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These are some of the dozens of humpback whales who make their summer home the pristine, fish-filled, waters in the vicinity of Juneau. These huge, but graceful, creatures have migrated from Maui (some 3,000 miles/5,000 km away) each Spring to feed on the rich ecosystem of our waters. Averaging over a ton a day of mostly herring for each whale, these 50 foot/15 meter and 50 ton behemoths will feed nearly continuously all summer. This is in preparation for the long Fall swim back to Maui where there is virtually no food, but the warm waters are supportive of birthing offspring.
Humpback whales are born during the winter months and weigh between one and two tons and are about 15 feet (5 meters) in length when they take their first breath. However they are very lean - virtually no fat. Thus they would perish from hypothermia if born in the cold northern latitudes of Alaska. They will gain the protection of warmth from blubber rapidly as they begin nursing from their mothers prior to the long journey north, and will continue to nurse until after return to their winter home off Maui. The following return to Alaska will find them over 20 tons in size.
As with all "little ones," the baby whales have not a care in the world, and when they are not nursing (which is FORTY times per day), we are sometimes lucky to catch "play-time." The picture below is of a BABY humpback practicing breaching. When we are lucky, we'll see them do this over and over again, interrupted sometimes by "mama" showing how it's REALLY done!
Normally during summer they are single (except, of course, a cow and calf), but sometimes group together for cooperative feeding. This is called "bubble-netting." In this behavior one or two will swim in a deep circle while exhaling a near continuous stream of bubbles. This vertical column of bubbles acts much like a fish net. Small schooling fish, most often herring, become confused and will not swim through the bubbles. Meantime, the rest of the pod (I myself on one occasion counted seventeen), does a lot of "singing" and begins a rapid ascent with each of their 12 foot jaws wide open, and break the surface nearly in unison. (see picture below) In addition to the awesome visual sight, SCANIA will normally deploy her hydrophone during these periods so all aboard can listen to the nearly continuous whale songs.
They then close their mouths, force their tongues against the stringy baleen to get rid of excess water, and then slowly swallow their meal through their narrow (about 9 inches/25 cm diameter) throats. The picture above was after such an episode. Note all the gulls in the vicinity who will feast on the small fish that escape the whales but are too near the surface for too long.
The whale in the center still has his/her mouth wide open, and will not slide back down beneath the surface until after closing it.
As the whales swim on the surface, each inhale/exhale involves some 80% of lung capacity (compared to about 25% for humans and land mammals). Whales are very efficient at oxygen storage, as blood makes up to 15% of their body mass - which is double that of humans. Then when the whale dives, it slows its own heart rate substantially - further rationing oxygen depletion. They can rapidly swim to extreme depths, as increased pressure causes the whale's lings to collapse, and forces any residual air into its blowhole, and thus are not subject to the "bends" as are human divers. Although a Humpback can remain submerged well over thirty minutes, five to ten minutes between dives is much more typical.
