Complete Manuscript Describing Marine Habitat Use
by Chinook Salmon Off the Coasts
of California and Oregon During Autumn

Current Status of Accomplishment or Milestone: Manuscript submitted to Marine Ecology Progress Series on January 16, 2004, initial revisions completed and submitted on May 10, 2004 final revisions completed and submitted on August 9, 2004 final version accepted for publication on August 12, 2004.

Background: Describing the ocean habitats used by Chinook salmon Oncorhynchus tshawytscha is an important step toward understanding how environmental conditions influence their population dynamics.  This manuscript is the first manuscript to be published from the data collected as part of the PFEL’s ongoing habitat research.

Purpose of Activity/Goal of Project: Identify and describe Essential Fish Habitat for Chinook in the marine environment and develop an understanding of how these fish respond to changing ocean conditions at both individual and population scales.

Description of Accomplishment and Significant Results: We used data from archival tags that recorded time, temperature and pressure (depth) to define the coastal habitats used by Chinook near Oregon and California during the autumns of 2000, 2002 and 2003. We used a clustering algorithm to summarize the data set from each year and identified four general habitats that described the set of ocean conditions used by Chinook.  The four habitats, defined primarily by depth and the time of day that these depths were occupied, were characterized as 1) shallow day, 2) shallow night, 3) deep, and 4) deepest.  The definitions and use of each habitat were similar across years and the thermal characteristics of all habitats included water temperatures between 9-12ºC.  This temperature range provided the best indicator of Chinook habitat in the coastal ocean.  Chinook used 9-12ºC water at least 52% time.  Less than 10% of surface waters within the area where Chinook were released and recovered provided these temperatures.  Cross sections of subsurface temperatures suggest that between 25% and 37% of the coastal water column was available to Chinook and contained water in the 9-12ºC range.  These results support hypotheses that link salmon-population dynamics to ocean temperatures.  Continued monitoring of surface and subsurface thermal habitats may be useful for assessing the extent and quality of conditions most likely to sustain Chinook populations.

Significance of Accomplishment (e.g., to the Center, to Management, and to NMFS Strategic plan Goals): This manuscript identifies the conditions that Chinook actually experience while at sea off California and Oregon.  Identifying these conditions will improve the ability of the NMFS to describe how changing ocean conditions may influence the production of these stocks.

Problems: None.

Key Contact: George Watters (831-648-0623, George.Watters@noaa.gov)