From subsidy evaluation to effort estimation: Advancing the function of voyage data recorders for offshore trawl fishery management

Abstract

The overfishing of large vertebrates and shellfish is the first major disturbance to all the valuable coastal ecosystems that have been studied. However, usable logbook data has not been required or of concern in many small-scale fisheries operating in the coastal or offshore regions, rendering impact evaluation and further management difficult. Various studies have taken advantage of vessel monitoring systems (VMSs) that were originally developed for purposes such as surveillance, to derive high-resolution spatiotemporal effort data or further develop logbook-like data. These systems are usually installed on large-scale fishing vessels but seldom on small-scale vessels. Taiwan provides fuel subsidies to fishery operations, evaluated according to active moving hours at sea, as calculated with customized voyage data recorders (VDRs) that have been installed on most small-scale offshore fishing vessels. The device provides temporal position and speed data similar to that of VMSs, not in real time but with cheaper device cost, no data transmission fee and higher resolution at 3-min intervals. This paper takes the offshore trawl fishery of southwestern Taiwan as example to demonstrate that the VDR data used for subsidy evaluation could also be used for high-resolution effort estimation. After briefly documenting the development of Taiwanese trawl fisheries and the application of VDR in Taiwan, the paper proposes a simple five-step procedure for managers to categorize major fishing patterns of fisheries by reviewing the speed and track profiles of vessels on a trip-by-trip basis, and finally to develop speed criteria for defining fishing efforts.