Sperm Whale Central

We were all very happy today to be back on effort and for much of the day in very calm seas. After a short pit stop at dawn to restock with some supplies we began searching for marine mammals in our new operating area. Shortly thereafter we spotted a mother-calf pair of Cuvier's beaked whales. This was encouraging since the area where we are now has not been systematically surveyed and, despite some anecdotal observations and promising bathymetry (bottom features), we weren't sure what we would find. We subsequently ran across quite a bit of marine life, though not our primary focal species. We came through a cluster of loggerhead sea turtles, found patches of striped dolphins, and heard Risso's dolphins chattering away. But the mammals that would dominate our day were deep-divers like beaked whales.

Our first sperm whale sighting, which was in water about a mile (1.6 km) deep, was followed over the next eight hours by 19 other sightings of other (mainly) individuals or groups. We recorded a total of 26 individual sperm whales sighted. As with our other observations, we could have re-sighted some of the same animals more than once, but since we were moving at 10 knots in one general direction for much of the day to cover a good amount of water in this new area, most of these were probably different animals. We saw several sperm whales breaching and heard them on our acoustic arrays much of the day, but never saw any close enough to the boat for good pictures. It is a promising sign that we are seeing other deep-diving, primarily squid-eating marine mammals (like beaked whales are) and it is also interesting to observe such relatively high densities of sperm whales in this area.

The weather outlook for tomorrow is relatively promising and we are refreshed to be back in water that is more amenable to our objectives than what we left in the Alboran Sea; we hope to locate more beaked whales (and fewer sperm whales). Throughout this project that we have been treated to some fantastic sunrises and sunsets on the Mediterranean Sea, such as this one from yesterday.

Eavesdropping

We have been steaming for 48 hours now and are nearing our final operational area. The winds were a bit lighter for part of the day today as we moved further away from the north African coastline, but as got into quite deep water we did not see a great deal of marine life. Several sperm whales, dolphin groups, and a sea turtle were spotted throughout the day, however, as we came through these poorly-studied waters. As we did during our transit yesterday, we have used this time to process the large amount of biological, oceanographic, and acoustic data that have been obtained thusfar.

One of our primary tools in eavesdropping on the underwater acoustic scene to locate, identify, and track marine mammals are arrays of hydrophones. With these listening sensors towed behind the vessel (you can see one being deployed here), and with the expert acoustic observers we have to fine-tune measurements and interpret what we are hearing (and also seeing on special displays), different species can be discriminated and estimates of signal strength (to give a sense of near or far) and bearing to calling animals can (sometimes) be made.

There are two arrays of hydrophones towed in parallel behind the ship, one on the right side, one on the left side. Each array is composed by a 150m long towing cable (which can be extended to 300m) ending with a 12m long oil filled tube that holds two wideband acoustic sensors each and their preamplifiers. The electronics onboard amplify the signal to be digitized with a 4 channels AD converter at 192kHz sampling rate connected to a powerful computer with dedicated, custom software designed for both research and mitigation purposes.

This software allows us to acquire, record to disk, analyze and display up to 8 channels in real time. A high resolution spectrographic display (a picture of the sound showing frequency, or "pitch", over time) shows all the features of the incoming sounds, even those we can't hear, because they are too high in frequency or too brief for our ears to detect. Several examples of the kinds of recordings made with these specialized listening sensors and processing software are given here; these are of long-finned pilot whales and striped dolphins recorded recently in our research.

» Listen to Striped dolphin clicks shown on three channels (note 24kHz zoom on top channel)

» Listen to Pilot whale bursts and whistles with harmonics

A special directional display shows the signals coming from the two arrays (4 hydrophones) to provide intuitive cues as to the direction of incoming sound. By using these two displays, researchers can recognize sounds coming from different species and estimate the direction from which they came. This information is especially important in the current research project to position the tag boat as close as possible to the position where the diving animals are supposed to emerge at the surface.

Tomorrow morning we will be back on effort in our new operating area. The weather forecast is quite favorable for the next several days, while it remains quite poor for the Alboran Sea area we recently left. So, we embark on the last week of our collective efforts here with renewed hope and optimism for favorable seas and accommodating whales.

MED-09 Oceanographic Measurements

Today was the first of two days transit to our new operating area in the Tyrrhenian Sea. We continued both visual and acoustic observations while traveling and were quite interested in what we might see or hear because the areas we are passing through have not been well-studied. Some dolphin groups were detected, but not much else. We had reasonable seas and the wind was just 10-12 knots, but it was straight from the east and on our bow so effectively closer to 20 knots which made things tough for the visual team. As we transit, we continue to process all of the biological and oceanographic data that have been collected thus far.

