Fins, Brief Winds, and then Ziphius

The weather was good for the most part today as we worked through an area where Cuvier's beaked whales had been seen from ferries and a few sightings from other researchers. We covered a lot of water during the day and found a lot more marine mammals than the area covered yesterday.

Our first sighting was a group of three fin whales and throughout the day we would have more than 20 sightings of other groups or individuals. We saw several fin whales breaching, which is an impressive sight, and had several within a mile or less from the boat. There were also several large groups of dolphins leaping and skimming the water around us several times. The speed and maneuverability of these sleek animals never ceases to be amazing. After seeing the fins in the morning, the middle of our day was briefly interrupted by a small storm cell that we watched form over the sea and then move past us. The wind kicked up for about an hour and we had to stand down our visual team briefly. It actually rained for a few minutes, which we haven't seen for a long time, but it passed quickly and we could again work.

By mid-day the conditions were workable again and we continued searching for beaked whales. We found a group of three and our visual team guided the tag boat toward them. It was good for all to be back on our focal species again after the transit over and two days of searching here. We followed them through a number of surface intervals and the tag boat had two close approaches with reasonably good chances at tagging, but the animals then went down for a deep dive and again we ran out of daylight. The weather predictions for Tuesday look outstanding and we will begin in the same area where we had our first successful focal follow here.

Searching...

Today was spent searching widely across our new operating area -- in search of suitable wind and sea conditions and, once we found those, in search of beaked whales. The day dawned rougher and windier than we expected from the forecasts, but we had a clear picture of where to find better seas. By mid-morning we worked into relatively calm winds and workable swell conditions and began running across some of the steep drops and seamounts on the bottom of this once-volcanic area. For the rest of the day we had relatively good viewing conditions and we worked at speeds where we could monitor as much area as possible using both our visual and acoustic teams. However, somewhat surprisingly to us, we didn't see a single beaked whale today and heard just one sperm whale on a sonobuoy. There were the occasional striped dolphins and a few sea turtles, but relative to where we were yesterday, this area was relatively devoid of marine mammals.

We have quite a lot of other promising looking areas to cover and the wind and wave forecasts for tomorrow are promising. We will try and work in an area where there have been some incidental sightings of beaked whales from ferries.

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.