Tracking fishermen : using GIS to characterise spatial distribution of fishing effort in the Tasmanian abalone fishery

Major collapses of abalone fisheries around the world have been preceded by a spatial serial depletion of abalone populations. As in other fisheries, this serial depletion has been difficult to anticipate and to understand without fine scale monitoring and analysis of spatial effort distribution. In recent years a field of fisheries science has started to evolve which looks at the spatial distribution of fishing effort in commercial fisheries and spatial fleet dynamics, and novel applications of some GIS tools are being developed. Despite the relative health of the Tasmanian abalone fishery (a $A100 million fishery) compared to other abalone fisheries around the world, many aspects of the reporting and assessment process require improvement to ensure sustainability of the fishery. History has shown that reliance on catch and temporal effort data reported at large spatial scales (current Tasmanian practice) is inadequate for assessment of abalone stocks, or for detecting spatial depletion. Traditional fishery independent methods used to estimate population abundance (both relative and absolute) are also inadequate, and prohibitively expensive for monitoring fishery stability. In this study, GPS data loggers were deployed on abalone fishing boats and set to record latitude and longitude of boat position every ten seconds. Divers wore depth loggers to record information about when divers were actively fishing. A novel aspect of this study is the combination of GPS fishing data and GIS tools, generally applied in animal behaviour analyses, to quantify the spatial distribution of fishing effort as captured by the loggers. The ability of these methods to describe complexity of diver behaviour, concentration of diver effort and contraction of the fishery were assessed. The use of GPS loggers provided high spatial resolution data on fishing activity, and improved the quality of fishing effort data available. Describing spatial distribution of fishing effort at fine scales captures information about changes in that spatial distribution. Performance measures of Catch Per Unit of Area fished were developed and demonstrated in the context of fishery assessment. Kernel density estimates of fishing activity during single fishing events are proposed as measures of fishing behaviour. Adoption of simple behavioural indices (dive duration as an indicator of fishing success) was proposed to enhance traditional Catch Per Unit Effort based stock-assessment methods. Subject to field validation, the performance measures developed in this study can be used to forewarn fishers and advise managers of depleting fish stocks.