An Amazing Behavior
Cetaceans—whales, dolphins, and porpoises—comprise a group of mammals that demonstrate some of the most extreme adaptations of the mammal world. These creatures possess a range of intricate and specialized adaptations to deal with the myriad physiological issues that a warm-blooded, air-breathing animal must deal with in the course of trying to make a living in the ocean.
Air Management Tactics
Breathing is a basic survival function, but for cetaceans, it is actually under voluntary control—unlike with terrestrial mammals, as anyone who has ever tried to test their breath-holding limits has surely experienced. Not only can these marine mammals control their breathing precisely, but it also appears that some species have taken air-management tactics to new and creative heights.
Dolphins naturally expel air bubbles as they exhale below the surface of the ocean, and multiple aquariums and oceanariums have documented incidents of dolphins using exhaled air to form bubbles, rings, or torus formations, which they can spin, split, merge and otherwise “play” with, either alone or in groups. These behaviors are incredible to observe, as the dolphins essentially manufacture and play with their own toys in the water. The production and manipulation of these structures is achieved entirely through dolphins controlling the release of their breath, and subsequently moving their bodies to create specific vortical conditions around the expelled air bubbles. A paper by McGowan et al. (1997) reported observations of dolphins producing a variety of bubble formations, and then interacting with them: biting their creations, swiping at them with flippers or flukes, swimming through them, catching and linking multiple rings, and maneuvering bubbles/rings around without destroying the delicate structures.
The McGowan study, which was conducted at Six Flags Marine World in California, also suggested that dolphins seem to plan the execution of ring formation, positioning themselves just right in the water column before forming a ring. In addition, the dolphins appeared to monitor the quality of their rings. The practice of evaluation is a critical skill, as it is necessary to have a solid single ring in order to produce the even more intricate double ring formations. These demonstrations of planning and assessment of performance are fascinating demonstrations of the cognitive capabilities of these animals, which have an encephalization quotient (EQ)—an estimation of intelligence based on the size of the brain in relation to total body size—surpassing those of many other mammals, including chimpanzees, gorillas, and orangutans. Of course, there is an ongoing debate regarding the accuracy of EQ as a measure of overall intelligence, as well as how to define intelligence across species with dramatically different lifestyles. Despite that controversy, all evidence points to the fact that dolphins have extremely impressive cognitive abilities.
We can see that the dolphin bubble rings and bubbles are used to entertain themselves (and others) in captivity, but that raises an obvious question: do wild dolphins do this, and what could the practical utility of ring-tricks possibly be?
Eco-Friendly Fishing Techniques
Wild dolphins do, in fact, use bubble formations, but in a much more serious context—hunting. A report by Fertl and Würsig (1995), of Texas A&M’s Marine Mammal Research Program, describes observations of a group of adult and juvenile dolphins working cooperatively to corral a school of fish with their bubble formations. The dolphins swam underneath the fish while expelling bubbles, forcing the fish upwards in the water column. Fertl and Würsig suggest that the bubbles serve two purposes:
- to knock fish off course and isolate them from the school, making them easier targets, and
- to create an undertow in the water, which essentially creates a vortex that the fish “fall” into, hindering their escape.
Some of the dolphins continued to work at containing the fish with bubbles, while other members of the group took turns capturing individual fish.
The execution of such an operation can be a beautifully coordinated team effort, but it appears that individual dolphins find ways to use bubbles to catch fish when they are working solo. Fertl and Wilson also observed a lone male bottlenose dolphin using bubble bursts to manipulate a small school of fish, possibly explaining why bubble bursts have periodically been sighted near bottlenose dolphins, as they feed.
Specialized Sonar Systems
Some aspects of cetaceans’ manufacture and use of bubbles and bubble rings remain enigmatic. For example, bubble bursts and formations should, in theory, disrupt sonar/echolocation transmission. As cetaceans use echolocation to “see” underwater, this disruption would essentially blind the animals to what is going on behind the bubbles that they emit—presumably obscuring their perception of the prey that they are pursuing.
This issue has fascinated engineers, as the answer to the question of how dolphins “see” through their bubbles could have profound implications for improving the effectiveness of sonar technology in turbid conditions. Researchers at the University of Southampton used the dolphin bubble mystery as a springboard that led to a new technology, called Twin Inverted Pulse Sonar. This method uses dual pulses of sound as a way to effectively use sonar in bubbly conditions, without having the “picture” scattered. Although there is still uncertainty over how exactly dolphins have solved the problem (engineers independently developed the concept of the twin-inverted pulses, it was not discovered in dolphins), interest in their activities has yielded a significant new industrial advancement. Dolphin bubble nets have joined a plethora of other cases in which nature has inspired new human technologies.
Several wild cetaceans—including humpback whales, orcas and Atlantic spotted and bottlenose dolphins—have been observed producing bubble formations. The phenomenon is well documented in captivity, and there have been verified observations of the behavior in the wild. Much more research is needed, however, before we can fully understand the mechanics and strategies involved in the development of this amazing skill in multiple marine mammal species.
Check out more dolphin bubbles at the following links: