Identifying populations of Pacific salmonids

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Identifying populations of Pacific salmonids

• Why important?
• Definition of a population
• Practicalities of identifying salmonid
  populations
• Upper Columbia River steelhead and spring-run
  chinook salmon
• Puget Sound chinook salmon
• Key research gaps

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Identifying populations of Pacific salmonids--why?

• Demographically independent units for
  conservation assessments
• Critical for evaluating viability at population
  and larger (e.g., ESU) scales
• Key for predicting responses of salmonids to
  management actions

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• An independent population is a group of fish of
  the same species that spawns in a particular lake
  or stream (or portion thereof) at a particular
  season and which, to a substantial degree, does
  not interbreed with fish from any other group
  spawning in a different place or in the same
  place at a different season.
• -Ricker (1972)

4

• An independent population is any collection of
  one or more local breeding units whose population
  dynamics and extinction risk over a 100-year time
  period are not substantially altered by exchanges
  of individuals with other populations.
• -NMFS Viable Salmonid Population draft document
  1999

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Evidence for independent populations

• reproductive isolation
• genetic similarity
• similarity in life history traits
• geographic distance between spawning groups
• dispersal among spawning groups
• habitat characteristics
• demographic data

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Spring-run chinook salmon in the Skagit River
Basin one population or more?

• Geographically disjunct spawning distributions
• Run/spawn timing distributions are similar
• Genetic distances suggest Suiattle, Cascade and
  Sauk fish are similar
• Abundance correlations are very low between
  Suiattle and Sauk

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Spring-run chinook salmon in the Skagit River
Basin one population or more?

• Geographically disjunct spawning distributions
• Run/spawn timing distributions are similar
• Genetic distances suggest Suiattle, Cascade and
  Sauk fish are similar
• Abundance correlations are very low between
  Suiattle and Sauk

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Quasi-extinction risk
0.961
0.551
0.803
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Consequences of lumping and splitting--Skagit
River spring chinook

• Quasi-extinction risk of streams alone
• upper Sauk 0.551
• Suiattle 0.961
• Quasi-extinction risk of streams combined
• upper Sauk Suiattle 0.803

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Key research gaps

• Methods for distinguishing effects of spatially
  correlated environments and dispersal between
  groups on correlations in abundance
• Integrating across indicators of population
  structure in a systematic way