About this document
This is a prototype of an automatic report that documents how the user specified the operating model and their various justifications.
Introduction
This MERA file follows closely the document
The primary reference for this MERA case study is the 2015 stock assessment: Ziegler, P., and Welsford, D. 2015. An integrated stock assessment for the Heard Island and the McDonald Islands Patagonian toothfish (Dissostichus eleginoides) fishery in Division 58.5.2. WG-FSA-15/42. https://www.ccamlr.org/en/wg-fsa-15/52
Referred to as the ‘assessment report’ or ‘assessment’ herein
Fishery Characteristics
Longevity
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Answered
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Very short-lived (5 < maximum age < 7)
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Short-lived (7 < maximum age < 10)
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Moderate life span (10 < maximum age < 20)
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Moderately long-lived (20 < maximum age < 40)
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Long-lived (40 < maximum age < 80)
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Very long-lived (80 < maximum age < 160)
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Justification
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The ‘moderately long lived’ option is a reasonably close match to the range stated in the assessment document 0.155 (Table 7, page 14)
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Stock depletion
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Answered
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Crashed (D < 0.05)
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Very depleted (0.05 < D < 0.1)
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Depleted (0.1 < D < 0.15)
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Moderately depleted (0.15 < D < 0.3)
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Healthy (0.3 < D < 0.5)
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Underexploited (0.5 < D)
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Justification
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The stock assessment estimates current spawning stock levels between 50% and 75% of unfished (Figure 14, page 26).
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Resilence
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Answered
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Not resilient (steepness < 0.3)
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Low resilience (0.3 < steepness < 0.5)
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Moderate resilence (0.5 < steepness < 0.7)
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Resilient (0.7 < steepness < 0.9)
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Very Resilient (0.9 < steepness)
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Justification
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Steepness was assumed to be 0.75 (Table 7, page 14)
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Historical effort pattern
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Answered
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Stable
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Two-phase
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Boom-bust
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Gradual increases
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Stable, recent increases
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Stable, recent declines
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Justification
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Fishing mortality rate is not explicitly provided in the assessment report but is estimated (catch over vulnerable biomass) to be increasing rapidly in recent years.
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Inter-annual variability in historical effort
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Answered
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Not variable (less than 20% inter-annual change (IAC))
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Variable (maximum IAC between 20% to 50%)
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Highly variable (maximum IAC between 50% and 100%)
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Justification
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There appears to be very little variability in fishing mortality rate around the underlying trend.
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Historical fishing efficiency changes
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Answered
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Declining by 2-3% pa (halves every 25-35 years)
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Declining by 1-2% pa (halves every 35-70 years)
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Stable -1% to 1% pa (may halve/double every 70 years)
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Increasing by 1-2% pa (doubles every 35-70 years)
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Increasing by 2-3% pa (doubles every 25-35 years)
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Justification
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Since effort in the previous question was mimicking fishing mortality trends historically, stable catchability is assumed.
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Future fishing efficiency changes
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Answered
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Declining by 2-3% pa (halves every 25-35 years)
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Declining by 1-2% pa (halves every 35-70 years)
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Stable -1% to 1% pa (may halve/double every 70 years)
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Increasing by 1-2% pa (doubles every 35-70 years)
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Increasing by 2-3% pa (doubles every 25-35 years)
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Justification
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Future fishing efficiency is assumed to be stable.
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Length at maturity
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Answered
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Very small (0.4 < LM < 0.5)
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Small (0.5 < LM < 0.6)
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Moderate (0.6 < LM < 0.7)
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Moderate to large (0.7 < LM < 0.8)
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Large (0.8 < LM < 0.9)
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Justification
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The assessment maturity ogive implies 50% maturity at around half of asymptotic length.
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Selectivity of small fish
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Answered
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Very small (0.1 < S < 0.2)
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Small (0.2 < S < 0.4)
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Half asymptotic length (0.4 < S < 0.6)
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Large (0.6 < S < 0.8)
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Very large (0.8 < S < 0.9)
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Justification
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Currently fishing selectivity first captures fish around 1/4 of asymptotic length.
