Catch Per Unit Effort (CPUE) from commercial logbooks is often used as an index of abundance in stock assessments. However, the use of commercial CPUE as an indicator of relative abundance can be problematic as the underlying assumption that commercial catch rates change linearly with abundance is often compromised. Although some factors that are reported in logbooks can be used to standardise CPUE, there are other sources of variation including:
• Modified fishing practices to target or avoid species to suit quota availability, meet market demands, or to comply with management arrangements.
• Differences in selectivity of fishing gear and use of bycatch-reduction devices.
• The combined impacts of multiple management restrictions on a fishery.
For example, gillnet operations in what was once the Northern Territory’s Shark Fishery now almost exclusively target Grey Mackerel. This change in practice has resulted in an index that is losing its relevance in assessing shark species.

Over 140 elasmobranchs are listed on CITES Appendix II, with the likely-hood that more species will be added in the future. Of the 11,082t of shark landed by the fishery since 2000, CITES listed Hammerheads comprise 17.25% of the shark catch. Other sharks caught by the fishery that were recently added to CITES Appendix II at the Nineteenth meeting of the Conference of the Parties Panama City (Panama), 14 – 25 November 2022 include: Grey Reef Shark, Dusky Whaler, Sandbar Shark, Lemon Shark, Whitecheek shark and all other members of the family Carcharhinidae (which include the Blacktip Shark complex that is the main shark species caught by the fishery - 4688t or 42% since 2000). These species will require a positive Non-Detriment Finding (NDF) and CITES export permit in order to be exported following the 12-month delay in implementation (i.e., December 2023). The fishery also catches Threatened, Endangered and Protected Elasmobranchs, some of which are also CITES listed.

Gillnet and longline effort has decreased since 2000 and there is significant latent effort in the fishery. There is a desire to utilise this latent effort, however, the CITES listing of the majority of sharks species caught in the fishery will increase scrutiny from State, Commonwealth and International environmental agencies, as well as NGOs. This heightened scrutiny will provide greater impetus to demonstrate that shark stocks are at sustainable levels and that fishing is being undertaken sustainably.

There is a strong need for independent survey methods to gain a better understanding of the abundance patterns of shark species over time that can contribute to the development of appropriate management of these species that meets environmental, fisheries, and conservation needs.

Surveying Northern Australia using longlining methods would provide a fishery independent estimate of relative abundance for sharks that would improve economic security and public confidence in sustainability. However, to make an informed decision of the feasibility of a survey a full understanding of the scope of work and cost required is needed. There is a need to look at existing long line surveys undertaken worldwide (e.g. in the USA and Bahamas), to understanding the methods undertaken and the time period required to develop accurate abundance estimates.

Australia’s fisheries span a large area of ocean. Australia has the world’s third largest Exclusive Economic Zone (EEZ), with an area of over 8 million km2. This zone contains mainly Commonwealth managed fisheries, with State jurisdictions mainly in coastal waters up to the 3 nautical mile limit. Australia's total wild-catch fisheries gross value of production is $1.6 billion, of which 28% is from Commonwealth fisheries and 72% from the smaller coastal inshore fisheries managed by state jurisdictions. The wildcatch fisheries sector employs about 10,000 people across Australia (https://www.awe.gov.au/abares/research-topics/fisheries/fisheries-and-aquaculture-statistics/employment).

The commercial fishing industry has a network of thousands of vessels working mainly in inshore waters around Australia. They can supply a potential platform for extensive and fine scale spatial and temporal monitoring of the waters of the continental shelf (0-1200m), from the surface to the ocean floor. Given that their livelihoods depend on it, they have a keen understanding of oceanographic conditions with respect to fish behaviour, feeding and spawning and the various oceanographic factors that may influence this. In some fisheries (e.g. surface tuna longlining), fishers eagerly seek and use readily available fine-scale oceanographic data such as sea surface temperature and sea level, to improve their targeting and achieve higher resultant catch rates. For many other fisheries, however, it is the fine-scale sub-surface oceanographic conditions (feed layers, thermoclines, temperature at depth etc) that have a critical influence on their fishing dynamics. Unfortunately, this type of oceanographic data is far less readily available. Although fishers and scientists know these factors are important, the time series of fine scale spatial and temporal data relevant to fishery operations is not available to include in stock assessments. As a result, it is often assumed that variations in catch rates reflect changing stock abundance, when it may simply be a result of changing oceanographic conditions.

Marine scientists collect a vast range of oceanographic data using satellites, subsurface drones, and static and drifting buoys. Sea surface data, however, is much easier and more cost-effective to collect at high spatial and temporal resolutions than sub-surface data. Hence, understanding of sub-surface oceanographic conditions tends to be derived from modelling more than actual measurement. This may be sufficient at a wide-scale global or continental level, but it is not adequate at the fine-scale spatial and temporal resolution required for fisheries management.

The use of commercial fishing gear as a research data platform has been increasing in popularity internationally (https://www.frontiersin.org/articles/10.3389/fmars.2020.485512/full). A number of groups in Europe have been doing this for a decade (e.g Martinelli et al 2016), and New Zealand are also now involved (https://www.moanaproject.org/te-tiro-moana). However, this approach has yet to be implemented in Australia in a coordinated way. In particular, our approach dictates open access data served through the IMOS Australian Ocean Data Network (www.aodn.org.au) that can be collected once and used many times.

In this project we intend to instrument seafood sector assets (e.g Trawl Nets, longlines, pots) with fit-for- purpose quality-controlled (QC'd) temperature/pressure sensors to increase the sub-surface temperature data coverage around Australia’s shelf and upper slope regions (0-800m) at low cost. Not only will this assist in the collection of data at relevant spatial and temporal scales for use by fishers, but it will also provide a far more extensive level of QC’d data to oceanographers in near real time (NRT) for evaluation and ingestion into data-assimilating coastal models that will provide improved analysis and forecasts of oceanic conditions. In turn, this will also be of value to the fishing sector when used to standardise stock assessments.

Martinelli, M., Guicciardi, S., Penna, P., Belardinelli, A., Croci, C., Domenichetti, F., et al. (2016). Evaluation of the oceanographic measurement accuracy of different commercial sensors to be used on fishing gears. Ocean Eng. 111, 22–33. doi: 10.1016/J.OCEANENG.2015.10.037