Seeing a whale or dolphin leap out of the water and crash down with an almighty splash is undoubtedly one of the most spectacular sights at sea. The scientific definition for such an aerial display is a ‘breach’, an intentional jump from the water in which at least 40% of the animal’s body emerges.
Of all the cetaceans, humpback, right and sperm whales, and offshore dolphins, are the most frequent breachers. Each have slightly different styles of approach to the surface and aerial acrobatics. Sperm whales and dolphins approach the surface vertically from depth, whilst humpbacks and right whales make a shallower horizontal approach to gain speed until the final seconds in which they raise their heads and flukes, twisting using their flippers to launch themselves into the air. Considering a humpback whale can reach a weight of 40 tonnes, this energetic display is seriously impressive. Above the surface, breaching form is also varied. For large whales, the animal classically twirls to land on its back or side, revealing around 90% of its body at peak emergence. More rarely big whales may belly flop, of course with an enormous accompanying splash. Smaller cetacean species, or whale calves, can completely clear the water in a breach. Young spotted dolphins have been recorded to leap an astounding 15 feet into the air – higher than a double decker bus! Breaches are also often performed in series, one after the other. One humpback whale in the West Indies was seen to breach 130 times in a 75-minute period, which would use up a LOT of energy.
So why do cetaceans breach? Despite it being a common activity performed by many whales and dolphins, scientists still don’t really know why. Lots of plausible theories have been proposed. Several, or all, of these hypotheses could be true, depending on the environmental and social context, and cetacean species in question. So, let’s explore a few of these explanations.
Figure 1: Humpback whale breaching. (Credit: M. Somerville).
Communication
Breaching behaviour seems to be strongly correlated with sociality. Breaching rates tend to be higher for the more social species, and when group sizes are larger. For the more solitary species, such as blue and Bryde’s whales, breaching occurs only rarely. Why is this?
In socially structured groups, communication is extremely important for co-ordinating group activities, fission and fusion. In spinner dolphins and humpback whales, breaching occurs most during changes of group activity or composition, such as initiation of a feeding bout. For example, spinner dolphins increase aerial behaviours during the transition from the resting period to the foraging period in their 24-hour cycle; when individuals are widely dispersed; or when visibility is low at night. During migration, cetaceans seldom feed, yet aerial behaviours are often observed despite using up lots of energy. It has thus been suggested that breaching may mediate social interactions by maintaining contact between groups.
The sound of a body slamming to the surface after a leap will propagate only short distances compared to cetacean vocalizations in water. Thus, the acoustics of a breach will only transmit information to individuals close-by, avoiding unwanted signalling to prey, predators or conspecifics. These signals probably transfer information on motivation or intent.
Neighbouring animals are unlikely to be able to see the breachers body above the surface, so it is the sound produced from hitting the surface that must transmit information. It is proposed that breaching is part of an ‘honest signalling system’, in which important information about the signaller is transmitted to receivers. The sound, and under-water bubble pattern, produced by a breach reliably indicates the physical abilities of the breaching individual, such as strength and agility. The larger the splash, the bigger the individual and the faster it has propelled itself out of the water. During a breach, a humpback whale uses about 1% of its daily energy expenditure. If breaches are performed in sequence, this is a significant utilisation of energy. This signals to others that the individual can afford ‘wasting’ energy on jumping out of the water, showing off its physical fitness.
During the humpback whale breeding season, breaching activity is more frequently observed. Male groups competing for a female breach regularly, supposedly displaying their physical strength and endurance. So, breaches can be used to assert dominance over others, or attract mates during courtship.
A breach may also add emphasis or draw attention to some other signal, such as a vocalization or visual display, sort of like a ‘physical exclamation mark’.
Figure 2: Bottlenose dolphin breaching. (Credit: B. Brederlau).
Play
‘Play’ is a blurry concept, and is often attributed to any behaviour without an obvious biological function. Breaching is common in social situations and among young cetaceans – characteristics of playful behaviour. It is usually calves and juveniles that leap the highest, and in right, gray, and humpback whales, animals will breach when only a few weeks old. Perhaps this acrobatic activity helps the development of musculature, body awareness, and co-ordination. Yet this doesn’t really satisfactorily explain why adult whales breach too.
Cleansing
For a cetacean, little creatures such as barnacles, remoras, lice, that hitch-hike attached to their bodies can be quite annoying. These ectoparasites not only increase the drag force and the energy costs of movement, but are also itchy. One humpback whale was found with 454kg of barnacles attached to its body, just imagine lugging all that extra weight around! Breaching can act to dislodge or loosen these critters, helping to remove them. For example, 44% of Hawaiian spinner dolphins that breached had remoras (small fish that latch on via disk-like suckers) attached, suggesting that breaching may be an attempt to shake off the extra passengers. But this still doesn’t explain why the other 66% of spinner dolphins were breaching ….
Figure 3. Barnacles on the head of a gray whale. (Credit: L. Handley).
Feeding
A hefty cetacean body slamming the water would be enough to scare anyone. One hypothesis is that breaching is used to stun, scare, or herd prey, such as schools of fish. Lobtailing (tail slapping) is often used for this purpose and is sometimes associated with breaching. This may explain some breaches, but not those observed in non-feeding circumstances.
A bit of everything
It seems that there is no single all-scenarios-covered explanation for why cetaceans breach. In general, breaching seems to be associated with social situations, indicating an important role in communication. Depending on the social and environmental context, leaping out of the water can have different functions. Identifying which function a breach serves is challenging to say the least, with solid explanations still evading marine scientists.
Written by Liz Heard, Volunteer 2017.
