Tagging at sunset

How much light do we really need to tag a couple of whales?

Around 4 in the afternoon, we had been enjoying a fresh squeezed orange juice while working in a cafe. Tired after a couple days on the water, we were mentally making a list of all the things we had to do before going out to sea at dawn the next morning. It was the last week of our trip, and as our expedition was drawing to a close, we were looking forward to heading home and analyzing the data we had collected.  All of a sudden we received an unexpected call from our captain Philippe, informing us that the wind had just shifted and that we could take an evening trip out into the Strait.

A large long-finned pilot whale newly
instrumented with its own DTAG

Weather windows in the strait are few and far between, so we seized this opportunity. Usually we prepare for a few hours the night before a deployment and then for another hour or so in the morning, but we didn't have long before dark, so we raced home and assembled everything as quickly as possible - tags, tracking equipment, cameras, radios, food, water, warm clothes and coffee… the list is long, but by this point we know it by heart.

An older juvenile surfaces just before being tagged

We drove to Algeciras where our boat had been moored during a strong easterly wind and got underway as fast as possible.  Algeciras is a more sheltered moorage than Tarifa, but it also takes much longer to get to the whales' known habitat.  It would be at least an hour and a half before we could really begin looking for whales and sunset was fast approaching. 

Finally, we arrived in deep water where the whales were usually found. As the sun dropped towards the horizon, we were all eyes, trying to spot the faint blow of a pilot whale in the distance, or the slight reflection of a dorsal fin. With no luck, we were resigning ourselves to return to Tarifa and head out at dawn the next morning. 

Night descends on the Strait

Then, just as the sun set, we were joined by a group of very curious pilot whales, many of them younger juveniles. Whales in the strait often have to swim fast to fight the strong currents and maintain their position, but these animals were bow-riding off Elsa and almost asking to be tagged. Philippe quickly verified that all the animals were resident individuals and we identified a female and older juvenile that seemed to be a distinct sub-group. With the whales in a friendly mood, things went really fast, and just as darkness descended on the strait, we had two tags sitting on our chosen animals and the regular beep of their radio transmitters to take us away into the night.

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Nicholas Macfarlane and Frants Jensen 

Common dolphins

The only thing worse than being stuck in the Bay of Algeciras waiting for the fog to lift is discovering that in our rush to leave we mistook salt for sugar in our iced coffee.  The saving grace is that the bay is completely filled with common dolphins. 

The weather has been quite unpredictable over the last few days.  We've gone out to sea, but fog or high wind has kept us from being able to work with the pilot whales.  Instead, we head to the Bay of Algeciras, next to Gibraltar, where CIRCE is collecting photo-identification data on the dolphins who live there.

Aixa Morata (front) and Mar Hernandez (rear) taking
photo-ID pictures of a short-beaked common dolphin

A fundamental issue in marine mammal research is being able to recognize individual animals.  This allows you to address basic issues such as where and when animals have been sighted or what animals they regularly associate with.  This information also enables higher level studies of population dynamics such as population size or birth and mortality rates.

One way to identify individual animals is through photos of distinctive features.  We often recognize humans by photos of their faces, but different species require different body parts.  With humpbacks and sperm-whales, we use tail flukes, and with pilot whales and dolphins, nicks and notches on the dorsal fins and scars on the back allow us to discriminate between animals.   

A group of short-beaked common dolphins

In the field, this means taking high-quality time-stamped photos of dolphin and pilot whale dorsal fins and comparing them to a catalogue of known individuals to identify the animals.  Unlike in many parts of the world, most of the pilot whales here are surprisingly well marked, but others have very few markings and are extremely difficult to distinguish. Over the last 13 years, CIRCE has built up a long-term catalogue that enables identification of nearly all the resident and immigrant pilot whales in the area.

A close up of a dorsal fin from a long-finned pilot whale
allowing for photo identification

This is why we are here. The information CIRCE has collected is crucial for our studies of social dynamics. We rely on identifying animals in the field so that we may select highly associated individuals - individuals that are seen consistently together - for tagging. Toothed whales are very capable vocal learners, and it is likely that they change their calls when associating with specific individuals for long time periods. The way animals interact within a social group is also likely to differ depending on whether animals grew up together or not. Thus, the long-term data on association patterns available here may help us interpret datasets.

