As wave and tidal devices are deployed in coastal waters and estuaries in countries around the world, there is intense interest in understanding how marine mammals, sea birds, fish, and sea turtles may interact with the machines underwater. Will animals be at risk from rotating tidal turbine blades? Will they be attracted to the foundations, anchors, and devices? Will they sense the mooring lines and avoid them? All these questions have prompted researchers to explore effective methods for viewing interactions between animals and a variety of tidal and wave energy generating devices. Active acoustics, sometimes called underwater sonar, are among the key types of instruments that researchers are using to “see” animals in close proximity to devices.
Active acoustic devices produce streams of digital data that researchers must interpret. Mathematical formulas, called algorithms, are developed by scientists to modify the electronic signals from the active acoustic devices into numbers and graphical outputs. These outputs still require additional interpretation by scientists to determine what the acoustic “targets” represent. In addition to the challenges of deploying and operating sensitive acoustic instruments in high energy areas where animals may encounter tidal or wave generators, there are many sources of noise that can interfere with the digital data collected. The noise sources include: reflections from bubbles in the seawater; turbulence (water moving chaotically due to rapid changes in pressure and velocity); vibrations from the wave or tidal device; sounds from the research vessel or from other boats in the area; and reflections off the seabed. Researchers from several countries are actively investigating and collaborating on different approaches to filtering acoustic instrument data, correcting or eliminating data that masks the presence of marine animals, and interpreting results.
On July 24th 2014 Annex IV - the international initiative to understand environmental effects of wave and tidal development - sponsored an online experts’ forum on this topic. Gayle Zydlewski from the University of Maine led the discussion, to which prominent researchers in the field were invited. The audio and video files of the presentations are archived. Please take this opportunity to comment on the topic, ask questions of the experts, and learn more about acoustic data.