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Selectivity of large fish
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Answered
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Asymptotic selectivity (SL = 1)
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Declining selectivity with length (0.75 < SL < 1)
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Dome-shaped selectivity (0.25 < SL < 0.75)
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Strong dome-shaped selectivity (SL < 0.25)
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Justification
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Selectivity is assumed to be dome-shaped with decreasing selectivity of larger individuals
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Discard rate
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Answered
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Low (DR < 1%)
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Low - moderate (1% < DR < 10%)
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Moderate (10% < DR < 30%)
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Moderate - high (30% < DR < 50%)
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High (50% < DR < 70%)
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Justification
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Discarding is assumed to be very low.
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Post-release mortality rate
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Answered
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Low (PRM < 5%)
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Low - moderate (5% < PRM < 25%)
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Moderate (25% < PRM < 50%)
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Moderate - high (50% < PRM < 75%)
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High (75% < PRM < 95%)
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Almost all die (95% < PRM < 100%)
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Justification
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Inconsequential given the previous question, however discarding rate is thought to be high for most gears.
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Recruitment variability
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Answered
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Very low (less than 20% inter-annual changes (IAC))
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Low (max IAC of between 20% and 60%)
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Moderate (max IAC of between 60% and 120%)
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High (max IAC of between 120% and 180%)
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Very high (max IAC greater than 180%)
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Justification
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Year class strength rarely varied more than 60% according to the assessment (Figure 10, page 23)
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Size of an existing MPA
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Answered
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None
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Small (A < 5%)
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Small-moderate (5% < A < 10%)
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Moderate (10% < A < 20%)
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Large (20% < A < 30%)
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Very large (30% < A < 40%)
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Huge (40% < A < 50%)
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Justification
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No closures currently.
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Spatial mixing (movement) in/out of existing MPA
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Answered
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Very low (P < 1%)
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Low (1% < P < 5%)
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Moderate (5% < P < 10%)
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High (10% < P < 20%)
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Fully mixed
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Justification
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Inconsequential given previous question.
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Size of a future potential MPA
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Answered
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None
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Small (A < 5%)
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Small-moderate (5% < A < 10%)
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Moderate (10% < A < 20%)
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Large (20% < A < 30%)
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Very large (30% < A < 40%)
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Huge (40% < A < 50%)
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Justification
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A hypothetical 10-20% future MPA is considered.
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Spatial mixing (movement) in/out of future potential MPA
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Answered
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Very low (P < 1%)
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Low (1% < P < 5%)
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Moderate (5% < P < 10%)
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High (10% < P < 20%)
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Fully mixed
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Justification
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Mixing is assume to be unknown.
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Initial stock depletion
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Answered
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Very low (0.1 < D1 < 0.15)
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Low (0.15 < D1 < 0.3)
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Moderate (0.3 < D < 0.5)
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High (0.5 < D1)
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Asymptotic unfished levels (D1 = 1)
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Justification
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The assessment assumes the stock is ‘unfished’ in the first historical year.
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Management Characteristics
Types of fishery management that are possible
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Answered
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TAC (Total Allowable Catch): a catch limit
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TAE (Total Allowable Effort): an effort limit
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Size limit
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Time-area closures (a marine reserve)
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Justification
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1. Describe what, if any, current management measures are used to constrain catch/effort.
TAC control is the current approach.
2. Describe historical management measures, if any.
Coming soon!
3. Describe main strengths and weaknesses of current monitoring and enforcement capacity.
Coming soon!
4. Describe and reference any legal/policy requirements for management, monitoring and enforcement.
Coming soon!
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TAC offset: consistent overages/underages
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Answered
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Large underages (40% - 70% of recommended)
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Underages (70% - 90% of recommended)
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Slight underages (90% - 100% of recommended)
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Taken exactly (95% - 105% of recommended)
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Slight overages (100% - 110% of recommended)
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Overages (110% - 150% of recommended)
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Large overages (150% - 200% of recommended)
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Justification
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I assume that enforcement is relatively good and TACs are taken exactly.
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TAC implementation variability
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Answered
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Constant (V < 1%)
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Not variable (1% < V < 5%)
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Low variability (5% < V < 10%)
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Variable (10% < V < 20%)
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Highly variable (20% < V < 40%)
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Justification
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I assume that enforcement is relatively good and TACs are taken exactly.
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