The main goal of our Greenland shark research mission was to gather physiological and biological information about the sharks. We tagged every shark we caught with an identification tag, in case they were caught in the future. We measured body and fin length in all sharks and took a small sample of tissue from each animal for DNA analysis. To further our understanding of how these sharks use their environment, we tagged some with satellite bio-loggers, which track their location as they move about in the depths. We also wanted to understand more about the way they swim – as Greenland sharks are considered among the slowest swimmers in the sea. We employed a different kind of tag for this called an accelerometry tag.
Some of the sharks were injured on the line – either by being bitten by other Greenland sharks or by swallowing hooks. These sharks were humanely euthanized and brought aboard the vessel so that we could study their internal anatomy. We studied the reproductive organs of both male and female sharks. We also studied their skeletal muscle to link how the muscles contract with their slow swimming speed. Lastly, we wanted to study their hearts and blood circulation. We wanted to learn about heart rate, about blood pressure about how the heart muscle contracts and how much blood it pumps, and about blood chemistry.
John Fleng Steffensen, University of Copenhagen
The Greenland Shark first caught my attention back in 2001 when the captain of our research vessel told me he’d heard that the creatures live to be very old. When I searched for past research on this creature, I only found one reference to their age, from back in the 1960s, when P.M. Hansen found that one shark had grown only 8 cm in 16 years. Such slow growth seemed to suggest they might live very long. It was our work in finding a way to calculate the age of these sharks that eventually determined that they could indeed live for centuries! Our cruises to southwestern Greenland have taught us much more than just the sharks’ longevity: on our latest mission, we looked at heart muscles, properties of the circulatory system (heart rate and blood pressure), where and how fast they swim, and filming their feeding at depths of 200 to 600 meters.
Takuji Noda, The Institute of Statistical Mathematics
I am an interdisciplinary scientist working between biology and informatics. My main interests are locomotion, behaviour and physiology of fish in their natural environment and how to measure that information in various types and sizes of fish. Therefore, I am developing customized animal-attached data loggers, composed of a variety of sensors (the technique is called bio-logging). With colleagues, I have established a company called Biologging Solutions Inc. to support the creation of customized data loggers and solutions for improving data recovery.
I am interested in the swimming ability and behaviour of Greenland sharks, which live in deep and cold waters. In the fjord of Greenland during the expedition, we attached multiple-sensor data loggers to Greenland sharks. The loggers automatically detached from the sharks and popped up to the surface of the water, where we could find and recover them using radio telemetry. Using a high-resolution accelerometer and speedometer, we measured swimming patterns such as tail-beat frequency and speed to understand how slowly they move and if they exhibit bursting movement when feeding.
Although it was difficult to measure bursting moment during the recording period, the data showed the sharks generally swims at very slow tail-beat frequency (at about 6 seconds per beat). This supports the measurements from physiological experiments in the lab.
Julius Nielsen, University of Copenhagen
I am a PhD student from the University of Copenhagen and have been working on the #GreenlandSharkProject since 2012. This project investigates many aspects of the biology of Greenland sharks including longevity, feeding ecology, migration patterns and population genetics.
I first started studying sharks caught as bycatch by the Greenland Institute of Natural Resources during fish monitoring surveys. These sharks gave unique insights into this poorly studied species, for example revealing their extreme longevity. The oldest shark we analysed was at least 272 years old, making the Greenland shark the longest-living vertebrate known. We also learned that they catch fast-swimming prey like Atlantic cod and seals, an unexpected finding given their seemingly sluggish nature. How they do this is still a mystery; I expect they might be ambush predators, who catch prey by being stealthy rather than speedy, as well as opportunistic feeders, scavenging carcasses from the ocean floor.
On this expedition, my main focus is to deploy satellite tags on the sharks to learn more about their movement patterns. We especially want to tag sexually mature animals to learn about mating areas and pupping grounds. I will also take samples from any sharks too injured to release, to inform my ongoing investigations about feeding, longevity, and reproductive biology.
Diego Bernal, University of Massachusetts Dartmouth
I’m a comparative physiologist who studies how temperature affects the swimming muscles of fish who are elite swimmers. These quick fish, such as the tuna and mako shark, keep their bodies warm. The Greenland shark is the opposite of the fish I usually study, it’s slow and cold. I was curious to learn how its muscles function in its cold environment and how it manages to catch its prey. On our last expedition to study these sharks, the equipment we brought to study the muscles was too small for the huge muscle fibres. We also learned that we needed a way to keep the samples at 1-2 degrees Celsius, to mimic the water temperature where the sharks live.
Peter G Bushnell, Indiana University South Bend
I am a comparative physiologist: I’m interested in how different animals adapt their bodily functions to meet their needs. I focus on the circulatory and respiratory systems of marine animals, and have been studying polar animals in the Arctic and Antarctic for more than 25 years. When my colleague John Steffensen and I discovered how little was known about Greenland sharks, we decided to look at various aspects of their biology such as their swimming ability, migratory movements, diet, metabolism, and reproduction.
