Halibut, Climate, and Fisheries Oceanography

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Halibut, Climate, and Fisheries Oceanography

• Steven R. Hare

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Background and motivation

• In January 1997, the IPHC began a 3 year
  Fisheries Oceanography project
• Commission has a long history of interest in
  environmental impacts on halibut
• Observed trends in halibut size and recruitment
  not entirely explainable by stock size
• Changes appear to parallel trends noted in other
  marine populations of the North Pacific
• Goal to better understand factors affecting
  growth and recruitment

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Bering Sea ecosystem changes in 1997-98

• Record warm SSTs in spring 1997
• Strongly stratified and shallow mixed layer,
  nutrient depletion, coccolithophore blooms
• Record biomass levels of jellyfish
• Massive seabird die-offs in 1997
• Disastrous salmon runs in 1997 and 1998
• Cetacean densities jump and new populations seen

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1998 Bering Sea coccolithophore bloom
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Interdecadal changes in halibut recruitment
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Total recruitment
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Long-term mean
Eastern GOA
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British Columbia
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Western GOA
Millions of 8 year olds
Southeast Alaska
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6
4
2
0
1930
1940
1950
1960
1970
1980
1990
2000
Year class
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Interdecadal changes in halibut size-at-age
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1997-98 project activities

• Definition of North Pacific decadal-scale climate
  variability and regime shifts
• Developed conceptual bottom up model of
  population variability
• Examined patterns of recruitment variability for
  North Pacific pelagic, groundfish and salmon
  species
• Compilation of a North Pacific ocean bottom
  properties database
• Analysis of recent growth changes

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Pacific climate variability, 1900-1997
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Physical and biological changes associated with
the PDO

• Warmer air and sea temperatures
• Decreased precipitation
• decreased upper ocean mixed layer depth
• More frequent and violent storms in the North
  Pacific

• Radical reorganization of lower trophic level
  species mix in GOA
• Plankton, salmon (Alaska), flatfish populations
  increased
• Crustaceans, marine birds, marine mammals, salmon
  (West Coast) declined

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Conceptual Model of ClimaticallyDriven Ecosystem
Change
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Patterns of recruitment variability
Salmon catches
Groundfish and pelagic recruitment
SPECIES SIGNAL EFFECT EBS A. flounder PDO
EBS G. turbot PDO - GOA A.
flounder PDO GOA P. halibut PDO
WC P. hake ENSO GOA pollock ENSO
GOA P. cod ENSO
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Ocean Bottom Properties Database

• Database for use in environmental studies
• Compilation of 145,000 records of near-bottom
  observations on temperature, salinity, dissolved
  oxygen and nutrients
• Geographic coverage Bering Sea to California,
  continental shelf and slope to 1000 m
• Sources include agency, university, foreign
  collections
• Funding being sought to digitize other
  collections
• Frequent requests for data

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Ocean Bottom Temperature data, by decade
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Decadal variation in bottom temperatures
change from 1971-76 to 1977-82
change from 1986-90 to 1991-95
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Summary of change in weight-at-age
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Changes in halibut size-at-age in the commercial
fishery
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Changes in halibut size-at-age in the commercial
fishery
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Gulf of Alaska groundfish and halibut
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Current and ongoing research

• Continue research on nature of climate
  variability
• Continue retrospective analyses using the ocean
  properties database
• Analyze historical variations in otolith growth
• Collaboration on basin-wide zooplankton biomass
  variability study
• Compare growth studies across groundfish species
• Construct environmentally based recruitment index
  
• IPHC is co-sponsoring two international symposia
  on interdecadal variability in groundfish stocks