Habitat Use by Juvenile Chinook Salmon in the Nearshore Areas of Lake Washington: Effects of Depth, Lakeshore Development, Substrate, and Vegetation

Abstract

Juvenile Chinook salmon Oncorhynchus tshawytscha in nearshore areas of Lake Washington, Washington, were studied to determine their depth distribution, substrate associations, and use of overhanging vegetation (OHV) and shoreline armoring. From March to May, juvenile Chinook salmon progressively shifted to deeper waters as they increased in size. At night, they were associated with small substrates, whereas no association with a particular substrate type was detected during daytime. Juveniles were commonly found in open areas or within 5 m of overwater structures (e.g., piers and docks) but were rarely found directly under such structures. The number of juveniles associated with armored shorelines was lower than expected given the availability of this habitat type. Large numbers of small juveniles often used OHV during the day; however, at night they moved away from cover and occupied open areas with no structure. Larger juveniles did not show a strong affinity to overhead cover. Our results suggest that continued development of the Lake Washington shoreline has the potential to restrict the amount of habitat that is useable by the Chinook salmon. They used shallow shoreline areas with fine substrates (sands and gravels), including both open beaches and areas with riparian vegetation for providing woody debris and OHV. These types of habitat features tend to be reduced as a result of lakeshore development. We hypothesize that habitat use by juvenile Chinook salmon was most likely being driven by predation risk. Habitat changes resulting from shoreline development could therefore potentially increase their vulnerability to predators.

Received November 30, 2010; accepted June 1, 2011

ACKNOWLEDGMENTS

Sean Rubey, Chuck McCoy, Sergio Camacho, David Low, and Heather Tschaekofske (USFWS) assisted with field sampling. Personnel of the City of Renton, Washington, provided logistic support for field sampling. Steve Dilley and Scott Sanders (USFWS) assisted with the figures. Kelly Kiyohara (Washington Department of Fish and Wildlife) provided information on Chinook salmon emigration. The study was financially supported by Seattle Public Utilities and administered by Keith Kurko and Julie Hall. Comments provided by Julie Hall (Seattle Public Utilities), Michele Koehler (Seattle Public Utilities), Ken Tiffan, Jim Johnson, and an anonymous reviewer greatly improved earlier versions of the manuscript. The findings and conclusions in this article are those of the authors and do not necessarily represent the views of USFWS.