Stock status classification system

Stock status classification system

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In general, stock status classifications assess whether the current abundance (number or biomass [weight]) of fish in a stock is at an adequate level and whether the level of fishing pressure (the amount of fish being removed through fishing) is adequately controlled through management. The terminology, criteria and reference points used for stock status classification can vary between species and jurisdictional status reports.

The abundance of a wild fish stock is usually compared with the abundance of that same stock before any fishing had taken place. Abundance is considered to be adequate if there is a large enough proportion of the original adult stock remaining that production of juveniles (recruitment) is not significantly reduced. That is, the abundance of adults has not been reduced to the point where there is increased risk of recruitment failure. This level of adult abundance will vary between different species of fish.

In terms of fishing pressure, stock status considers whether the current level of fishing pressure is adequately controlled to ensure that the stock abundance is not reduced to a point where production of juveniles is significantly reduced. Where information is available, level of fishing pressure includes consideration of Indigenous and recreational (including charter) fishing as well as commercial fishing.

The classification system agreed on by the Status of Australian fish stocks reports Advisory Group combines information on both the current stock size and the level of catch into a single classification for each stock (Table 1; Figure 4). To classify stocks into one of these categories, the current abundance and level of fishing pressure are compared with defined biological reference points (see 'Reference points', below). Each stock is then classified as a sustainable stock, transitional–recovering stock, transitional–depleting stock, overfished stock or environmentally limited stock.

The environmentally limited classification was introduced to the 2014 edition of the Status of Australian fish stocks reports. Stocks are classified as environmentally limited if the spawning stock biomass has been reduced to the point where average recruitment levels are significantly reduced, primarily as a result of substantial environmental changes/impacts or disease outbreaks (that is, the stock is not recruitment overfished). Fisheries management must have also responded appropriately to the environmental change in productivity.

For ease of interpretation, the classifications are depicted by a traffic light colour-coding system. An 'overfished stock' classification (red) indicates that a management response is required, to ensure the sustainability of the stock in question.

The term 'sustainable stock' in the Status of Australian fish stocks reports 2016 refers specifically to the biological status of fish stocks, and does not take into account broader ecological or economic considerations. A sustainable stock classification is given to stocks that are above the biological limit reference point of 'recruitment overfished' (see below) and for which the level of current fishing mortality is considered unlikely to cause the stock to become recruitment overfished.

The term 'stock status', as used in the Status of key Australian fish stocks reports 2016, does not have the broader meaning of terms such as 'ecologically sustainable' or 'ecologically viable', which consider the sustainability of the entire ecosystem and the role of specific stocks in the function of the ecosystem (see glossary for full definitions). It is envisaged that broader ecological considerations will be considered in future in companion reports.

Table 1: Stock status terminology for the Status of Australian fish stocks reports 2016

 

Stock status

Description

Potential implications for management of the stock

 

Sustainable

Stock for which biomass (or biomass proxy) is at a level sufficient to ensure that, on average, future levels of recruitment are adequate (i.e. not recruitment overfished) and for which fishing pressure is adequately controlled to avoid the stock becoming recruitment overfished

Appropriate management is in place

Transitional–recovering

Recovering stock—biomass is recruitment overfished, but management measures are in place to promote stock recovery, and recovery is occurring

Appropriate management is in place, and the stock biomass is recovering

Transitional–depleting

Deteriorating stock—biomass is not yet recruitment overfished, but fishing pressure is too high and moving the stock in the direction of becoming recruitment overfished

Management is needed to reduce fishing pressure and ensure that the biomass does not deplete to an overfished state


Overfished

Spawning stock biomass has been reduced through catch, so that average recruitment levels are significantly reduced (i.e. recruitment overfished). Current management is not adequate to recover the stock, or adequate management measures have been put in place but have not yet resulted in measurable improvements

Management is needed to recover this stock; if adequate management measures are already in place, more time may be required for them to take effect

 

Environmentally limited

Spawning stock biomass has been reduced to the point where average recruitment levels are significantly reduced, primarily as a result of substantial environmental changes/impacts, or disease outbreaks (i.e. the stock is not recruitment overfished). Fisheries management has responded appropriately to the environmental change in productivity

Appropriate management is in place

 

Undefined

Not enough information exists to determine stock status

Data required to assess stock status are needed

   Negligible Stocks do not form part of a cross jurisdictional biological stock, catches are so low as to be considered negligible and inadequate information exists to determine stock status Assessment will not be conducted unless catches and information increase
                                                                                                                               
Figure 4: Diagrammatic representation of stock status classification system, with relative spawning biomass (the ratio of current spawning biomass to the recruitment overfished spawning biomass limit) on the x axis and relative fishing mortality (the ratio of current fishing mortality to the fishing mortality that would cause the stock to become recruitment overfished) on the y axis.

Figure 4: Diagrammatic representation of stock status classification system 

* Note that part of the transitional–recovering block has been marked as 'overfished'. This represents stocks for which adequate management measures have been put in place, but these have not yet resulted in measurable improvements. Since environmentally limited stocks are not below the limit reference point as a result of fishing pressure, they are not included in this diagram.