Sea Technology

AUG 2012

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Deploying AUVs In Restricted Areas EcoMapper AUV Operates Under Environmental Constraints For Water Quality Monitoring of a Mussel Farm in Spain By David Roque Glider Technician Balearic Island Coastal Observing and Forecasting System Balearic Islands, Spain Pablo Rodríguez Technical Manager Autonomous Vehicle Laboratory Unidad de Tecnología Marina Consejo Superior de Investigaciones Cientificas Barcelona, Spain and Uxio Labarta Research Professor Department of Physiology and Mollusc Culture Instituto de Investigaciones Mariñas Consejo Superior de Investigaciones Cientificas Vigo, Spain M ussel culture is one of the most important economic ma- rine resources in Galicia, Spain, a region in the northwest of the Iberian Peninsula where mussel production is the highest in Europe. Most of these mussels grow in rafts that are grouped in farms. Conducting environmental studies of these sites is essential to determine the conditions for optimal growing rates in order to improve the aquaculture. Key variables in these studies are the amount of food, which is estimated from the fluores- cence of the water column, and the current velocity, an index of the water renewal time. In addition, the physico- chemical parameters, such as temperature, salinity, oxygen and turbidity, provide water quality information, which could help predict toxic algae blooms that could lead to farm closures and economic losses. Presently, the primary way to monitor these parameters in mussel farms is to employ sensors on moorings. How- ever, the use of AUVs can improve knowledge of the bio- geochemical processes occurring in these sites by obtaining data that complements information gathered from the mooring observatories. EcoMapper AUV in Galicia Mussel Farm YSI Inc.'s (Yellow Springs, Ohio) EcoMapper AUV, a small, portable vehicle, was used in an October 2011 study to collect bathymetry and water quality data in a mussel www.sea-technology.com AUGUST 2012 / st 21 farm in Lorbé, Galicia. The AUV has sensors for measuring CTD, dissolved oxygen, chlorophyll, pH, ORP (oxidation re- duction potential) and turbidity, as well as an acoustic Doppler current profiler (ADCP) and Doppler velocity log. A two-man team equipped with the EcoMapper visited the mussel farm to explore the possibility of collecting data by AUV. An AUV is greatly influenced by environmental conditions. The study was conducted under a worst-case scenario setup, providing an opportunity to test some of the EcoMapper's op- erational limits. There were several constraints on the vehicle's operations. Mussel farms are dynamic. Rafts are anchored at one point, but they move with the wind and tidal currents. The area of study was a very active mussel farm with several 30- ton service boats operating continuously, which presented the risk of collision with the AUV. The mussel farm was located on a small bay on the Rías Altas, with a beach surrounded by rocky cliffs. Options for an emergency path were limited, and no previous bathymetry or side scan data of the area existed. The seafloor below the mus- sel farm was full of debris, including anchors, ropes and mussel lines. In general, this region suffers adverse weather during au- tumn and winter. Survey Setup Preparation started with three steps that are general for all mini-AUV campaigns, while the fourth was specifically for Map of the study area at the Lorbé mussel farm, showing the final track of the AUV across the rafts.

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