Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 4532
Title: Ichthyoplankton distribution and abundance in relation to nearshore dissolved oxygen levels and other environmental variables within the Northern California Current System
Author: Angela Johnson, L. Ciannelli, Richard D. Brodeur
Publication Year: 2015
Journal: Fisheries Oceanography
Volume: 24
Issue: 6
Pages: 495-507
Keywords: Ichthyoplankton,hypoxia,vertical distribution,environmental effects,California Current,

Nearshore hypoxia along the coast of Oregon and Washington is a seasonal phenomenon that has generated concern among scientists studying this temperate upwelling ecosystem.  These waters are affected by coastal upwelling-induced hypoxia mainly during late summer and fall, but effects of low oxygen levels on fish and invertebrate communities, particularly during early-life history stages recruiting and settling during the summer and fall, are poorly known.  We investigated the effects of hypoxia on the species composition, density, vertical, and horizontal distribution of fish larvae along the Oregon and Washington coasts during the summers of 2008, 2009, and 2010.  Bottom dissolved oxygen (DO) values ranged from 0.49–4.79 mL L-1 over all sample years, but the overall water column DO values were only moderately hypoxic during the three years of sampling compared to previous extreme years (e.g., 2002 and 2006).  DO was not a dominant environmental parameter driving the species composition of this study.  Instead salinity and Julian Day had the strongest correlations with species composition.  Although the overall density of fish larvae with increasing bottom-DO values, the effect on individual species density was limited.  Slender sole (Lyopsetta exilis) and sand sole (Psettichthys melanostictus) were the only species to have significant relationships with DO and both showed negative relationships.  Finally, in some locations fish larvae altered their vertical distribution when bottom-DO was low by ascending into shallower water layers.  Our results indicate that larval fish spatial distribution was not greatly affected within the range of observed values, but more continuous sampling, over a greater range of DO values, is necessary to better characterize the effect of hypoxia on the ichthyoplankton community of the Oregon and Washington coast. 

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Theme: Ecosystem Approach to Management for the California Current Large Marine Ecosystem
Foci: Describe the interaction between human activities and ecosystem status and resilience.
Characterize linkages between climatic conditions and biotic responses.