Adaptive management of a tropical mixed stock fishery

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Adaptive management of a tropical mixed stock
fishery
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Sainsbury 1988 . The ecological basis of
multispecies fisheries, and management of a
demersal fishery in tropical Australia. Pps
349-382 in Gulland, J.A. Fish Population
Dynamics 1988. John Wiley Sons Sainsbury
1991. ICES mar. Sci. Symp 193 301-320.
Sainsbury, K.J., Campbell, R.A., Lindholm, R.
and W. Whitelaw. 1997. Experimental management of
an Australian multispecies fishery Examining the
possibility of trawl-induced habitat
modification. pp. 107-112. In Pikitch, E.K.,
Huppert, D.D. and M.P. Sissenwine. eds. Global
Trends Fisheries Management. Bethesda American
Fisheries Society Symposium.
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The fisheries

• Japanese trawlers on lethrinids 1959-1963
• Taiwanese trawl 1972-1990 mixed species
  Nemipterus, Saurida, Lutjanus, Lethrinus
• Australian trap fishery 1984-- Lethrinus, Lutjanus

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Changes in catch rates
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Key points

• No decline in overall catch rate in trawl fishery
• Lutjanids, lethrinids and nemipterans are of
  equal value to trawl, saurids less valuable
• Trap fishery only has markets for lutjanids and
  lethrinids

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Alternative hypotheses

• H1 An intraspecific mechanism, under which the
  observed changes are regarded as independent
  single-species responses
• H2 An interspecific mechanism in which there is a
  negative influence of Lethrnius and lutjanus on
  the population growth rates of Saurida and
  Nemipterus so that Saurida and Nemipterus
  experience a competitive release as the abundance
  of Lethrninus and Lutjanus is reduced by fishing.
• H3 An interspecific mechanism in which there is
  a negative influence of Saurida and nemipterus on
  the growth rates of Lethrinus and Lutjanus, so
  that Lethrinus and Lutjanus are inhibited as the
  abundance of Saurida and Nemipterus increases for
  other reasons.
• H4 Habitat determination of the carrying capacity
  of each genus

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Annual net value in M AUS under three fishing
regimes
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Alternative actions

• WA continued Taiwanese Trawl
• WB immediately shift to long-term plan (U1)
• WC trawl for period t then switch
• WD close fishing for period t1 then switch to
  trap fishery for t2 years then switch to best U
• WE same as WD except spatial control

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Bounds on expected present value when policies
are either perfectly informative or
uninformative. WA is trawl, WB is trap F.1, WC
and WD use whatever U has highest estimated
expected value. No revenue from trawl closures
and 0.95 discount used
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Further options

• Within each plan, there is a question of which
  exploitation rate to allow.
• U1 trap F.1
• U2 trap F.2
• U3 trap F.6
• U4 continued trawl

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Present value of fixed actions
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Probabilities assigned after experimental periods
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