After a successful test of one of the repaired passive listening systems that had been having some problems, we conducted a drill of deploying an array of real-time listening buoys (called "sonobuoys") we will use to monitor vocalizing whales once a focal group is tagged. One of our small boats delivered the sonobuoys in a grid while we deployed the sound source for controlled exposure experiments to a depth of 75 m (but did not turn it on). Meanwhile, our visual team practiced tracking a "whale" (which was actually our own tagging boat) and we tested our ability to safely maneuver for visual monitoring with both the listening gear and the source in the water. As you can see from the plot here, we dropped a total of four sonobuoys (labelled A-D) in a counter-clockwise fashion at a spacing of about 2.5 km.
These listening devices have a relatively deep listening sensor and relay sound information using a radio signal back to the ship; with them we can monitor the area around focal whale groups during a controlled sound exposure. This figure shows one of the challenges we face here in the dynamic Alboran Sea, which is the affect of currents on free-floating buoys. Notice that various green symbols (starting from the north) moved consistently to the SSE over time (on average about 4.5 km in 2.5 hours). For instance, note the four green bulls-eye symbols furthest to the east labeled "Sonobuoy B" and the consistent drift (time noted for just this example). We know from the ship's sensors that there was a fairly strong current (almost 2 knots) in this direction, so this was not surprising to us. However, it demonstrates another challenge facing us in being able to not only read the position and behavior of the animals, but also the position and behavior of our monitoring gear in relation to the movement of the water (and other factors such as the wind and sun). Practice and drills are required to understand and manage such challenges, which was part of why we worked so carefully through it today. Ultimately we were very pleased with the timing of the operation and in our ability to monitor an area in which we and all our gear was being strongly moved in the active sea.We continued to monitor acoustically and visually for marine mammals and did manage a number of detections in both modalities of several species. Some Cuvier's beaked whales were heard early in the day but not seen and then a total of five animals were sighted near sunset. Additional detections were made of other cetaceans, including Risso's dolphins, striped dolphins, and common dolphins, although no attempt was made to tag these animals.
Unfortunately, one of the common dolphins we located had been caught in a fishing net and was floating dead in the water. As you can see from the picture here,
it had been killed relatively recently and the flukes (tail) and dorsal fin were severed, presumably by fishermen trying to remove the entangled animal without cutting their nets. We approached the carcass in one of the small boats to document the species (Delphinus delphis) and sex (female) and to obtain photo documentation and samples for genetic analysis. We also sighted an ocean sunfish floating dead and seemingly entangled and what may have also been a dead sea turtle as well. By-catch (the incidental killing of animals in fishing gear) is a serious problem for marine mammals around the world, including here in the western Mediterranean.We hope for better weather and less morbid observations tomorrow and are primed and ready to accomplish our objectives if weather and animals will allow. Knock on wood, the forecast looks more promising.