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Nicholas Macfarlane and Frants Jensen

A 3D stereo geocoding system

Nicholas Macfarlane localizes whales in space and time
with a new 3D stereo camera geocoding system

The 3D geocoding system merges images from the left and right
cameras to precisely position the animals. Examples of calculated
inter-animal distances are shown on the left image

How to track a group of free-moving, diving animals?

Social animals like pilot whales often manifest many of their behavioral dynamics, such as reactions to stress or disturbance, through changes in their relative movement and position. Many social animals group more tightly together when they feel threatened.

Therefore, some of the key pieces of information that researchers try to collect are measures of group cohesion that capture these spatial changes.

But there's a problem: in practice, this is mostly done by eye and it's really hard  to do in a quantitative way.  Imagine that a group of whales surface for an instant before diving back down.  Precisely estimating all the inter-animal distances in that moment is extremely difficult, particularly if the group is large and not right next to the boat.

Working with Jonathan Howland of WHOI's Deep Submergence Laboratory, we've developed a 3D geo-locating system designed to address this problem.  It uses a GPS that tells you where you are and a 3D attitude sensor that tells you the direction you're looking.  Then, just like your two eyes estimate depth perception, two cameras merge together to very accurately measure distance.  All of the information is combined together by custom software to give us quick, easy and accurate positions of anything we can take a picture of. 

Now we can use this system to precisely document detailed behavioral reactions to disturbances such as man-made noise or sonar.

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Nicholas Macfarlane

Eavesdropping on a foraging pilot whale

The world of a deep-diving toothed whale is hard to imagine. However, it is even more challenging to imagine how the whales themselves perceive their underwater environment.

Frants Jensen analysing data from a
recently tagged pilot whale

Toothed whales depend on echolocation sounds for orientation and foraging. They send out high-amplitude, highly directional biosonar signals but have to listen for the tiny fraction of sound energy reflected off prey and other objects. Foraging requires both detecting and discriminating the faint echoes from prey through background noise but also closing in on and capturing prey up close.

The beauty of echolocation-based foraging is that we can use acoustic recording tags to eavesdrop on the foraging of tagged animals such as sperm whales or beaked whales, effectively tapping into their own biosonar system.

A time-frequency representation (spectrogram)
of a foraging buzz produced during prey capture

Like other toothed whales, pilot whales switch from relatively slow clicking when searching and approaching prey, to periods of very fast clicking (a foraging buzz) when they get close to prey. These periods of rapid buzzing can be used for identifying when or where tagged animals forage. This information can also be combined with the other sensors of the tag to identify specific kinematic maneuvers during prey capture, or determine whether prey was captured.



Listen in on a pilot whale while it searches for and captures prey

Here, we have taken a dive profile and marked down the different foraging events using some of the auditing software developed for these DTAGs. Five different sequences (labeled A to E) can be listened through by pressing the corresponding button:

A: Pilot whale starts searching for food using regularly spaced echolocation clicks.
A: Play sound

B: First foraging buzz in this deep dive.
B: Play sound

C: A handful of foraging buzzes occur near the bottom of the dive, some of them quite long, possibly indicating prey chases.
C: Play sound

D:  On its way back to the surface, the pilot whale is mostly silent, but occasionally calls out for group members.
D: Play sound

E: As the tag breaks the surface of the water, the animal catches its first breath of fresh air in 14 minutes.
E: Play sound

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 Written by Frants Jensen

Data

A DTAG sits on an adult pilot whale, ID#248

Dive record of a tagged adult pilot whale

Imagine diving down to a depth of 800m.  

It's extremely cold, ambient pressure is 80 times higher than at the surface, and the only trace of light is given off by small bioluminescent organisms.  Now try to find a dozen decent-sized meals, all while holding your breath for 15 minutes.  A typical pilot whale will do this many times in a single day.
 
Using our tags, we can study this foraging behavior in great detail.

The suction- cup DTAGs that we deploy not only capture acoustics but are also equipped with sensors that measure the 3 dimensional movement of the animals and their depth.
 
Here is an example of one of our large tagged adult pilot whales, ID# 248.  As you can see in the figure, this animal was making deep dives down to the bottom of the Strait, likely foraging on prey such as  squid that they hunt with their echolocation clicks.
 
