Can vessel monitoring system data also be used to study trawling intensity and population depletion? The example of Australia's northern prawn fishery

TLDR

The study investigates whether VMS data from Australia’s northern prawn fishery can be used to assess trawl tracks, trawling intensity, and resulting stock depletion. The authors simulated VMS data by subsampling GPS fixes at various polling intervals and analyzed high‑frequency VMS records across fishing grids to evaluate track accuracy and effort patterns. Simulations showed that VMS with polling intervals longer than 30 min cannot accurately estimate trawl tracks, while high‑frequency VMS data revealed concentrated, non‑random trawling (up to 28 passes in some grids) with variable impacts across years, and catch‑depletion analysis indicated that catch‑per‑unit‑effort and cumulative catch may not reflect target‑species biomass, underscoring significant benthic impacts in productive areas.

Abstract

We explore the potential of using data from Australia's northern prawn fishery (NPF) vessel monitoring system(s) (VMS) to examine trawl track, trawling intensity, and stock depletion due to trawling. We simulate VMS data by subsampling global positioning system (GPS) fixes from the NPF fishing vessels at different polling intervals to examine their accuracy in describing trawl tracks. The results of the simulations suggest that VMS data with polling intervals longer than 30 min cannot accurately estimate trawl tracks. The analysis of high-polling-frequency VMS data collected in four (later reduced to three) 6 nautical mile × 6 nautical mile grids that historically received high levels of fishing effort showed that trawling was not random and some areas were trawled up to 28 times in the tiger prawn fishing season and the impact varied among years. The results of a catch-depletion analysis suggest that fishery catch-per-unit-effort and cumulative catch may not be proportional to overall target-species biomass in areas with highly aggregated trawl effort. The VMS data also showed a large number of trawls can occur in productive areas and that trawling impacts on benthos may be quite marked.