Filipa Cunha Oliveira - Variation in heart rate according to dive depth in captive common bottlenose dolphins

Who am I?

As a Linköping University student enrolled in the Master of Applied Ethology and Animal Biology, I had the opportunity to collect data to write my thesis in Spain, in the biggest Aquarium in Europe. Before coming to study at LiU, I graduated in Aquatic Sciences, therefore I always wanted to ensure that I would keep in contact with marine life no matter the master’s program I chose. When the opportunity appeared, it was with extreme happiness that I embraced the project. Although the master’s focus is on animal behavior, each student could select the master project that is best suited to them, therefore I decided to do mine in animal physiology. 

My master project – Variation in heart rate according to dive depth in captive common bottlenose dolphins 

Marine mammals spend much of their time underwater, facing varying hydrostatic pressures while holding their breath. To cope with these conditions, their primary

physiological response to diving is a reduction in heart rate (fH) below resting levels, coupled with extensive peripheral vasoconstriction. These adaptations help extend dive duration by conserving oxygen, prioritizing its supply to vital organs like the heart and brain, and reducing the blood flow to organs that can function with reduced oxygen supply. Measuring fH can be accomplished using a single suction cup tag (Fig. 1A) that is attached to the dolphin’s body to record the heart's electrical activity (Fig. 2), resulting in an electrocardiogram (ECG). After identifying the R waves, which represent the depolarization of the ventricles, fH is calculated from the interval between these waves (Fig. 1B).

Among and within dives, fH can vary due to several factors, such as dive duration and depth, the purpose of the dive, locomotor activity, changes in dive expectations, stressors, and others. It is well established that the fH decreases with the duration of the dive, however, since deeper dives are usually longer, it is difficult to evaluate if this variation in fH is only due to dive duration, dive depth, or both. Therefore, my master thesis project aims to assess the confounding effect of dive duration and investigate if there is any variation in fH according to dive depth in bottlenose dolphins held in human care. This will be accomplished by maintaining the same dolphins’ dive duration and only varying the depth of the dives while recording their fH at each depth.

In order to collect my data, bottlenose dolphins (Tursiops truncatus) housed at Oceanogràfic Valencia, Spain, undergo training to hold their breath during three distinct dive categories (approximately 0,5 m, 5 m, and 10 m), where we measure their fH using electrocardiography. The trials for the project employ operant conditioning, using positive reinforcement, ensuring the dolphins’ participation is voluntary and that they can withdraw at any point. 

Physiology plays a crucial role in determining a species' diving capacity and foraging strategies, which are increasingly impacted by changes in prey availability and distribution due to overfishing, pollution, and climate change. In this context, monitoring how fH adjusts during dives at different depths provides valuable insights into how bottlenose dolphins – and potentially other marine mammals – adapt to the specific physiological demands of diving in a changing environment. 

 

My experience at the Oceanographic

Valencia Oceanographic goes far beyond its captivating exhibits, playing a key role in research, conservation, and education initiatives. Working here, particularly with the aquarium's main attraction – the dolphins – comes with its unique challenges. The trainers are crucial in incorporating this project into the dolphins' daily routines. Therefore, with their expertise and the support of my supervisor, Andreas Fahlman, I aim for this research to advance our understanding of these remarkable species and help address significant gaps in our knowledge.