Spatial assessment using geo-referenced diver data: a case study from North-West Tasmania

Australian Abalone Fisheries typically target spatially structured stocks, often in remote areas. The nature of these fishing operations means precise recording of fishery-dependent data is challenging, and fishery independent data collection to determine stock status is cost prohibitive. Typically, we see that assessments of these fisheries are based on large reporting blocks, with imprecise data. Information on spatial structure and stock productivity, and dynamics of the fleet are typically lost. Dynamic international exchange rates, increasing aquaculture production, and rising fuel prices have created a changed economic climate, with a corresponding modification in harvest strategies employed by divers, or imposed by quota owners. This requires different and more precise methods of assessing fishery performance than was required previously.

Capturing the changes in fisher behaviour and fleet dynamic are central to attribution of changes in CPUE signals to stock decline or, changed harvest strategy, or both. An electronic data collection and analysis system has been developed at the University of Tasmania, using GPS and depth/time data loggers to collect high-resolution, high-quality spatial location and effort data from abalone divers. Between 2008 and 2010, use of GPS and depth data loggers was mandatory for fishing in small section of coast in North-west Tasmania. Performance measures utilising the geo-referenced diver data and hotspot analyses are utilised to assess the capacity of fine-scale electronic spatial data to detect serial depletion.