of in‐water activities in the Columbia River estuary.Received May 12, 2016; accepted August 19, 2016

Highlights

Subject editor: Donald Noakes, Vancouver Island University, Nanaimo, British Columbia © G
Salmonids sampled at the shoreline site were primarily subyearling Chinook Salmon Oncorhynchus tshawytscha and Chum Salmon O. keta and yearling Coho Salmon O. kisutch, with few other salmonids present
Channel habitat contained a higher diversity of salmon species, with samples representing all species of anadromous salmonids, including Sockeye Salmon O. nerka and steelhead O. mykiss

Summary

Introduction

Subject editor: Donald Noakes, Vancouver Island University, Nanaimo, British Columbia © G. General patterns are thought to include the use of open-water migratory channels by active migrants, with shallow-water, shoreline, and wetland habitats being preferred by more estuarine-dependent fish (Dawley et al 1986; Bottom et al 2005) These distributions may reflect distinct life history characteristics based on genetic lineage, or they may represent the remnants of a wider continuum of evolutionary migration strategies that are limited by hatchery practices and habitat alterations. Subyearling Chinook Salmon arrive in the estuary over protracted migration periods depending on the stock of origin (Dawley et al 1986; Bottom et al 2005; Roegner et al 2012; Teel et al 2014; Weitkamp et al 2015). Hatcheries generally produce fish that are larger than naturally reared individuals and that are often smolted (Naish et al 2008; Tatara and Berejikian 2012)

Objectives

Methods

Results

Discussion

Conclusion