On this particular trip I was interested in how their hearts work, as this will impact their cardiovascular system, metabolism, and swimming ability. To do that, I cut out little strips of heart muscle and stretched them between clips. Every time a strip was stimulated by a small electric current, as happens in a normal heart to cause it to beat, the strip would briefly contract (shorten) and then relax: this is called a twitch. By measuring various aspects of the twitch, like strength and duration, we can learn a lot about how the heart might operate in an intact animal.
Making this technique work in Greenland sharks proved very challenging. However, I have managed to conclude that a twitch takes about 3-5 seconds, putting maximum heart rate somewhere between 12-20 beats/min. To put that in perspective, your normal resting heart rate is about 60-70 beats a minute with a maximum heart rate around 180 beats/min. Heart function is temperature sensitive, so it is not surprising that Greenland sharks swimming in very cold and deep water have much lower heart rates. However, I believe their heart contracts very slowly, which is in keeping with the idea that they don’t do anything quickly.
Robert Shadwick, University of British Columbia
I am a physiologist who studies animal form and function, also known as biomechanics. I am interested in the structure and mechanics of the heart and blood vessels in a variety of animals. Blood pressure is an important indicator in an animal. In fish, it reflects the level of activity of a species. Tuna for example are fast, continuous swimmers and have relatively high blood pressure compared to slower fish such as carps.
Activity levels vary greatly among shark species. The Greenland shark is generally considered very sluggish, but may swim fast to capture and eat seals. The purpose of my study was to estimate average blood pressure in the Greenland shark, to understand how these large sharks compare to other species.
To do this, we used the aorta, a large blood vessel that carries blood to the gills. The aorta is very elastic at low blood pressure, but when blood pressure is high the aorta wall becomes stiff. This transition between elastic and stiff typically occurs around the average blood pressure of the animal. By measuring the flexibility of Greenland shark aortas at different pressures, we can estimate the average blood pressure of these animals.
Our preliminary results show that the Greenland shark aorta is very flexible at pressures below 3 kilopascals (kPa, a measurement of pressure), but becomes very stiff with further increase in pressure. Therefore, we can tentatively estimate the average blood pressure to be around 2-3kPa. Our own blood pressure, in comparison, is about five times more (13 kPa), and the slow-moving dogfish shark’s is 4kPa. These results support the idea that Greenland sharks are indeed a sluggish and likely a slow-moving species.
Holly Shiels, University of Manchester
As a fish cardiovascular scientist I am interested in the mechanisms that maintain or adjust heart function in a changing environment. Such knowledge has application to cardiac health and disease and in predicting how organisms, populations, ecosystems and natural resources respond to environmental change and stressors.
Investigating cardiovascular function in the Greenland shark is very exciting, because these animals are long-lived and thrive in cold environments. Several of their cardiac features make them particularly interesting. The first is their very slow heartbeat. Although not surprising for an animal living at 1-2⁰C, it takes a long time for their hearts to fill with blood between one beat and the next. This affects how much the heart stretches out and how strongly it then contracts to push out the blood. We suspect stretch regulation of force is particularly important in this shark.
We are also interested in the Greenland shark’s longevity. In humans, age is associated with many cardiovascular problems, such as fibrosis (the aged heart becoming stiffer). A key question for us is whether the Greenland shark heart stiffens with age. And if it does, how does that affect its ability to fill will large blood volumes between heart beats?
Both stretch and fibrosis of the heart muscle create an environment for arrhythmia – irregular heart-beats. Arrhythmias are dangerous in humans, but what about sharks?
During the expedition, we used echocardiography to measure heart rate before releasing the sharks. In animals too injured to release, we collected the hearts and measured pressure and flow relationships. We then preserved the hearts to study their structure, including fibrosis, in the lab.
Emil Aputsiaq Flindt Christensen, University of Copenhagen
I am a biologist with special interest in the interaction between ecology and physiology, the so-called ecophysiology, of fishes. I work both in the field, fitting animals with tags to study their behavior in the wild, and in the lab studying physiology through both animal behavior and biochemical analyses of tissues.
My research has focused a lot on the salt and water balance in fish. In that regard, sharks and similar species are “osmo-conformers”, meaning that they maintain water balance by producing organic molecules such as urea and a chemical called TMAO.
TMAO is an especially interesting compound to me, because it stabilizes chemical reactions that happen in the body, which is helpful under the high pressure conditions found in the deep sea. Thus, analyzing TMAO levels in the Greenland shark might tell us something about how deep it swims.
On a side note, Greenlandic hunters feed their dogs with Greenland shark, but sometimes the dogs get poisoned. This might be because TMAO degrades to a poisonous compound called TMA.
Follow #SharkDiary on Twitter to see all the updates about the expedition.
This expedition was made possible by funding from the Danish Centre for Marine Research, the Greenland Institute of Natural Resources, The Danish Natural Science Research Council and the Carlsberg Foundation.