Day 21: Mark Green, CSIRO
Scientists, fishery and marine natural resource managers need quantitative information on different species and their abundance at various locations. Traditionally, collecting this sort of information has involved catching fish. In the past few decades, as technology has become increasingly available and affordable, scientists have been developing non-extractive sampling methods. SCUBA divers can collect observations in shallower waters, but cameras can go a lot deeper.
One type of widely used moored camera system is the Baited Remote Underwater Video Systems, (BRUVS). The BRUVS either has a single, or more commonly a pair of cameras of video cameras, placed into waterproof housings and mounted in a weighted frame. A pole with a bag of berley bait attached is then placed in front of the camera, and the unit is dropped into water with a float line for recovery.
The simple BRUVS will record vision for about an hour before the storage is full and the battery is exhausted. These can then be pulled up, downloaded, new batteries and new bait fitted and redeployed to get several drops in over a day. This is suitable shallow water areas where the effect of current on the camera frame and float line are not of concern, and a small boat is economical to run close to shore. However, deep water presents a different set of challenges.
DeepBRUVS was designed and built by CSIRO for deep-water deployments. The frame is rugged and sturdy, and the camera housings are waterproof to 1000 metres. As sunlight does not reach beyond about 100 metres below the sea surface, lights are also attached. The DeepBRUVS has an extended recording capability of 20 hours and a huge battery, and the cameras and lights are programmable to turn on and off at specific times. They can be deployed and left for long periods on the seafloor. This means that using a long rope with floats for retrieval is no longer practical. Instead, DeepBRUVS have a mooring weight system, which can be acoustically released in response to a signal from the surface, allowing the system to float to the surface.
During this voyage, we are examining the effectiveness of various attractants to lure deep sea species to the BRUVS. The bag of berley will last about three days in the deep cold water (fridge temperatures of 3–4 °C), but will eventually lose its attractiveness through diffusion of the “smelly” bits, or it being eaten by the little crustaceans common on the seafloor. As part of the developmental process we are trying flashing coloured ‘carnival’ lights this time on one unit and comparing it to the unit with berley as the bait.
We have had three deployments now on the top of seamounts in depths of about 900 metres, and they have produced some interesting results. The vision from the baited unit shows eels and sharks swimming up to the berley bag, sometimes biting or just bumping it. The vision from the first deployment of the unit with flashing lights showed a lot of spikey oreos initially, which gradually moved away after the filming light came on. Unfortunately during the most recent deployment the intense pressure at depth was just too much for the ‘carnival’ light housing, and it imploded.
Our next DeepBRUVS deployment should happen soon and we will have one unit with the berley, and one with nothing. It has been suggested that just having the filming light will draw in fish. Nothing ventured, nothing gained!
I am really keen to try deployments using sound vibration as an attractant. Sound propagates very easily in water, and spreads in 360 degrees. This is unlike the ‘smell’ plume from the berley, which will only travel down current and will become diluted the further away from the bait bag. Unfortunately testing sound to attract deep sea fish will have to wait for another voyage. Maybe deep sea fish will like music, or the sound of waves breaking over rocks. Note to self, try rock music, maybe Pearl Jam!