Marine acoustics uses sounds to study the submarine environment. There are active acoustics and passive acoustics.
Active acoustics allows to “see” under water down to depths of several hundred metres, where not even light penetrates. Echo sounders emit sounds which travel and strike obstacles, including living organisms. Based on the echo retransmitted by these obstacles, their position and properties can be deducted and an image of their distribution in the water or submarine relief can be generated. At different frequencies, echo sounders can distinguish echoes originating from fish and those from zooplankton. Krill for example have a stronger echo at 120 kHz than at 38 kHz, frequency at which capelin have a stronger echo. Zooplankton smaller than krill has a stronger echo at frequencies exceeding 120 kHz.
Sound propagation in water can also be studied to determine the latter’s characteristics such as its average temperature. More powerful low-frequency sounds can be used to detect modern submarines at great distances or to explore underground structures, notably for oil prospecting.
Telemetry project on rorquals of the Estuary and acoustic prey census
© Ocean Mysteries – Georgia Aquarium
In October 3, 2013, while the GREMM team is in the St. Lawrence Estuary, the Parks Canada crew is simultaneously performing an acoustic prey census aboard L’Alliance in order to determine at what depths and on what types of prey the seven-tonne giant is feeding. The acoustic images, obtained using the echo sounder submerged in the water column, reveal schools of fish, probably sand lances, also being pursued by several other minke whales as well as hundreds of gray seals and seabirds.
This rorqual marking project is being conducted conjointly by the GREMM and Fisheries and Oceans Canada, with the participation of Parks Canada for the prey census.
Did you know that sound travels approximately four times faster in water than in the air? And that it travels much farther? Passive acoustics is the study of submarine sounds. To capture these sounds, researchers place hydrophones (waterproof microphones) under the sea. But whales can emit sounds that are inaudible to the human ear, e.g. infrasounds and ultrasounds. Hydrophones can detect them, but in order for us to be able to hear sounds below 60 Hz and above 16,000 Hz, they must be transformed. They are either accelerated or slowed down.
Here’s what a low-frequency sound emitted by a blue whale sounds like when it’s accelerated times four.
Using a network of hydrophones placed under water, we can even pinpoint the source of the sound, i.e. the location of the whale. Over time, it is thereby possible to gain an overview of the use of the territory and understand correlations with certain climatic and oceanographic factors. Lastly, this technique can be used to study the ambient noise of the sea, including natural sources (such as earthquakes) and anthropogenic sources (such as boats), and thus to assess sound pollution levels and their effects on different marine species.
Acoustic Monitoring With PAM-Equipped Gliders
How to detect whales when they spend most of their lives under the water and far from the coasts? With acoustics! Whales produce a plethora of sounds, which can be used to find out when and where they are.
Acoustic detection of whales comprises fixed array hydrophones, autonomous Passive Acoustic Monitoring (PAM) and CTD (Conductivity, Temperature, Depth)-equipped gliders and satellites for data transmission.
In Canada, Ocean Tracking Network (OTN) and the Marine Environmental Observation, Protection and Response Network (MEOPAR) are leading the use of autonomous underwater vehicles (AUVs) to collect data on marine mammals. Along with hydrophones, OTN and MEOPAR use two main types of profiling and surface gliders equipped with PAM systems:
- Wave gliders: Glide the ocean’s surface waters using wave and solar energy. These gliders transmit data in near real time.
- Slocum gliders: Capable of changing their buoyancy to dive for CTD (conductivity, temperature, depth)-profiles in the water column, these gliders have scheduled surfacing every 2-4 hours.
Cetaceans produce sounds for various reasons, including communication and prey detection. It is these sounds that the gliders record. After recording the sound, each glider automatically analyzes its spectrogram to identify the source species and transmits the data to a satellite.
Using this technology, MEOPAR is working on sending the satellite data to various maritime vessels that have signed up for alerts with the WHaLE project through the marine AIS (Automated Information System) in near real-time. This will allow vessels to take mitigation efforts to minimize their risk of collision with cetaceans by either slowing down in areas of cetacean concentrations or changing their course. The project is already underway here in the Gulf of St. Lawrence, Northwest Atlantic Ocean and the Northeast Pacific.
Additionally, researchers have also been able to characterize different habitats that baleen whales prefer.
Gliders also record high-frequency sounds emitted by krill and other prey, which allows researchers to predict movement patterns of one of their predators: the whales. It is an important step in determining management strategies, such as speed restrictions in the Gulf of St. Lawrence.
