Wednesday, September 2, 2009

Close again -- then sudden winds

Today we were tantalizingly close again and had an excellent, four-hour focal follow of an adult male and adult female Cuvier's beaked whale (seen here from the tag boat during one of several close approaches). Note the prominent scars marking the male (top), which are thought to result mainly from fights with other males, and the absence of these scars on the female (bottom). The higher winds we had feared from the forecast held off quite a few hours beyond what was predicted and we had outstanding conditions for much of the day. We have quickly figured out where to locate Cuvier's beaked whales in this area (along the 1500m depth contour on the edges of canyons has been the best) and we soon found multiple groups of animals again. We passed up the first group because it was a mother with a small calf, but then found a good candidate group and began to track them.

The image to the left shows a sequence during today's focal follow. It is a bit of a complicated figure (you may need to blow it up a bit) with a lot going on (there was!). But it is a great example of how we can use all our tools to follow animals that dive for over an hour to great depth and then re-spot them at the surface and track them for hours. The sequence began with the ship in the northwest (upper left) corner of the figure and moving along at 6 knots (note the orange dots showing our position being spaced further apart than the rest of track where we were going slower). As we moved to the southeast, the group of two adults was spotted visually during their brief surface intervals. The red symbols with "A" and "B" labels are multiple positions of the same two whales during two surfacings in the same general area. After the animals went down on a deep feeding dive, we passed their spot and dropped a sonobuoy to monitor near that location (small circle with crosshairs along our track). We then moved around the spot monitoring with multiple arrays of listening sensors towed slowly (note our orange position markers being closer together) and began tracking them acoustically. The red circles on our track indicate when the acoustics team heard beaked whale clicks (the bigger the circle the stronger the sounds) and the purple lines show the direction from which they think the sounds are coming. We moved slowly along and kept the group on our port (left) side with very consistent detections - and the acoustics team could even tell that it was two animals. As we approached 30 min of clicking we felt confident enough of where they were and where they would come up that we deployed our tag boat and positioned them accordingly. When the animals re-emerged (positions C1-C5), we had our tag boat about 500m away, despite the fact that the animals were down for 79min and had moved 1500m in directly the opposite direction we had been traveling! As you can see from the increasing number of the "C" sightings in clusters ("E" was another single animal) we moved with the group over multiple other surface intervals between the multiple "shallow" dives (shallow is relative for beaked whales since they can be over 500m) that the animals do before deep feeding dives. The tag boat had several excellent chances, but the animals banked away several times in the last few moments before the tag could be attached. Eventually the group went on another feeding dive and we tracked them again by listening and had a bead on where they would surface. Just at that time, though, the winds tripled very suddenly (we saw the wind line coming) and the tag boat had to be recovered.

We have just a few more days at sea on MED-09 and remain hopeful we can get a few more chances like this and can have the sustained conditions needed to get that last few meters to attach one of the tags and conduct the sound exposure experiment. The weather for tomorrow does not look great, but possibly workable, and we are now fairly confident of where to find beaked whales in the Tyrrhenian Sea when we have the right weather.