Why Do We Mark Fish?

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History

• Need to mark fish to get survival exploitation
  rates for Treaty negotiations, to determine
  differential survival of various release
  strategies to determine distribution in
  fisheries
• Started marking in BC with 1967 brood
• Use alpha-numeric tags, mainly on chinook and
  coho
• Use fin clips, mainly on other species except
  adipose clips on coho

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Types of Marking

• Coded-wire tags (CWT)
• Fin clips adipose (Ad), right or left ventral
  (RV/LV), right or left maxillary (RM/LM)
• Otoliths (has rings like a scale)
• Calcein- fluorescent dye in fins
• Passive-induced transponder (PIT) tags

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Tagging Pros Cons

• Lots of codes available- can identify different
  stocks or release strategies
• Can get survival and exploitation rates for
  individual stocks or release strategies
• Application is expensive
• Recovery may be expensive
• Fishery sampling is expensive
• Escapement sampling may not be very expensive if
  at fence or hatchery rack

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Finclipping Pros and Cons

• Can use as visual I.D.- for mass marking
• Application less expensive than CWT
• Few options for distinguishable codes
• Cant get survival exploitation rates
• Higher mortality from ventral/maxillary clips
  than from tagging
• Cant determine age class if use same clip every
  year - need scales too

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Otolith Pros and Cons

• Very inexpensive to apply
• No external visual I.D.
• Few options for distinguishable codes
• Sampling and reading of otoliths is expensive
• Cant determine age class if use same mark every
  year - need scales too

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Magnified Otolith
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Number to Tag/Mark

• For coho fry, need to tag at least 40K for
  distribution, 80K for survival exploitation
  rates (lower survival on fry release)
• Tag minimum 20K coho smolts or 75K chinook smolts
  for distribution in fisheries
• Tag 40K coho or 200K chinook smolts for survival
  exploitation
• For chum fry need minimum 100K finclips

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Costs of Marking

• Tags cost .09 per fish
• Contractor AdCWT application costs about .12 per
  fish
• Adipose clip costs about .05 per fish
• Tagging machines cost about 24,000 for the tag
  injector and 14,000 for the QCD (checks tag
  retention)

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CWT Recovery Data Availability

• Mark Recovery Program (MRP) reports- can get
  details down to exact sport catch locations and
  recoveries by week and statistical area for
  commercial fisheries
• SEP1 reports- Summary of fishery recoveries with
  escapement data added includes survival
  exploitation rates

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Tag Recovery Data Observed

• Observed is the number of a particular tag code
  actually found in a sample of fish in the catch
  or escapement
• observed in sport catch is turned in or
  found in creel survey
• Mark rate is the tagged in the total sampled

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Tag Recovery Data Estimated

• The estimated accounts for tags in the
  unsampled part of catch or escapement
• Calculated as observed / sample rate
• Sample rate is sampled of total catch or
  escapement (100 if all sampled)
• Aim for 20 sample rate in commercial fisheries
• Use sport awareness factor (creel survey)

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Tag Recovery Data Expanded

• The number expanded accounts for the unmarked
  fish released with a given tag group
• It is calculated from the number estimated /
  number released with tags total number released
  (in a given release group)

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Example of Estimation and Expansion of Observed
Tags

• Tag Code 18-28-11 (2000 brood Cowichan R
  chinook) 25,175 tagged of 99,829 total release
• Observed in 2003 escapement 3 tags in dead pitch
  sample of 527 and total river spawners 2,494
• Estimated 3/5272,494 14
• Expanded 14/25,17599,829 56

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Information from Tagging/Marking

• Identification of hatchery fish
• Distribution in fisheries
• Enhanced contribution
• Harvest or exploitation rate
• Survival rate

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Identification of Hatchery Fish

• For use in brood stock collection
• For use in hatchery mark-selective fisheries

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Distribution in Fisheries

• For interest- to see where a particular stock is
  caught
• Determine what fisheries to close or reduce to
  help preserve stocks of concern
• Determine what stocks are caught in mixed stock
  fisheries

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Chinook Distribution in Fisheries and Escapement,
2000-2005
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Coho Distribution in Fisheries and Escapement,
2000-2005
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Enhanced Contribution

• Determine whether the hatchery component in a
  river has exceeded some target (50)
• Determine how well the hatchery stock is
  performing (in conjunction with survival rate)

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Harvest/Exploitation Rate

• Harvest rate is the of fish surviving to
  adulthood caught in one fishery
• Exploitation rate is the overall of fish
  surviving to adulthood caught in all fisheries
• Determine harvest rates in individual fisheries
  for each stock
• Track harvest exploitation rates to make sure
  were not over-fishing

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Survival Rate

• Determine differential survival for different
  release strategies
• Determine differential survival for wild versus
  hatchery releases
• Track the trend in survival for warning of any
  problems developing

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Quinsam River Survivals
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Cowichan Chinook Survival
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