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Harvesting strategies and tactics

Harvest strategies. How regulations will change in relation to the state of the fisheryState will usually be estimated stock sizeMay also include price, other species, environment. Pacific halibut 35% vulnerable biomassPacific salmon fixed escapement targetsShould be robust to environmental changes.

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Harvesting strategies and tactics

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    1. Harvesting strategies and tactics Fish 458

    2. 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

    3. Harvest tactics The 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

    4. The three major classes of strategies Constant exploitation rate Constant escapement Constant catch

    5. Catch vs run size

    6. Mathematical form

    7. Typical projection - 2000 target

    8. Typical projection 50% h.r.

    9. Average Catch

    10. Average spawning stock

    11. Average catch vs average spawners

    12. Average catch vs cv of catch

    13. 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

    14. 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

    15. Size limits Commonly used in invertebrate fisheries and sport fisheries Set size above age at first reproduction

    16. 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!

    17. 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

    18. 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!

    19. 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

    20. Walters formula for sustainable harvesting Refugia economic - tropical tunas spatial - N. Cod before offshore trawling temporal - salmon size - lobsters

    21. Reference Points Guidelines for management May be exploitation rates or biomass based Two standbys are Fmax and Bmsy

    22. Fmax and F0.1

    23. Spawning biomass per recruit F35% F40% F45%

    24. 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

    25. 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

    26. 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

    27. Current Issues: stabilizing catch

    28. Current issues: management procedures

    29. 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

    30. 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?

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