Wednesday, August 19, 2009

Calmer Seas -- Many Animals

Today dawned calmer with light seas and winds between just 5-10 knots for most of the day dropping to almost zero by late afternoon and evening. These are the conditions we need to reliably sight and tag beaked whales. Throughout the day we sighted many cetaceans, including hundreds of common, striped, and Risso's dolphins, pilot whales, and about 8-10 different groups of Cuvier's beaked whales. Both teams monitored the vast horizon and the cacophonous underwater acoustic scene these animals covered, trying to find the right situation. Several times our acoustic teams were hampered in extracting the beaked whale clicks from similar vocalizations from other nearby species. Also, almost all of the groups of beaked whales we found today either had small calves or were single individuals, which meant we could not work with them for different reasons. We did follow two different (we think!) groups of adult animals near the end of the day as good candidates, but despite the flat seas, visuals, acoustics, and tag boat in the water, they gave us the slip.

The figure you see here shows a bit of our track from today and gives you a sense of the relative movement of the animals and some of our tactics in using different sensing gear in monitoring their movement and behavior. The orange line shows the movement of the vessel starting at the southern edge of the plot (note the depth contours in meters along the track). The crosses with numbers 1-10 show different positions of a real-time, high-frequency GPS sonobuoy we dropped early in this encounter. These locations are over about four hours and if you noted the sonobuoy tracks from the blog several days ago you can appreciate the quite different current conditions we encountered today. The red triangles are sequential positions and headings of the focal group of beaked whales we were tracking. The triangles of other colors are sightings of other cetacean species and the little boat symbol is the position of our inflatable tag boat. As you can see, the animals increasingly tracked to the north and then the northeast (away from our first sonobuoy) and we monitored them from some distance, relying entirely on the visual team to track them since they are silent during the surface diving interval. When the group went for a deep (~1000m or more) dive after the last red triangles, we dropped our towed arrays back in the water and initiated a large circle around their position to monitor for their clicks. You can see some orange symbols along the Alliance track during this circle, showing that we successfully detected the animals with expected bearings during this period. This plot shows the complexity and integration of the visual and acoustic capabilities we have here, how they complement one another to enable us to monitor deep-diving animals in real-time, and the importance of real-time GIS visualization to guide our decision making in this challenging task.

The forecast for tomorrow and Friday is for excellent conditions such as we had today followed by possibly high winds over the weekend so we are all very much focused on the window the next few days looks to hopefully afford us.