Develop and test a range of assessment models and methods to establish \(MSY\) or proxy reference points across the spectrum of data-limited stocks

• Choose Case Studies based on Economic value; Importance; Sensitivity to the impacts of fishing; Available data.

• A number of data-limited methods already exist, therefore implement a Common Framework to compare performance.

• Evaluate Sensitivity to assumptions

• Conduct Management Strategy Evaluation to ensure robustness to uncertainty

A Common Fisheries Programme objective is to achieve \(MSY\) for all harvested species

2020 deadline for achieving Good Environmental Status

• “Stocks should be exploited sustainably consistent with high long-term yields.”
• “Populations of all commercially exploited fish and shellfish are within safe biological limits,exhibiting a population age and size distribution that is indicative of a healthy stock.”

“2 over 3” catch rule to stabilise data limited stocks at current levels

Adjust catches based on changes in an index of abundance (\(I\))

Index goes up catch goes up, Index goes down catch goes down

Limitations

2 over 3 rule, however, has no reference points to ensure that

• Targets are met
• Limits are avoided with high probability

Opportunities

Under the CFP management plans should be delivered through a results-based approach that allows tailor-made measures to be proposed in close consultation with fishers and Member States at a regional level.

WKLIFE is testing rules that use \(MSY\) proxy reference points of the form

\(C_{y+1}=C_{current}rfb\)

Where

• \(r\) is a rule based on an index of abundance
• \(f\) is current exploitation rate relative to a \(F_{MSY}\) proxy
• \(b\) specifies a threshold which if the index falls below the catch is reduced.

“2 over 3”

“2 over 3” or Trend

Evaluate alternatives by constructing an Operating Model to simulate stocks with different life and exploitation histories

Generate different types of datasets using an Observation Error Model

Then test Alternative Management Procedures

• Assessment Methods
• Reference Points and
• Advice Rules

Turbot, Brill, Pollack, Ray, Sprat, Lobster, Razors

F and \(F_{MSY}\) Proxies

Based on Beverton and Holt \(L_{F} = \frac{L\infty +\frac{F+M}{K}L_c}{1+\frac{F+M}{K}}\)

• \(L_{current}/L_{F=M}\)
• \(M/(Z_{current}-M)\)
• \(F_{0.1}/(Z_{current}-M)\)
• \(LBSPR\) Length-based spawning potential ratio (Hordyk et al. 2015)
• \(Lime\) (Rudd and Thorson, 2018) mixed effects non-equilibrium
• …

Risks of an increase are different from a decrease, therefore

• K1 decreases catch if index declines

• K2 increases catch if index goes up

GES Descriptor 3 requires that stocks should be

• Exploited sustainably consistent with high long-term yields
• Have full reproductive capacity in order to maintain stock biomass
• Proportion of older and larger fish/shellfish should be maintained (or increased) being an indicator of a healthy stock

Safety

• Probability of avoiding limits >\(B_{lim}\)

Status

• Probability of achieving targets >\(B_{MSY}\) & >\(F_{MSY}\)

Yield

• \(Yield:MSY\)

Variability

• Inter-Annual

• K1 decreases catch if index goes down
• K2 increases catch if index goes up

• K1 decreases catch if index goes down
• K2 increases catch if index goes up

Case studies

• Summarise current knowledge and infomation
• Evaluate alternative management plans and data collection options

Evaluate Methods

• Length
• Abundance Indices
• Catch

Evaluate Combined Rules of the form \(C_{t+1}=C_{t-1}rfb\)

Compare to Category 1 rules

Management Procedures

Consider the data along with the assumptions, estimator and management and feedback between the various elements

Diagnostics

Compare across species, stocks, fisheries and advice rules

Value of infomation

Models are cheap, but data is expensive

Risk

An uncertainty that matters, what matters are management objectives

• FLR
  • FLife
  • mydas
  • mpb
• R Packages
  • LBSPR
  • MLZ
  • …