(2016) R. Davis et al., Tracking whales on the Scotian Shelf using passive acoustic monitoring on ocean gliders. Oceans 2016 MTS/IEEE Monterey, 1-4. doi: 10.1109/OCEANS.2016.7761461
(2017) Johnson H. et. al., Using Slocum gliders to characterize baleen whale habitat. Presented at the Society of Marine Mammalogy 2017
Last updated: November 2018
To understand the diet of a cetacean species, researchers can collect a sample of its feces or analyze the stomach contents of a carcass. These two techniques have their limitations however, only revealing what the whale has ingested during its last few few meals. Two techniques are used to obtain a better idea of what whales eat: nitrogen (N) and carbon (C) stable isotope analysis and analysis of the fatty acids contained in whale baleen and other tissues.
Witnesses to question
When a whale is stranded on the shores of the St. Lawrence, the team of Véronique Lesage (Fisheries and Oceans Canada) travels to the scene to collect important “witnesses” that will subsequently be “questioned” in the lab: baleen and skin, fat, and muscle samples. Further, skin and fat samples can be obtained from living animals as part of a large rorqual biopsy program. These “witnesses” will reveal the diet of the rorquals and its evolution over time.
This analysis consists of measuring the abundance of stable isotopes 13C and 15N compared to the more common forms of these elements, 12C and 14N. These “signatures” allow to glean information on the type of prey ingested (e.g. plankton or fish) and on the region where the animal has fed (e.g. Estuary or Gulf). The measurements obtained in the skin and muscle samples are a reflection of what the whale has eaten in the previous two months. As for the baleen, it is a veritable archive of the 10-15 years preceding the animal’s death: the farther we move away from the gum, the farther back we go in time!
A great diversity of fatty acid chains exists in marine ecosystems. Each animal species has a fatty acid signature that is unique and that depends on its diet. By comparing the fatty acids found in a whale’s blubber layer with those found in its potential prey, we can determine the species that it has consumed.
Genetic secrets, accumulated pollutants and even diet are examples of data that can be collected thanks to a tiny piece of skin and fat. All that’s needed is a crossbow armed with a dart-tipped bolt (arrow). In this manner a few milligrams of skin and fat are sampled without immobilizing the whale and without disturbing it for more than a few seconds. In the St. Lawrence, MICS has been using this technique since 1990 to determine the sex of humpback, blue, fin and minke whales. The GREMM has been conducting biopsies on belugas since 1994 to identify their sex and family links and since 1998 on fin whales to determine notably where these giants are from
Does it hurt?
Before they began to be performed, beluga biopsies underwent careful scrutiny by the GREMM. After all, we’re talking about collecting a small piece of skin and fat from a living animal belonging to a threatened population. After weighing the pros and cons, the GREMM decided in 1994 to go forward while closely monitoring the potential risks of this type of intervention. During her master’s program at McGill University and under the GREMM’s supervision, Véronik de la Chenelière conducted a detailed analysis of the risks and benefits of this technique based on three years of data. In her thesis, she proposes a process to facilitate decision-making for research projects conducted on protected populations. This process, rather general in nature, can help researchers in their studies of protected populations. She concluded that biopsies represent few risks for St. Lawrence belugas, but rather that they can provide significant benefits to this population since the project is designed to protect this species.
0:00 – Aboard the Bleuvet, the GREMM crew sets out to conduct beluga research.
0:07 – Photo-identification and data collection.
0:26 – One of the belugas is biopsied.
0:37 – Cutting of skin and fat sample.
Progesterone is a steroid hormone secreted by the ovary in female mammals. By analyzing the blood, saliva, eye secretions, feces or subcutaneous blubber layer in females of certain cetacean species (killer whale, minke whale, fin whale), it has been demonstrated that it is possible to determine their stage of maturity or period of reproductive cycle. Researchers can thus identify the age at which females reach sexual maturity or even conduct pregnancy tests on them! Questions of this nature can help biologists better understand the health of populations. The advantage of this method is that it only requires a small sample that can be collected relatively easily from living animals in their natural environment. Some researchers have even been able to measure progesterone from whale spouts! It is a relatively new and highly promising technique.
Whale breath contains answers to many mysteries. It often contains dead cells that have information about DNA as well as hormones, lipids, proteins, and microbes from the whale’s respiratory tract. This provides scientists the ability to not only diagnose sick whales, but also keep a record of what a normal tract looks like for a healthy individual. Breath sampling can also be used on certain species to detect pregnancy.
There are two main ways to collect a breath sample:
- Using a pole: In this conventional method, a Petri dish is attached to a long pole that a person holds above an exhaling whale from a vessel. Before approaching a whale, the research team collects data on the animal and records its breathing sequence to better predict its surface intervals. Though it is a good way to gather a sample, this method requires the vessel to be in rather close proximity to the whale, thereby resulting in a possible increase in stress hormones.
