Total Allowable Commercial Catch
The Rock Lobster Fishery Management Plan requires annual stock assessment of the Victorian rock lobster resource to enable the review of the total allowable commercial catch (TACC). The Management Plan also requires that the fishery is assessed using prescribed stock performance indicators, biological reference points, triggers and a rebuild target that must be reached by 2020/21. The stocks in the Eastern and Western Zones are assessed separately.
The first step in the TACC setting process is to conduct an assessment of the rock lobster stocks using a stock assessment model. The results of the modelling are then tested against the rules in the management decision framework and a resultant TACC is established.
Stock Assessment Model
The stock assessment uses the 'rock lobster fishery stock assessment model', which has been designed for the assessment of rock lobster fisheries in Victoria, South Australia and Tasmania. The model is length-structured, analyses male and females separately, and tracks monthly the number of rock lobsters in the population that are equal to or larger than 60mm carapace length. It accounts for natural mortality, fishing mortality, and variation of animals in annual growth-increment, body mass and number of eggs produced by females.
The model estimates the two stock performance indicators that are prescribed in the Management Plan: 'egg production' and 'available biomass'. Egg production is a measure of the number of eggs produced by mature female rock lobsters in the population. Available biomass is a measure of the stock biomass of rock lobsters that can legally be caught.
The original decision framework described in the Management Plan was reviewed and simplified in 2011 (see Figure 1). The decision rules require the comparison of the stock performance indicators against the biological reference points of a limit and a target reference point.
- Limit reference point is equivalent to 20% of the estimated level of egg production in 1951.
- Target reference point is equivalent to 40% of the estimated available biomass in 1951.
Under the decision rules described in Figure 1, if a stock assessment indicates that egg production is below the limit reference point, a reduced TACC must be put in place to lift the egg production above the limit within two years. If the egg production is above the limit, the decision framework prescribes adoption of a TACC that reaches the target reference point for the available biomass by 2020/21.
The TACC is calculated using model-based forward projections which project the estimated available biomass from its current level to the 2020/21 target. The TACC for the next season can then be determined from this trajectory (see Figure 2 as an example).
The model estimated TACCs are then discussed in the Rock Lobster and Giant Crab Resource Assessment Group (RLRAG) before being approved by the Minister (or delegate).
The Victorian Rock Lobster Fishery Management Plan 2009 describes a comprehensive and multifaceted decision framework designed to set the total allowable commercial catch for the fishery. In 2011, in accordance with an action in the Management Plan to review of the decision framework, the framework was simplified into three clear steps (see below). The revised decision framework was put in place in 2012 (and replaces pages 16 and 17 of the Management Plan).
Figure 1: Revised Decision Framework – Victorian Rock Lobster Fishery Management Plan
Figure 2: Trajectory of available biomass required to rebuild the stock to the target by 2020/21