How are the Status of Australian Fish Stock Reports done

How are the Status of Australian Fish Stock Reports done?

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Over 100 leading Australian fisheries researchers have worked to deliver the Status of Australian Fish Stock Reports.

These Reports rely on a consistent national reporting framework that was developed collaboratively by fisheries scientists from around Australia. This is a major step forward for Australian Fisheries and provides transparency and consistency across the jurisdictions.

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.

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. To classify stocks into one of these categories, the current abundance and level of fishing pressure are compared with defined biological reference points. 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 2018 refers specifically to the biological status of fish stocks, and does not take into account broader ecological or economic considerations.

The term 'stock status', as used in the Status of key Australian fish stocks reports 2018, 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.

The tables below show the classification system used in the Reports.

To understand these tables, it is important to keep in mind the following points:

  • A fish stock in influenced by two parameters: recruitment and mortality.
    • Recruitment is the number of fish that enter the stock, that is the fish that are old enough/big enough to be caught. In order to ensure constant recruitment, there has to be enough fish of breeding age (spawning biomass) left in the water, so that the population can replenish itself.
    • Mortality can be due to natural causes or fishing but in this context we are considering the fish that die due to fishing.
  • If the fishing pressure (mortality due to fishing) is too high, the fish won’t have time to reproduce enough before they are caught and over time the stock will become depleted. This is because there are not enough young fish entering the stock to replace the ones that have been fished.
  • As measuring the number of fish in the water can be very difficult, proxies are often used to estimate stock levels.
  • Biomass is the weight of all the fish considered.

Image overview of Stock Status Classification System 2018

 

Here the same information in a little more detail

  Stock status Description Potential implications for management of the stock
  Sustainable Biomass (or proxy) is at a level sufficient to ensure that, on average, future levels of recruitment are adequate (recruitment is not impaired) and for which fishing mortality (or proxy) is adequately controlled to avoid the stock becoming recruitment impaired (overfishing is not occurring). Appropriate management is in place.
  Depleting Biomass (or proxy) is not yet depleted and recruitment is not yet impaired, but fishing mortality (or proxy) is too high (overfishing is occurring) and moving the stock in the direction of becoming recruitment impaired. Management is needed to reduce fishing mortality and ensure that the biomass does not become depleted.
  Recovering Biomass (or proxy) is depleted and recruitment is impaired, but management measures are in place to promote stock recovery, and recovery is occurring. Appropriate management is in place, and there is evidence that the biomass is recovering.
  Depleted Biomass (or proxy) has been reduced through catch and/or non-fishing effects, such that recruitment is impaired. 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.
  Undefined Not enough information exists to determine stock status. Data required to assess stock status are needed.
  Negligible 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.

The Reports were coordinated and managed by the Australian Government’s Fisheries Research and Development Corporation (FRDC).

Preparing the Status of Australian fish stocks Reports is a large undertaking with many jurisdictional agencies contributing both funds and researchers to complete the national assessments. Key agencies involved in developing this edition are listed in the Acknowledgements page.

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Reference points

Biological reference points provide guidance on determining whether stock abundance is too low or fishing pressure is too high.

As required under the UN Fish Stocks Implementation Agreement and FAO Code of Conduct, Reference points in a fishery generally include targets to indicate where we would like to be, and limits to show what to avoid.

Stock assessments usually produce estimates of abundance and fishing pressure over time, which can be assessed against biological reference points.

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Limit reference points

A limit reference point is a level of fish abundance which requires management intervention.These points have historically varied across Australian jurisdictions.

For assessing fish stock status nationally, 'recruitment impaired' was agreed as the biological limit reference point for determining whether or not a fish stock is depleted.

The percentage of the unfished abundance that represents a recruitment impaired classification varies across species and stocks, based on differences in biology. The recruitment impaired limit reference point for abundance in the Status of Australian fish stocks reports is different from the limit reference points defined in some jurisdictions, which may include economic considerations or a precautionary buffer against measurement uncertainty.

For a stock to be classified as sustainable in SAFS, the current level of fishing pressure must be such that it is unlikely the stock will become recruitment impaired.

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Target reference points

Target reference points correspond to levels of biomass and fishing pressure that are considered to provide for optimal harvests, taking into account economic considerations and/or broader ecological requirements for each fish stock.

Generally, fisheries management aims to ensure that stocks are maintained near target levels and away from limit levels.

Target reference points commonly incorporate management objectives, such as maximising the sustainable yield or economic returns. For example, the Commonwealth Fisheries Harvest Strategy Policy seeks to maintain fish stocks, on average, at a target biomass equal to the biomass that would produce maximum economic yield. As with limit reference points, a range of target reference points is currently used in the different fisheries and jurisdictions across Australia.

There is no single agreed national target level and these may vary substantially between stocks, so it is challenging to include status classifications based on targets in stock status determinations. Although the stock status determinations provided in these reports report against limit reference points, it is envisaged that, in the future, stock status classification may consider stock status in relation to targets as well as limits.

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Fish stocks

The Status of Australian fish stocks reports 2018 focuses on the status of biological fish stocks wherever possible. It is important to distinguish between biological stocks and fisheries. Biological stocks are relatively discrete populations of a fish species, usually in a given geographical area and with limited interbreeding with other biological stocks of the same species. Biological stocks are natural resources, and different biological stocks may have different natural abundance, growth rates and mortality rates. Different biological stocks may also be influenced by different environmental factors, depending on where they occur. As a result, the amount of catch that can be sustainably removed may vary from one biological stock to another, even within a species.

Although one fish species may exist in many geographical locations around Australia (or worldwide), fish caught in different areas may come from separate biological stocks. Individual biological stocks may be found in a single jurisdiction or may be shared across two or more jurisdictions. In some cases, individual biological stocks may also extend into the high seas. The size and distribution of individual biological stocks vary greatly between species. For example, Southern Bluefin Tuna comprises a single biological stock that spans much of the world's southern oceans. In comparison, hundreds of separate biological stocks of Blacklip Abalone are thought to exist in Australia. Because separate biological stocks have limited connectivity, fishing one would affect that stock, but may not directly affect others. It is therefore important to assess each biological stock separately, where possible.

In contrast, fisheries are management units engaged in harvesting fish. Fisheries are typically defined in terms of the people involved, the species caught, the area of water or seabed fished, fishing methods and the types of boats used. A single biological stock may be caught by one or a number of fisheries. Similarly, a single fishery may catch one or a number of different species, from one or more different biological stocks. Some of the species and biological stocks fished by Australian fisheries are migratory, and are taken in both the Australian EEZ and the high seas or the EEZ of other countries.

A key measure of fisheries management performance is the status of the fish stocks—the natural resource on which the fisheries depend. Therefore, the Status of Australian fish stocks reports 2018 provides status classification for fish stocks. Where possible, this takes into account the impacts of all fisheries at the level of individual biological stocks. Where the stock delineation is not known (that is, it is not known exactly where one biological stock finishes and the next begins) or the numbers of biological stocks for a species are very high, reporting has been undertaken at the level of either the jurisdiction or the management unit. The level of reporting (biological stock, management unit or jurisdiction) for each species is presented at the beginning of each chapter, along with the rationale for this choice. In these reports, the term 'stock' is used generically to refer to all three levels of stock status assessment—biological stocks, management units and populations assessed at the jurisdictional level. In future, it is hoped that most species currently assessed at the management unit or jurisdictional level will be assessed at the biological stock level, wherever research has been able to determine the biological boundaries of the stocks for the species.