Abundance estimates are used both directly and indirectly in stock assessment processes to support fishery management. Australia’s fisheries research agencies all estimate fish population abundance in some way. These include genetic and conventional tagging, acoustics (active and passive), trawl and egg surveys, as well as using proxies of abundance such as catch. Each of these methods have benefits, biases and caveats linked to the method and to the fish species being assessed. For example, differences between life history and habitat can make an abundance estimation method that has worked for one species unsuitable for another. As the application of each method of estimating abundance is potentially species/scenario specific, potential use by researchers and managers can be fraught.

In developing or proposing an abundance estimate for use in fisheries assessment, researchers must have a clear understanding of the assessment framework in order to make sure that an abundance estimate can be used. Claims such as “this time series can then be used in stock assessment” must be verified by funding agencies (particularly beyond FRDC) and defensible. Proliferation of abundance estimation methods without links to the assessment process will not yield an expected benefit beyond knowledge accumulation.

A project is needed to capture the range of methods of estimating abundance for management purposes, and specify the conditions of use, limitations and readiness level for operational use. A decision tree and methods ‘toolbox’ that describes the techniques, their relative strengths and weaknesses will help researchers and managers identify the best suited abundance estimate approach, and guide research effort to overcome known weaknesses.

The development of a ‘toolbox’ of techniques would be used to inform:
1. techniques available to estimate abundance
2. suitability of them to different conditions such as life history, and data availability
3. requirements of the technique such as methods used, prerequisite expertise, data and cost; and
4. circumstances under which the technique can be used.
This project would also identify potential new approaches and technologies that might complement or replace current ones.

The marine waters of Southeast (SE) Australia are one of a series of global ocean-warming hotspots. In this region, the East Australian Current is extending pole-wards, resulting in warming of ocean surface at a rate four times the global average. Many species have extended their distributions southward, with potential changes in local abundance. In addition, climatic extreme events, such as marine heatwaves, are leading to additional impacts in the region. Projections show that these changes, and the associated biological responses, are expected to continue in the next century.

In this hotspot lie important fisheries, providing the bulk of fresh fish to Melbourne and Sydney markets. The Southern and Eastern Scalefish and Shark Fishery (SESSF) has a total catch of about 20,000t and a value above $80 million. Concerns about the ecological, economic and social sustainability of this fishery raised in the public, and by scientists, over the years, have prompted a series of management responses, initiatives and regulations. In the hotspot also lies an Australian Marine Reserve network established to protect and maintain marine biodiversity and ensure the long-term ecological viability of Australia's marine ecosystems.

Observations from the Australian commercial fisheries regulator, the Australian Fisheries Management Authority (AFMA) suggests that the abundance of some species have declined, while others have increased. Additionally, some species that have been historically over-fished do not seem to be recovering despite reduced fishing pressure. The South East Australian Marine Ecosystem Survey will seek to answer the questions:

1. Despite reduced fishing pressure, have fish abundances in the SESSF really declined in 25 years? And if so, why?

2. Are species shifting their ranges to places outside of where they have been historically found, including to the continental slope?

3. What are the prospects for the future?

Comprehensive bio-physical and ecosystem assessments of the shelf were last conducted 25 years ago. This project will repeat the surveys to document changes, and will establish a new baseline for the continental slope. Specifically, it will help answer the broad questions:

1. How and why have fish assemblages and species abundances changed in the southeast ecosystem, and can the causes be mitigated?

2. How does this affect the multiple-use management of the region for fisheries, conservation and biodiversity and the hive of activity from oil & gas, and renewable energy sectors?