Developing long-term monitoring programs in offshore waters with little prior knowledge: Comparison of GRTS based sampling with swath mapping

The Australian Commonwealth Marine Reserve (CMR) Network covers a total of 2.7 million square kilometres of continental shelf and slope, and abyssal habitat. Whilst many areas of continental slope habitats have been previously swath mapped, and benthic habitats characterised, relatively little is known about the habitats in the shelf and abyssal environments. The inability to extrapolate information to unsurveyed areas, represents a considerable challenge to the future management of biodiversity in the CMR estate, particularly for the shelf because it is where habitat diversity and many elements of biodiversity are expected to be relatively rich and where anthropogenic pressures are greatest. Here we report on the results of a pilot program undertaken in Flinders CMR (northeast Queensland), designed to test the costs and benefits of two approaches to characterising shelf habitats in the context of biodiversity management: (i) multibeam sonar mapping of a continuous (~30 km2) area judgementally selected on the basis of its representivity of seabed habitats, versus; (ii) targeted mapping of a greater number of smaller, but spatially balanced, locations using a Generalized Random Tessellation Stratified (GRTS) sample design. We present the first quantitative estimates of habitat type on the shelf of the Flinders CMR, using both approaches, and contrast the costs and quality of information that both approaches offer. We then consider the implications for future inventory of benthic habitats in shelf environments in the context of monitoring the CMR estate.