Harvesting strategies and tactics

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Harvesting strategies and tactics

• Fish 458

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Harvest strategies

• How regulations will change in relation to the
  state of the fishery
• State will usually be estimated stock size
• May also include price, other species, environment

• Pacific halibut 35 vulnerable biomass
• Pacific salmon fixed escapement targets
• Should be robust to environmental changes

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Harvest tacticsThe regulations used to achieve
the strategy

• Time closures
• Area closures
• Gear restrictions
• Vessel or size restrictions

• Pot limits
• Size limits
• Bag limits
• Trip limits
• Total Quota

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The three major classes of strategies

• Constant exploitation rate
• Constant escapement
• Constant catch

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Catch vs run size
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Mathematical form
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Typical projection - 2000 target
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Typical projection 50 h.r.
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Average Catch
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Average spawning stock
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Average catch vs average spawners
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Average catch vs cv of catch
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Periodic harvesting

• Also known as pulse harvesting
• geoducks, clear cut logging
• good if large economies of scale
• good if old individuals are particularly valuable
  and there is no possibility of size/age selective
  harvesting

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Sex specific harvesting

• Take the males, they are pretty useless
• Used primarily in fisheries where animals can be
  returned to the water with good chance of
  survival and sex can be determined
• Crabs, lobsters etc
• Caution - Alaska crabs crashed despite males only
• How to calculate needed sex ratio

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Size limits

• Commonly used in invertebrate fisheries and sport
  fisheries
• Set size above age at first reproduction

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Walters dilemma

• We dont estimate abundance very well, even for
  trees 20 error is good
• Fish are like trees except they are invisible and
  they move
• estimates of abundance can easily be off by 100
• Recent halibut abundance revised upwards 300
• With a 35 harvest rate, if our estimate was
  double, we would set the quota at a 70 of stock
  size
• This is what happened with northern cod!

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Walters solution

• Dont use TACs
• Close enough of the space and time fishing
  opportunities that there is a realistic maximum
  harvest rate
• This has worked for Pacific salmon

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Why Walters is a crack-pot

• Such closures would mean an end to the many major
  fisheries - just what Walters wants to avoid!
• Many fisheries rely on fishing the population
  when it is at its most aggregated and thus
  totally vulnerable
• But he has a very good point!

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Alternative solutions to Walters Dilemma

• Be much more cautious - stay on the right hand
  side of the yield curve
• Be much more pro-active and be prepared for rapid
  changes in quota
• Accept much higher risk than we normally admit

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Walters formula for sustainable harvesting

• Refugia
• economic - tropical tunas
• spatial - N. Cod before offshore trawling
• temporal - salmon
• size - lobsters

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Reference Points

• Guidelines for management
• May be exploitation rates or biomass based
• Two standbys are Fmax and Bmsy

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Fmax and F0.1
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Spawning biomass per recruitF35 F40 F45
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20 virgin biomass rule

• RICC Francis
• Accept no policy that has allows the stock to
  drop below 20 of virgin biomass no more than 10
  of the time
• Problems - arbitrary, may be too cautious for
  some species, not cautious enough for others

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What is generally agreed

• It is better to be at biomasses larger than BMSY
• For reasons of risk, economics and ecosystems
• That spatial management should be commonly
  employed

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Current controversies

• If we believe we are lower than BMSY, how
  important is it to increase biomass, and at what
  cost
• increase in yield may be little if any
• economic costs can be great - SNA1
• ecosystem benefits are unclear and depend greatly
  on objectives

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Current Issues stabilizing catch
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Current issues management procedures
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Current controversies

• Establishment of no-take zones
• push for 20-30 default no-take
• clear protection benefits
• does one pattern of closures work for all species
• An alternative is explicit spatial management on
  a fishery by fishery basis

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Current controversies

• Is ecosystem management possible in harvest
  regulation
• What is meant - including people, trophic
  interaction, environmental forcing?
• Can we estimate parameters and use models, or
  just adopt broad sweeping guidelines?
• How do we value species of no commercial value?