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Recruitment Processes Program

A Collaborative Effort to Improve Assessment of the Early Life History Stages of Important Commercial Fish Species in the Bering Sea

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Apr-May-June 2012
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The Fisheries Oceanography Coordinated Investigations (FOCI), the Ecosystem Monitoring and Assessment (EMA) and the Midwater Assessment and Conservation Engineering (MACE) Programs have begun a comprehensive, collaborative effort to improve assessment of the early life history stages of important commercial fish species in the Bering Sea. The effort will provide seasonal fisheries information, environmental and biological indices, and annual syntheses necessary to apply an ecosystem approach to management.  Specifically, the coordinated research focuses on studying processes during the first year of life, a time when climate variation has a large affect on survival.

This spring, the first two in a series of collaborative seasonal cruises were completed.  Scientists departed Kodiak, Alaska, aboard the NOAA ship Oscar Dyson for the Bering Sea on 26 April 2012 (cruise DY-12-04).  Along the way they deployed long-term oceanographic moorings in Chiniak and Pavlov Bays and accomplished ichthyoplankton and CTD (conductivity-temperature-depth) sampling in Shelikof Strait (Gulf of Alaska).  However, sea ice in the eastern Bering Sea covered the mooring sites and precluded retrieval of FOCI’s sentinel moorings there.  Scientists quickly adapted and began an ichthyoplankton survey over the southwest Bering Sea shelf, which was originally scheduled for the second cruise (DY-12-05). 

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Figure 1.  Preliminary densities (also known as rough counts) of walleye pollock larvae and locations of mooring deployments and recoveries from two FOCI cruises April 26 – June 2, 2012.  Note that many walleye pollock eggs were collected along the Alaska Peninsula in the early part of the cruise, however eggs were not rough counted at sea.  The timing of sampling may explain, in part, the difference in larval abundance between the southern and more northern areas.

 
   
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Figure 2.  Bill Floering (PMEL), Dave Hermanson and Brian Kibler (NOAA Marine Operations) deploy a surface mooring aboard the Oscar Dyson at Bering Sea mooring site M2. Photo by Kathy Hough (Marine Operations).

   




The objectives of this survey were to assess the distribution and abundance of eggs and larvae of walleye pollock (Theragra chalcogramma), examine the interactions among climate, oceanography, and ichthyoplankton, and determine how physical and biological factors affect the transport and survival of fish larvae.  At the end of the first cruise, the moorings were still covered with ice (see "The Bering Sea:  Current Status and Recent Events" in PICES Press v. 20 no. 2, in press for an explanation).  The survey was resumed at the beginning of the second cruise (DY-12-05) which began on 15 May.  Scientists were able to survey two known spawning grounds of walleye pollock over the shelf, the Unimak Island vicinity of the Alaska Peninsula and the Pribilof Islands.  They also were able to begin surveying presumed spawning areas north of Pribilof Canyon but ran out of time and were unable to complete the survey as far as Zhemchug Canyon.  This coverage was over a much larger geographic area than scientists were previously able to search.  Most of the ice-free portions of the survey area were successfully sampled for ichthyoplankton (Fig. 1) and other zooplankton, along with temperature and salinity profiles at each bongo station.  Data on distribution and abundance of zooplankton will provide information on prey fields for developing larvae.  Throughout the cruise, walleye pollock larvae were collected to assess condition and study bioenergetics, work which will be conducted in the laboratory by AFSC scientists Ron Heintz and by Steve Porter.  This work is central to understanding climate-mediated variation in condition of young walleye pollock in the spring and summer of the first year of life.  Scientists were also able to complete mooring recoveries and redeployments for the two southern Bering Sea mooring sites (M2 and M4, Fig. 2).  This will continue the long-term physical observations collected by the Pacific Marine Environmental Laboratory side of the FOCI program.  These measurements are critical to studying climate change and oceanographic variability.

Stay tuned for the next article examining this first year of life study when the three programs collect late summer/early fall data on the Oscar Dyson (August – October) to see how the fish have been growing since last spring and whether or not they have managed to store enough energy to survive their first winter. 

By Daniel Cooper and Janet Duffy-Anderson

 


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