- Using a small UAS (Unmanned Aerial Systems):
For whales that have a prominent blow, the answer to the above problem is a UAS. It is a comparatively less invasive method and consists of a UAV (Unmanned Aerial Vehicle)—often referred to as a drone—a payload (often a camera or anything else attached) and a ground station. With the advancement of aerial technology and its user-friendliness, the market is filled with UAVs of all shapes and sizes. However, a UAS designed to collect breath samples from an ocean giant cannot be just any UAS; it has to be waterproof and have the ability to withstand the massive upward thrust that accompanies a whale’s blow. Additionally, using a UAS at sea is not necessarily an easy job. It takes skill, accuracy and precision, especially when working with marine mammals. Not only that, taking off and landing from a moving platform (a boat, in this case) requires training and coordination between team members.
Video: A UAS with a Petri dish can also be flown towards the whale’s blow to collect a sample in a less invasive manner. Researchers from Woods Hole Oceanographic Institute (WHOI), NOAA Fisheries Southwest Science Center, SR2 Sealife, and the Vancouver Aquarium analyzed the samples collected using the UAS in this video to identify a core group of bacteria found in respiratory tracts of healthy whales. © WHOI
Skilled UAV operators work in a team of at least two people: a Pilot-in-Charge (PIC) and an observer. For at-sea operations, the observer also often has the responsibility to launch the UAV and help with its retrieval.
To collect a breath sample, the UAS is equipped with a Petri dish attached either on the top or the front. Before approaching a whale, the research team collects data on the animal and records its breathing sequence to better predict its surface intervals. When everything is set up and ready to go, the UAS is flown over the water and towards the surfacing whale to obtain a sample of the blow.
After samples are collected using either of the methods, they are stored at -80 degree Celsius to ensure they stay usable for analyses.
Note: Special permits are required to fly a UAS in close proximity to marine mammals for research.
Last updated: November 2018
Counting whales is no easy task! To do so, scientists conduct aerial surveys. From high in the air, whales are clearly visible when they surface to breath. They only remain there for a very brief moment, however, as they spend between 40 and 80% of their lives below the surface.
- A portion of a whale-inhabited sector is flown over while following a specific itinerary (systematic or random, depending on the method selected), preferably on a calm day with excellent visibility.
- Such surveys may consist of visual surveys, photo surveys, or a combination of the two. During visual surveys, the presence of whales is noted by observers. In photo surveys a camera takes pictures at regular intervals. Back at the lab, the whales visible in the photos are counted.
- To reach an estimate, the number of whales counted in the photos must first be adjusted to account for sectors not covered.
- Subsequently, a correction must be made to take into consideration animals that were below the surface and thus invisible to the camera and to observers when the plane was passing overhead.
Last update: May 2017
Every whale is unique. Observe the natural marks such as the pigmentation, colouration and the shape of the dorsal fin. Notice also the presence of deformities or scars.
Photo-identification has been used since the 1930s on a number of species including elephants, gorillas, seals, giraffes and leopards. It is used today by researchers in the St. Lawrence to study belugas, fin whales, blue whales, humpback whales, minke whales, sperm whales and North Atlantic right whales. It facilitates the monitoring of the movements, social organization and behaviour of whales as well as estimating their abundance.
Every hour spent at sea with whales translates into several of hours of work in the lab. Photos are carefully analyzed, compared to those of several individuals and finally matched according to a series of rigorous criteria. With time, the technique has evolved: rolls of black-and-white film have been abandoned in favour of the digital photos used today. Such photos, reworked or processed by computer, are far quicker to reveal the identities of the giants!
To date, no computer program has been able to provide results of comparable accuracy as human visual recognition of photos. Such work demands a great deal of time and patience! To discover the nuts and bolts of beluga pairing, read these two articles: With the Belugas: The Fascinating Work Behind Beluga Pairing and Part II.
Unless one measures a beached specimen, it is almost impossible to take measurements of a whale manually. However, biologists need this information – length, width, height, circumference, mass, etc. – to get an idea of the animal’s state of health.
Taking accurate morphological measurements of cetaceans presents several challenges: the animals are immersed in water, seldom sit still and their bodies, far from being flat like a pancake, are full of curves. Researchers have therefore developed a number of methods to achieve this: some, such as photogrammetry, are used in the presence of the animal, while others can be applied remotely, such as measuring the size of elephant dung to determine the animal’s mass.
Converting photos to measurements
n the 19th century, Aimé Laussedat, a French colonel and geometry professor, discovered that it is possible to measure distances using photographs of landscapes. The measurements of an object or an animal can be calculated from photographs when the ratio of the focal length of the lens and the distance between the camera and the object are known. This method is still used today, for example to measure sperm whales at the surface. Researchers must combine Laussedat’s method with a rangefinder to determine the distance between the camera and the object.
