Drivers of Toothfish Catchability

Project team
Ryan Downie, Ben Scoulding, Peter Oke, and Rich Hillary

Background
Patagonian toothfish (PTF) (Dissostichus eleginoides) subpopulations support high value Australian fisheries around the Heard Island and McDonald Islands (HIMI) and Macquarie Island (MI) regions. Recently, the HIMI PTF fishery has experienced a decline in catch rates that are not related to stock decline. One explanation is that changes to the species biophysical environment may be influencing availability or the catch efficiency of the fleet. In contrast, the MI PTF fishery has experienced an increase in catch rates. Due to their isolation, the long-term sustainability of these fisheries is dependent on interactions between large scale oceanography, ecosystem productivity and fishery management. Therefore, there is a need to determine the extent to which biophysical drivers influence catch rates.

Our approach
We will investigate how variation in environmental and ecological variables influence PTF catchability in both the HIMI and MI fisheries. This will be done by quantifying the relationships between fishery specific environmental, ecological, and economic variables using state-of-the-art spatiotemporal modelling techniques. The analysis will identify relationships between key variables under a variety of environmental conditions, that will be used to produce probabilistic maps of catchability to enhance the efficiency of this quota-managed fishery.

Aims
The aims of the project are to:

1. Develop a high-resolution oceanographic tool to map historical oceanographic data on the Kerguelen Plateau (KP) and Macquarie Ridge (MR)
2. Define PTF foraging habitats from historic bioacoustics data collected on-ground and by the IMOS BASOOP in the KP and MR
3. Investigate how historic bioacoustics data collected on-ground and by IMOS BASOOP can be used for seabed habitat classification on the KP and MR
4. Combine environmental, ecological, and economic covariates and catch histories to characterise variations in catchability.

Outcomes
We will provide the fishing industry and managers with an understanding of the relationships between environmental, ecological, and economic drivers of PFT catch rates in the HIMI and MI fisheries. If relationships can be established between oceanography, dynamic habitats and catch rates then a real time monitoring program could be developed to aid in catch efficiency.