Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 8775
Title: Observations of Steelhead in the California Current Lead to a Marine-Based Hypothesis for the Half-Pounder Life History, with Climate Change Implications for Anadromy
Author: Sean A. Hayes, Arnold Ammann, Jeffrey A. Harding, Jason L. Hassrick, Lynn deWitt, Cheryl A. Morgan
Publication Year: 2016
Journal: North Pacific Anadromous Fish Commission Bulletin
Volume: 6
Pages: 97-105
DOI: 10.23849/npafcb6/97.105
Abstract:

Steelhead typically spend little time in the California Current. Most emigrate each spring to the North Pacifi c for one or more years. During this migration, they track a narrow range of sea surface temperatures (SST). However, ship surveys off Oregon and northern California during 2007 and 2010–2014 observed steelhead in late June through August in the Klamath region where a microclimate corresponding to steelhead preferred SST persists through summer before warming in September. Cooler SST in the Klamath region may explain the presence of a life history, known as a “half-pounder”. Spring smolts remaining in this cool coastal region for the summer are eventually cut off from migratory pathways with preferred SST. We hypothesize that fi sh choose to retreat into local rivers to avoid a warming ocean in autumn. While the half-pounder life history is only common in a couple of regions, it has implications for all steelhead life histories at larger spatial scales. Specifi cally the 2014–2015 “warm blob” may have blocked thermal migratory corridors during winter and spring migrations for southern stocks. Expanded warming periods could lead to disruptions in the space-time continuum of these marine pathways with respect to acceptable SSTs, restricting access to ocean ecosystems for fi sh with anadromous life histories. An outstanding question for California steelhead is whether migration pathways will remain stable, or whether connectivity to North Pacifi c waters will change under potential climate change scenarios.

Full Text URL: http://www.npafc.org/new/publications/Bulletin/6/hayes_97-105.pdf