Rachel Cartwright teaches biology at California State University Channel Islands and is studying trends in habitat use in humpback whale mother-calf pairs in Hawaiian waters.
Friday, March 15
Within the world of whales, blue whales may be the largest and killer whales are probably the most charismatic. But when it comes to acrobatics, humpback whales lead the way.
There?s just no sight quite like a breaching humpback whale. This 40-ton whale leaps high out of the water, makes a midair roll through 180 degrees and then lands with a huge, thumping splash. It may not always be graceful, but it?s certainly impressive.
Breaching is fairly rare in feeding areas, but on the breeding grounds it?s quite common. Single whales breach, pairs breach together, and sometimes a mother, her calf and their escort will breach in an explosive sequence of leaping whales and white water.
You?d probably expect that we whale researchers would have a good explanation for such eye-catching behavior. The truth is, we don?t know why whales breach.
At least for adults, we would suspect some sort of social context or useful benefit for such a large, showy and energetic behavior. An early suggestion was that whales breach to dislodge the heavy load of barnacles that they attract while in their cool temperate feeding regions, but we now know that this is not the case; in fact, barnacles are part of the whale?s armor, used by males in dominance disputes and also perhaps as part of the defense against predators.
There have been some suggestions that breaches are some form of acoustic signal, used more frequently on windy days when surface chop drowns out more subtle sounds. But even on the very calmest days, breaching can be a frequent behavior, often coming in waves that really tempt the speculation that this is all prearranged and singularly designed to entertain researchers and whale-watchers alike.
Today is one of those days; calm, glassy waters stretch across the channel as we head out. We spot a whale breaching intermittently in the distance, and then another whale breaches close by. We select our group for the day: a mother, calf and ever-hopeful escort. We plan to conduct a focal follow, where we mirror the whales? movements in the research vessel, looking to see where and when the three rest and where they travel.
But in just a few minutes our cameras hit the decks. The escort of our focal group roars from the water beside us. The whale propels upward like a submarine surfacing from the depths, water pouring from it. We smell a bright, fishy, Alaskan aroma and then collectively whoop as the whale splashes back down in a cacophony of white water. It?s like watching fireworks.
In the past, we?ve been in the water and watched whales breach from underwater. For adults, it?s a surprisingly effortless behavior. Two good, deep flexes of the caudal muscles and the flukes propel the whale up and out of the water. When whales breach close by, it?s surprisingly quiet in the water, but the breach does produce a huge mass of bubbles, and if you?re too close to that ? well, it?s something like being briefly immersed in a washing machine on the spin cycle.
Specifically, our work focuses on calf behavior and development, and in calves breaching is frequent and often repetitive, with sequences of 10, 15 and even 20 breaches continuing over a period of travel.
All this high-energy behavior seems at odds with the otherwise energetically conservative behavior adopted by new mothers. However, as our studies progress, a possible purpose for repetitive breaching may be emerging.
One of the key adaptive traits in whales, and indeed in all marine mammals, is their ability to hold the breath and make extended dives. This facilitates foraging and reduces the costs of travel, and in many marine mammals it minimizes predation risk too.
Marine mammals employ a range of mechanisms to increase their breath-holding capacity, from decreased heart rates to redistribution of oxygenated blood supplies to key regions.
Additionally, a ubiquitous adaptive mechanism at the cellular level is the presence of myoglobin. Myoglobin is an oxygen carrier, so cells with increased amounts of myoglobin can stockpile supplies of oxygen. This maintains aerobic respiration and extends breath-holding times.
Currently, researchers are looking closely at this mechanism in Weddell seals. These elite divers consistently dive to depths of nearly a quarter of a mile and stay submerged for up to 20 minutes. They display an impressive range of behavioral and physiological adaptations that make this possible.
Among these, high levels of myoglobin seem to play a large part in the maintenance of respiration during extended dives. This research team has now also established a tenuous but potentially compelling link between exercise and the associated release of calcium in muscle tissue and regulation of myoglobin levels within the cells. Simply put, exercise may lead to increased amounts of myoglobin within cells; high myoglobin levels lead to longer dives, and for marine mammals, this is a good thing.
It may be some time before we can fully explain why an adult whale, apparently alone and undisturbed, suddenly chooses to leap above the water to execute a perfect back flip. But for young humpback whales, where spending any of the dwindling supplies of maternal energy has to be justified, it may just be that leaping out of the water in a full breach, using all the newly developing muscles of their long flanks, increases the production of myoglobin. That in turn allows young whales to dive deeper and stay longer, resting beside their mothers in the deep, blue waters of Hawaii, as they ready themselves for the challenges of the impending migration north.
For now, our young baby whale performs, executing a perfect sequence of seven, eight breaches in a row, then slips under with just a glimpse of its little fluke. For the youngest humpback whales we see in Maui waters, a dive time of 60 to 90 seconds is typical, but as the season progresses and calves mature, breath-holding time extends to three or four minutes. For a calf of only 3 to 4 months in age, this is pretty impressive.
It may seem a strange contradiction that leaping out of the water leads to an increased ability to remain submerged. But for once, maybe the T-shirt slogan is right: at least for young humpback whales, life?s a breach and then you dive.
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