Biologists also use parallel lasers to directly obtain a measurement scale. Thanks to the lasers, the measurement is projected onto the animal. This way, one does not need a rangefinder or complex analyses. This method is used on cetaceans when they come to the surface.
In recent years, photogrammetry has been combined with a high-resolution camera installed on a drone to capture images of whales without intruding into their daily lives. Drones are relatively quiet and stable in flight, which allows them to fly close to the water without disturbing the whales. This non-intrusive approach eliminates the need for sedatives to immobilize the animals, handle them, or to lug bulky equipment into the field.
Are photos reliable?
To describe marine mammals, biologists combine photogrammetric data with morphological models. Mathematically, they transform the animal into a series of truncated cones to estimate the dimensions of the animal.
The next step is to make sure the models are reliable: are the results representative of reality? This is done by calculating the discrepancy between the mathematical model data and flesh-and-bone data (either from captive animals or stranded carcasses). If the difference is minor, the measurements obtained by photogrammetry can be considered to be as effective as a measuring tape or a scale!
For more on this subject
How Do We Measure the Length of a Whale? (Baleines en direct, 01/11/2017)
With the belugas… And Their Waist Measurements! (Baleines en direct, 27/07/2018)
Last update: August 2018
When a whale dies, its carcass is often carried by the currents and tides and can wash up on the beach. Scientists study these carcasses in order to know the pollutants and diseases that pose a threat to the health of the whales. Along the St. Lawrence, report beached marine mammals to the Quebec Marine Mammals Emergencies Network at 1-877-7baleine (1-877-722-5346). If it is a marine mammal, a team will be mobilized to the location to assess the state of the carcass and take measurements and samples.
If it is a beluga and the carcass is fresh, it will be transported by truck to the Université de Montréal’s faculty of veterinary medicine in Saint-Hyacinthe. A detailed necropsy and chemical analyses will do wonders to shed light on the causes of the animal’s death and its exposure to pollution.
Whales only spend 10-20% of their time at the water’s surface. This is often all scientists have to study them. In the St. Lawrence, scientists use satellite and radio telemetry. These techniques allow to study whales in their underwater world.
Ideal for understanding the details of a whale’s life and monitoring its movements over short distances.
Janie Giard and Robert Michaud, of the GREMM and Véronique Lesage, of the Maurice Lamontagne Institute (Fisheries and Oceans Canada), study several rorqual species using data recorders equipped with radio transmitters. Some transmitters, such as those developed by researchers at the Woods Hole Oceanographic Institution for a beluga project in collaboration with the GREMM, are fitted with a sound-recording device. Such transmitters are used to study the vocalization behaviour of belugas and their exposure to ambient noise.
Two techniques are used to attach tags to the backs of whales: poles and crossbows
0:00 – 0:00 – Aboard the Bleuvet: Michel Moisan and Renaud Pintiaux of the GREMM, and Véronique Lesage of Fisheries and Oceans Canada. The team finds humpback whales Tic Tac Toe and Aramis.
0:06 – 0:06 – Approaching the two whales.
0:15 – Pole-assisted placement of tag onto the back of Tic Tac Toe: it’s a success! Aramis is nearby.
0:39 – Aramis is spotted first, then Tic Tac Toe, with the yellow and orange tag on its back. The signal is heard as picked up by the receiver.
0:54 – Throughout the monitoring, the crew collects data whenever the whale surfaces. Here, Véronique Lesage.
1:00 – The Parks Canada team, on board L’Alliance, conducts a prey census by means of acoustic monitoring, in the sector frequented by Tic Tac Toe.
1:05 – The tag falls off Tic Tac Toe’s back during a breach. Shortly thereafter, she is observed flipper slapping. The tag was recovered.
Satellite telemetry is ideal for studying the movements of a whale over long distances and to obtain information synopses on its activities over extended periods. However, this technique implies a number of challenges:
- Placing transmitters on animals in the wild which only surface briefly and which are often difficult to approach;
- High costs of this type of tag and subscription to a satellite communication system;
- Development of prototypes that do not cause injury to the whales;
- And the risks and uncertainties associated with attaching a tag to a smooth and hydrodynamic body moving through the water at high speeds and interacting with other organisms and obstacles!
Since 2009, a team composed of researchers from Fisheries and Oceans Canada, MICS and the Alaska Sealife Center has been using telemetry on blue whales in the St. Lawrence to document, from spring to fall, the animals’ movements, their utilization of known sectors and to discover new ones, including wintering grounds.