We know from studies of the stomach contents of stranded pilot whales that most of their diet is composed of squid, but we have very little idea of when, where and how often they capture these prey.  The sensor data from the tags we deploy gives us a window into the basic ecology of these echolocating predators.  With multiple simultaneously tagged animals we can even see how the whales are interacting at depth and whether they are foraging in the same place or at the same time.

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Nicholas Macfarlane

An unexpected bonus

The dangers of the Strait

Long-finned pilot whales, like other marine mammals in the Strait of Gibraltar, face a host of potential threats to their health and well-being. 

What kind of risks do pilot whales face?
A pilot whale with a large, fresh wound next to its dorsal fin

Traffic here in the Strait can be intense, with risks of ship or propeller strikes combined with elevated noise that may hinder the communication and foraging of these animals. 

Heavy recreational fishing in the area adds risks of interactions with fishing gear, and industrial pollution of the Mediterranean waters poses risks of toxic compounds such as heavy metals building up across the food chain. 

In addition, the whales have to navigate natural threats, and - just like the rest of us - they occasionally get sick.

The morbillivirus outbreak

Curro, a resident pilot whale of the Strait that was injured by
a ship's propeller in May 2008, but is still going strong

From October 2006 and throughout April 2007, the population of pilot whales in the Western Mediterranean was hit hard by a massive morbillivirus outbreak. Cetacean morbillivirus is a virus closely related to canine distemper virus and also human measles, and it can be highly lethal.

A large part of the pilot whale population in this area disappeared over the course of the next handful of years. This has caused a lot of social restructuring, with most pilot whale groups reorganizing themselves by merging with other individuals. Fortunately, CIRCE has collected extremely valuable data over the last 13 years, documenting these changes as they were happening.

An unexpected bonus

As it turns out, the group we tagged on the 8th happens to be a truly exceptional study group: These animals have been observed consistently together over the course of the last 13 years that CIRCE has been operating, and have escaped relatively unscathed by the morbillivirus epidemic. The social interactions we observe in this group of animals will therefore be a valuable piece of information for understanding how pilot whales that have grown up together coordinate behaviors and interact with each other.

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Written by Frants Jensen

Success!

A neonate pilot whale passes by the boat

Dtag on 1 of 4 long-finned pilot whales in our group

It was a really difficult call to make.

It began as a perfect day.  Leaving the harbor at first light, the gentle winds kept the fog at bay. Throughout the morning, we found a couple of larger groups of animals, some of which we had tagged during previous expeditions to the Strait.  Too big for our current investigations, we cautiously took photo ID pictures and left the animals to their frolicking.  

In one group we even spotted a tiny neonate (a newborn pilot whale) that could not have been more than a few months old.  We don’t work with groups containing neonates for fear of disturbing them during such a vulnerable stage in their lives. 

After a few hours things began to go downhill.  We found ourselves on the extreme Eastern edge of the Strait; there were no pilot whales in sight, and this far East it could be a long time before we found new ones.  The waves were also picking up.  A strong storm was forecast for the evening, and our narrow weather window was closing.  With sagging spirits and an exhausted team, we needed to decide whether to return to port or struggle back westward through the heavy currents.

We chose to push on for a little longer, and thank goodness that we did!  Within an hour, Philippe pointed out the next group of pilot whales in an unexpected calm patch of water. These animals were playful, with an older juvenile quickly coming in close to investigate our boat. We held off approaching the rest of the group while collecting 15 minutes of behavioral observations from a distance. Then we maneuvered slowly towards the animals – and suddenly, the words “Tag on, tag on” rang throughout the boat. One of our tags sat neatly right in front of the dorsal fin of a big, adult male! This male was with three other animals including the older juvenile that had inspected our boat, and within 90 minutes we had tagged all of them!   As the last tag was placed on the juvenile, we all take a quick moment to celebrate. 

After 6 hours of fantastic behavioral observations, our tags released perfectly as programmed.  We carefully homed in on the radio signal for each tag and fished the valuable data out of the ocean. We retrieved the last tag and headed into the port of Algeciras just as the sun was setting on the Rock of Gibraltar.

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Frants Jensen and Nicholas Macfarlane