Surveys of deepwater benthic communities using a benthic sled in Ningaloo Marine Park, Western Australia (WAMSI Node 3 Project 1 Subproject 3.1.1)

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.

拖曳式视频录像与单波束声呐可配合底栖拖网（benthic sled）对不同底栖生物群落开展探测与靶向采样，由此可实现物种与功能群的鉴定，并对其分布、丰度、生物量及体型组成进行调查。本数据集于2006年完成50个采样点的采样工作，2007年新增12个采样点的采样。所有采样点分布于不同栖息环境的多个水深梯度中，且各点位的底栖生物丰度存在差异。由于2006年野外采样中收集到部分体型较大的底栖生物（如海绵与柳珊瑚），由澳大利亚联邦科学与工业研究组织（CSIRO）设计的初代底栖拖网尺寸有时无法满足本次调查需求，因此团队为2007年野外工作重新设计并制作了新型拖网。这款钢制新型底栖拖网基于商用Tri-gear拖网梁（Tri-gear Trawl Beam）的设计理念，针对本次调查需求进行了小幅改造。传统Tri-gear拖网梁主要用于水深1000米以内海域的扇贝与深水对虾的定位、追踪及采样。本次在宁格罗（Ningaloo）海域使用的拖网尺寸为宽1.5米、高1米。拖网网身与囊网（cod end）均采用48层2英寸规格的Amican TM材料制成。该拖网为四缝式结构：上下网板宽度为100目，翼网高度为50目。拖网采用9杆1点的锥度设计，网板长度为75目，具体参数为长55目、围长100目。拖网网身与囊网均加装了橡胶耐磨垫，以最大限度降低粗糙底质（如岩石、珊瑚）对网具的损伤。此外，该拖网配备双层囊网，可有效防止因网具破损导致采样样本丢失。对比测试结果显示，新型拖网的采样效果优于2006年使用的初代设备，可完整采集拖曳视频中观测到的所有大型底栖生物（macro benthos）。同时，多组对比测试表明，在所有测试的采样距离参数中，50米为兼具代表性与可操作性的最优拖网采样距离。后续2008年开展的采样工作将统一采用50米长度作为标准采样距离。