An important and interesting kind of oceanographic sampling that is being done is to measure different properties of sea water at various depths in areas where we have been operating. We use a device to measure the conductivity (a proxy for salinity), temperature, and depth (measured with pressure) of the water (called a "CTD"). Measurements are made by lowering the CTD slowly in the water column to provide real-time data about biologically-important ocean parameters. The CTD has two salinity probes, two temperature sensors, and one pressure sensor; it passes through and samples the water for these parameters at approx one meter/sec. It also operates a pumped system from the different sampling tubes seen in the picture here to guarantee that the same sample of water is measured at specified times. Additionally the Alliance CTD includes two sensors, which directly measures the oxygen content in the water column. In this way we can fully characterize the oceanographic parameters of the water column and can also calculate how sound travels at different depths in real-time using the salinity, temperature, and depth information.



In the images here you can see four different plots from a recent deployment of the CTD to 1000m, each of them showing a different measurement with increasing depth (downward on the plots). The temperature plot shows the much warmer surface water and colder deep water; note that below about 200m there is almost no change in the ocean temperature here. The salinity trace shows another common pattern in this area which is fresher water near the surface and saltier water with depth. The oxygen plot shows higher levels near the surface (where waves mix the water) and lower levels deeper. Finally, the sound velocity profile resulting from the other measurements shows more rapid sound speed at the surface and deeper, with a minimum sound speed around 150m. Like light, sound bends to areas where it travels more slowly and the minimum seen here is called a "sound channel" that would tend to carry sound greater distances than where the sound velocity is higher.


By making these measurements in different areas of interest, and at depths down to 1000m (over 3,000 feet), and comparing them to where we see and hear different marine mammals, we can get a better sense of which kinds of environmental conditions are most important for different species. Additionally, the sound velocity profiles are useful in predicting broadly the underwater sound fields during controlled exposure experiments using real-time oceanographic measurements; these are also directly measured at different places with other sensors (e.g, acoustic tags, sonobuoys).

Still Rolling

The winds gradually came down from the gales of last night throughout the day, but the swell from the sustained strong (Beaufort 7) winds remained prohibitively high for us. Our visual observers went on watch several times as we looked for pilot whales. We did find some, but with the seas and the fact that most of the sub-groups had small calves, we did not attempt to attach acoustic tags. As usual, we had our passive listening arrays deployed and had intermittent detections of marine mammals at different points during the day.

Overall it was another day where the weather prevented us from achieving our primary objective. Based on our experiences the last few weeks and the wind and wave forecasts for the next five days, we will be leaving our current location and transiting to one of our other large operating areas closer to Italy. Thus, the next few days we will be in fast transit survey mode as we cover a large amount of ocean. We will listen with one array in the water and conduct visual surveys as the conditions allow. The area we will be passing through has not been surveyed systematically and thus even as we transit through this area we hope to provide some useful contributions to the scientific understanding of part of the western Mediterranean Sea.

Rough

The wind blew steady all day today from the west at 20-25 knots with gusts to 30, building heavy swell. The combination of Beaufort 6-7 winds and resulting seas was way beyond what our visual or tag team could work in for any species and they were not placed on effort at any point today. We did continue to monitor acoustically, while holding on, and covered some interesting-looking areas. But even our acoustics team was affected by the conditions to some extent with the rough seas and had limited detections.

We are hoping for better wind conditions at some point tomorrow as it changes from the west back to the east, but we know we will still be dealing with residual swell from it the strong and steady winds today. We are having strategic discussions about our next course of action.

Hot Spot

Our read of the weather was right on today. We had excellent conditions in the morning, workable weather in the middle of the day, and strong winds by mid-afternoon. As has been the case every day we have been in beaked whale areas with suitable sea conditions, we saw many animals today. If you look closely at the picture here you can see the three different sizes of binoculars we use to monitor visually at different distances. Initially we were spotting just single animals, who are very difficult to tag relative to groups, and we kept moving. Soon, however we came into an area with many different groups.

