Beaked whales are very difficult to sight at sea. Their blows are seldom visible, they can hold their breath on a dive for 1 - 1.5 hours, and when they do surface it is for a short time. When beaked whales were first tagged with acoustic recording tags in early part of this decade, we learned that they make deep dives to almost 2 km deep, over one mile below the sea surface to feed on deep prey. Once they reach a depth of a few hundred meters, they start to produce echolocation clicks that are so high in frequency that they are barely audible to our ears. These clicks are short upsweeps that are different from the sounds of any other marine animals, so when we hear their clicks, we can know their is a beaked whale around. The whale directs most of the sound energy forward, like a flashlight beam, but some of the energy goes in all directions. When you are several kilometers from a clicking beaked whale, when the whale sweeps its beam past the hydrophone, the phone detects several clicks getting louder as the beam points towards the phone and then fainter as the beam points away. The photos show the hydrophones, or underwater microphones, that CIBRA from the University of Pavia provided for this project. They are designed to be towed from the ship.
In the past few years, scientists have learned to tow hydrophones and use these short scans to detect beaked whales on surveys. But Med09 needs to be able to listen to most of the clicks from when a whale starts clicking to when it stops. The Pavia towed hydrophone system uses 4 hydrophones that can tell us whether the whales are forward or behind us, left or right, so we can steer towards them. Today was the day that we used this ability to follow beaked whales during a dive and to link sightings with acoustic detections. Once we heard faint scans from a group of beaked whales, we approached it and started circling the group. Once the clicks stopped, we notified the visual observers to get ready for the whales to surface. The observers then sighted a group of whales where we expected them to come up, and we picked up clicks on the next dive. By circling the whales with a radius of about 500 m, we were able to hear clicks more or less continuously until the whales stopped to surface again. This capability was an important part of our study design, so we were very happy to show how well it could be achieved with the towed hydrophones.
The weather conditions were ok but not excellent for tagging. We put the tag boat out twice to follow and attempt to tag beaked whales, but the taggers were not able to approach whales close enough to do so. Tagging beaked whales requires a small boat being able to approach to within about 12 feet to attach the tag using a pole. We are hoping for better luck tomorrow.
Today was predicted to have moderate winds. At first light, it was clear that it would be too windy to try to find and tag beaked whales, so we decided to work with pilot whales. As luck would have it, we heard distinctive sounds of pilot whales by 0700 and sighted them by 0800. One of the unusual things about pilot whales in this part of the Mediterranean is that they seem fascinated by ships. These whales came right over to the Alliance and inspected it, then swam along surfing in the wind-driven waves, following the ship for some time. We deployed the tag boat, which took photographs to identify individual animals, and attached tags to two adult female pilot whales. Unlike beaked whales, which are extremely difficult to find and approach for tagging, pilot whales are quite easy to follow and approach. In fact these whales approached the tag boat and the first whale was tagged within five minutes of the tag being readied for attachment. The tags attach to the smooth skin of the whales with four suction cups, and are attached using a long carbon fiber pole that you can see lashed to the port side of the orange tag boat. The whales showed little reaction, continuing to swim near the ship. The pilot whales form sub-groups that are usually well defined, although the subgroups will merge and separate at times. Adult males can be distinguished from adult females, and many females in these groups had calves, including neonates so young that fetal creases were visible. Under the conditions of our research permit, we did not conduct a sound playback with these groups, but we collected fascinating baseline data with bouts of complex vocalizations alternating with periods of silence. We tracked the tagged whale for more than six hours. After the tag released from the whale, it floated to the surface and broadcast a radio signal that we can use to recover the tag. Once the tag is recovered, we connect it to a computer and download the data before we can explore it.
