Towed video footage and single beam sonar allowed for the detection and targeting of different benthic communities with the benthic sled, so species and functional groups could be identified and their distribution, abundance, biomass and size composition investigated.50 sites were sampled in 2006 and a further 12 sites were sampled in 2007. Sites were located at various depths in different habitats with varying degrees of benthos.
Due to the large size of some of the benthos collected (i.e. sponges and gorgonians) in the 2006 field work, the dimensions of the CSIRO designed benthic sled were sometimes inadequate for the purposes of our survey and a new sled was designed and built for the 2007 field work. The new steel benthic sled is based on the design of a commercial fishing Tri-gear Trawl Beam, slightly modified for our purposes. Traditionally a Tri-gear Trawl Beam is used to locate, track and sample scallops and deep water prawns in depths less than 1000 metres. The dimensions of the sled used at Ningaloo are 1.5 m wide x 1 m high. The net and cod end are made of 48 ply 2" Amican TM. It is a 4 seam net; top and bottom panels 100 meshes wide with wing panels 50 meshes high. It has a 9 bar 1 point taper with panels 75 meshes long with dimensions of 55 meshes long and 100 meshes round. The net and cod end are protected by rubber chafe matting designed to minimise damage from abrasive substrates (i.e. rock, coral). There is a double cod end to help secure the sample from being lost from a torn net.Trials indicated the new sled's sampling was an improvement on 2006 and all the macro benthos shown on towed video was being sampled. Trials also indicated that the most representative and manageable sled sample distance, out of several tested, was 50 metres in all the habitats sampled. Fifty metre long samples will be adopted as the standard for future samples to be carried out in 2008.