It was difficult to track who was who and how many groups there were because it seemed very likely that some of the groups were splitting apart and re-forming in different configurations while traveling in the same general direction. Some of these groups had calves, but generally speaking we were seeing more large and workable animals. With the excellent conditions, we soon got a good read on a group of four animals without calves. We followed them through several surface intervals and "shallow" dives and had a good bearing on their direction. The tag team had two close approaches to within about 10m of the animals (the picture here is of the focal group during one of these approaches), but was not able to attach one of the DTags to the animals. We continued to track them as they went into a long, deep foraging dive and began producing echolocation clicks, using our listening assets. As yesterday, with the integrated information on bearing from the visual teams and acoustic bearings from the listening arrays, we felt quite confident that we maintained them on our port side and had a probable zone where they would resurface. Also like yesterday, however, as we positioned ourselves like this and were ready, the winds came up quite rapidly to 20 knots and we were forced to break off the search. We continued to search for pilot whales in the marginal conditions and ultimately found a moderate size group - using acoustic cues since the wind caused poor visibility. However, there were small calves in their groups and both that and the sea state would have prevented a CEE with them as well, so we did not attach pilot whale tags.

The weather forecast for tomorrow looks poor with strong winds from the west; Wednesday may offer us another window of calm as the winds shift back to the east. We will, of course, be ready to go tomorrow if the forecast is incorrect, but if we cannot look for beaked whales visually, we intend to conduct acoustic surveys over what looks to be an interesting seamount and submarine canyon area that has not been extensively explored. Once we have good conditions again, we will likely return to the area where we worked today. Even accounting for likely re-sighted animals, a conservative estimate of the number of individual Cuvier's beaked whales we saw is about 20 within about a 60-square-mile patch of ocean -- quite a high density for our newest "hot spot".

Chances early...then more of the same

Today dawned much calmer than expected and we were on animals both visually and acoustically quickly. We searched around our first beaked whale acoustic detection and soon thereafter had a visual sighting. We also crossed paths with a large group of common dolphins (50 animals or more), saw some large Risso's dolphins riding on the bow of a nearby large ship, heard pilot whales, and saw a large tuna leap several times in the air with a large fish in it's mouth. We followed one promising group of three adult/sub-adult Cuvier's beaked whales, tracking them both visually and acoustically (see below), and had our tag boat over the side and ready to go. But we hadn't managed to tag them by about 1100 and the wind picked up from the east again rather quickly and by noon we had the Beaufort 5 conditions described yesterday that were predicted for today. We continued searching for pilot whales, but by mid-afternoon the winds again ended our day early.

During the mid-morning focal follow on the beaked whale group, we demonstrated again an effective capability to integrate information received from our visual and acoustic teams to position the ship relative to animals while adjusting for other environmental factors as well. In the figure here, you can see the track of the ship as the orange symbols in a line beginning in the southwest (lower left) section of this GIS plot; the closer together the symbols the slower the ship and the further apart the faster the ship. As we moved to the northeast, we had a visual sighting (red C1) of a beaked whale, identified as a single animal. We continued forward and had a subsequent acoustic detection of beaked whales (seen as the pink circle on top of the ship's track) and an approximate bearing to the animals ahead of and to the starboard (right) side. About 25 minutes later we had two good visual sightings of a group of three beaked whales (red C2 and C3) at the surface and had clear direction bearing (heading) for them to the northeast (direction of arrows). The animals then did a shallow dive that we expected would take another 15-30 minutes. Now we had a choice - and a problem. It was still morning at this point. The sun was coming up in the southeast and there was a serious glare on the sea that would prove difficult for our visual observers if we did not adjust the position of the ship relative to the whales. So we turned toward the sightings, sped up significantly (note the orange symbols spacing out), and cut behind them while maintaining acoustic detection. This maneuver worked perfectly as we passed them and then slowed down, turning to the north while continuing to hear them now off our port (left) side (additional small pink circles along ship track). The two purple lines show two of the acoustic bearings which predict direction to the animals underwater; they are close enough in time that where they cross is an estimated location. Using the sighting location, visual bearing, and these acoustic bearings, we had a good prediction of where they were and where they might come up. Now we had the sun on our stern (back) and also a better orientation to the significant current from the east as well. Ultimately we were precluded from seeing them come up despite, being in an ideal position, because throughout this maneuver the wind jumped from 5 to 15+ knots. Nevertheless, this kind of fairly complex tracking with integrated visual and acoustic information - reading the animals using these tools and orienting ourselves correctly relative to the sun and the current - demonstrates that everything is working together quite well.

The wind is dropping this evening and we hope to catch a nice calm window tomorrow as the wind switches from the east to the west. If we get flat seas we know the animals are here and that we are ready.