Transcript Developing tools for EBFM in Australia

Review of the harvest strategy for the
Commonwealth small pelagic fishery
Tony Smith
Hobart, March 24, 2015
CSIRO WEALTH FROM OCEANS FLAGSHIP
Outline
• What is a harvest strategy?
• The current SPF harvest strategy
• The review
• Results
• Conclusions
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What is a harvest strategy?
A harvest strategy is the set of rules used to make decisions about
catch or effort levels in a fishery
• typically decisions are made every year, e.g. deciding on the
annual total allowable catch (TAC)
• the input to a harvest strategy is information on the current or
recent status of the stock
• a decision rule is used to translate stock status into a management
decision (catch level)
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The current SPF harvest strategy
• Input into the strategy is the latest egg survey estimate of stock
size for each stock
• There are three “tier” levels for the harvest strategy depending on
how recent the information is on stock size
• Tier 1: survey in last 5 years
• Tier 2: survey older than five years
• Tier 3: no recent survey
• The TAC is set using a harvest rate (HR) applied to the most recent
survey estimate – a proportion of that estimate
• e.g. Tier 2: the HR is 7.5%, so if the most recent stock size estimate
is 10,000t, the TAC would be750t
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The current SPF harvest strategy
For the current harvest strategy
• The Tier 1 HR averages 15% (steps 20, 17.5, 15, 12.5, 10 each year
as the survey ages)
• The Tier 2 HR is 7.5% (half Tier 1), with a maximum possible value
of 5,000 t
• The Tier 3 TAC is set at 500 tonnes
• The Tier 1 and 2 harvest rates are the same for all species and
stocks
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The review
• The current SPF harvest strategy was adopted in 2009
• It is normal practice to review these every five years or so
• This review was funded by FRDC and CSIRO
• Two objectives:
1. Provide advice on best practice reference points for the four
main target species
2. Provide advice on suitable harvest rates to achieve management
objectives for the four main target species in the SPF*
* Note: east and west stocks considered separately
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Methods – objective 1 – Atlantis SPF
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Methods - objective 1
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Results – objective 1
• Simulated different depletion levels for each stock and for all
stocks together
• Looked at how other species and trophic groups in the model
changed in abundance due to effects of fishing the SPF species
• Basic finding – minimal impact on predators and other species in
the ecosystem
• Why?
• No species rely entirely on SPF species
• Most predators are opportunistic feeders (eat what is available)
• From previous work – get bigger impacts of fishing krill or
mesopelagics (lantern fish, myctophids)
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Predicting tuna diets
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Methods – objective 2
• Test different harvest strategies to see which ones best meet
management objectives (achieve targets and avoid limits)
• The targets (biomass relative to unfished biomass) have been
informed by results from objective 1 – aiming for 50% depletion
• The limits are specified in the Commonwealth Harvest Strategy
Policy – less than 10% chance of falling below 20% of unfished
biomass
• Test various scenarios for applying Tier 1 and Tier 2
• Test for robustness to uncertainty in frequency and accuracy of
surveys, stock productivity, fishery selectivity
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Results – objective 2
• Looked at harvest rates that would result in a 50% chance of being
above or below B50 (half the unfished biomass)
• HR at Tier 1 to achieve the target and avoid the limit varies across
the species:
•
•
•
•
Blue mackerel – 23%
Jack mackerel – 12%
Redbait – 10%
Sardine – 33%
• Taking account of uncertainties (probability of exceeding the
limits) could lower the values for blue mackerel and sardines slightly
• Tier 2 HR – still half that for Tier 1 – can improve performance by
having more frequent surveys
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Conclusions
• No evidence found that harvest rates should be lowered to
account for trophic impacts
• This is for the longer term and at the population level and does not
consider shorter term effects such as localised depletion
• Results for the harvest strategy suggest modifications to the
existing Tier 1 rates, involving reductions for redbait and Jack
mackerel and increases for sardine and blue mackerel
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Thank you
Oceans and Atmosphere
Research Flagship
Tony Smith
WEALTH FROM OCEANS