Cefas and Liquid Robotics have recently deployed, tested and recovered a remotely-piloted Wave Glider, which was adapted to allow scientists to collect broadband fisheries acoustics data.
As part of a multi-vehicle mission under the UK NERC/Defra funded AlterEco project, the Wave Glider called Lyra was deployed in the central North Sea about 270 km north-east of Newcastle-upon-Tyne, UK by RV Cefas Endeavour.
The glider spent 41 days at sea, repeatedly covering a 64 km long transect along which valuable data were collected under different conditions, before finally being recovered 20km off Lowestoft.
While deployed, the Wave Glider was remotely piloted 24/7 by the Liquid Robotics’ operations team from their California headquarters in Silicon Valley almost 9000 km away and covered over 1700 km at sea.
For this mission, Cefas’ Lyra was fitted with the new Simrad EK80 broadband echosounder with two transducers (200kHz and 70kHz), utilizing a version of the electronics that has been specifically designed for autonomous surface vehicles called the WBT Mini. The system was self-contained with its own dedicated battery and used in standalone mode.
Lyra collected acoustic data continuously for 23 days on the organisms in the water-column at very high resolution, which scientists are now using to learn more about zooplankton and fish populations around the UK.
Traditionally, such techniques have required the use of survey vessels, but Cefas technologists have integrated equipment on to the Wave Glider to explore the possibility of using new platforms to complement ship-based monitoring. According to Cefas this could, in a long-run, offer value for money and more comprehensive measurements to understand the marine environment.
As with previous missions, Lyra was also fitted with a Cefas ESM2 data logger, which collected information on the physical properties of the sea surface including salinity, temperature, oxygen, fluorescence, turbidity and solar irradiance data at five-minute intervals. These data will be used to study the oceanographic features of this dynamic area. Lyra was also fitted with a meteorological sensor recording wind speed and direction, air temperature and barometric pressure, which will be used to estimate sea state and thus the performance of the acoustic system under different weather conditions.
Preliminary results suggest that evidence has been captured of diurnal (day-night) vertical migrations of zooplankton and other organisms in the water column, as well as schools of fish. At the start of the deployment, net samples of zooplankton were collected aboard the RV Cefas Endeavour, which will be used to help identify the organisms that are acoustically detected.
A second AlterEco mission is planned to start in mid-August. For this, Cefas engineers are assessing the feasibility of integrating the echosounder into Lyra’s computer system so she can transmit summary data over the satellite communications link and offer the ability to change pre-planned mission setups when required by Cefas scientists.