AEBR 372 The extent and intensity of seabed contact by trawl gear using fisherreported and geospatial position reporting data, 1990 to 2023

Using fisher-reported start and end points, and a method that assumes trawl paths follow straight lines between those points, the study analyses trends in different measures of seabed contact for these groupings. The measures include the area in square kilometres of the overall trawl footprints and aggregate (cumulative footprint) areas by year and all years combined, the number of tows, the number of cells contacted (a 5 km × 5 km grid overlaid on the fishable area), and the number of ‘new’ cells contacted each year that had previously not been contacted.

Key findings include:

• All Stocks (2008–2023): The area of seabed contacted each year declined over time, with the lowest footprint recorded in 2023. Each year, trawling activity affected between 1.7% and 2.3% of the total EEZ + TS seafloor, and between 5.0% and 6.8% of the fishable area (areas open to trawling down to 1600 m). The number of trawl tows dropped from nearly 89 000 in 2010 to about 55 000 in 2023.
• Deepwater Fisheries (1990–2023): The footprint expanded during the 1990s, reached its highest levels in the early 2000s, and then steadily declined to 2020, remaining relatively stable since. There was little expansion of effort into new cells in 2023 (8 cells and 4.3 km² footprint), with new cells probably representing the very edges of fished areas. 
• Inshore Fisheries (2008–2023): The footprint decreased from a peak in 2010 to its lowest in 2023, covering less than 1% of the EEZ +TS and about 2% of the fishable area in recent years. There was little expansion of effort into new cells in 2023 (14 cells and 3.6 km² footprint), with new cells probably representing the very edges of fished areas. 

Geospatial Position Reporting (GPR) data, introduced in 2018–19, allows for more accurate mapping of trawl paths by tracking vessel movements during fishing. This report also compares the straight-line method to a hybrid method, which combines GPR and fisher-reported data, to see how estimates differ for a selection of inshore and deepwater target species/species groups. It was found that the aggregate swept areas are almost universally higher for the hybrid approach but other measures can be more variable.

The project also explored whether GPR data could be used to create standard trawl paths to correct older records. While the approach shows promise, it is computationally demanding and unlikely to offer practical benefits for current fisheries management.

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