vignettes how whales feed

8/9/2019 Vignettes How Whales Feed

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How Whales Feed

Personal interview, later published as an article -- Gormley/Watkins, "How

Whales Feed." Sea Frontiers, May/June 1993.


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How Whales Feed

In Part Four of my book The WingedWhales (unpublished)I describehumpback feeding methods at

length. My narrative combinesprevailing interpretations of bubble-formations with some interestingalternatives given me by William A.

Watkins, a senior research specialistwhom I interviewed at Woods HoleOceanographic Institution. This

vignette explains why I used some ofWatkins' ideas and leaned away fromothers.

Watkins questions whetherthe bubble-formations of humpbacksare purposeful constructs. As oftenas not, he has seen humpbackssurface outside their bubble-nets. Asfor bubble-clouds, he concedes that sand lances or krill invariably swarm inside them,but did the whale blow the cloud for that purpose, or was it simply exhalingunderwater in an area abundant with prey on which it was feeding? He thinks bubble-clouds may result when humpbacks empty their lungs to make more room in theirthroat pouches for water and prey.

Were this the case, I should think humpbacks would exhale bubbles only near

the surface, just prior to sucking in prey, yet theyre often seen blowing bubbles farbelow the surface. Also, wouldnt Watkins' hypothesis apply to other rorquals?

Wouldnt we see finbacks, minkes, blue, sei and Bryde's whales releasing bubbles justas frequently? Ive seen finbacks releasing bubbles (rarely), but to the best of myknowledge, bubble-blowing is common only among humpbacks.

Sylvia Earle has found krill far more concentrated inside humpback bubble-netsthan outside. "Some such technique [bubble-net] is important to a successful hunt, fordespite their minute size [about two inches long] the krill are fast moving, as Idiscovered when I tried my hand at netting them. Using a fine-meshed dip net, Iscooped in the water where we could see krill swimming. My score after thirtysweeps was a meager three specimens. ... Later I tried scooping krill at the surfaceinside a whale's bubble-net. Suddenly I was krill rich. Each dip yielded dozens,sometimes hundreds, of the tiny creatures."

Watkins has seen underwater photographs of bubble-nets that were quitecrude, not at all the neat cylinders we see in artists' interpretations. But I've seenbubble-nets, as they were being blown, forming nearly perfect circles on the surface. Ican only assume they were just as well constructed underwater. As I see it, crudebubble-nets are made by whales with learner-permits. It must take time, years

Aerial view of a humpback b ubble-net off Cape Fanshaw,

Alaska. Wikipedia. J. Olson, NMFS/NOAA. In public domain.


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perhaps, to master the technique.I've often wondered why fish don't simply dash away, rather than allowing a

bubble-cloud to drive them to the surface. Could it be that bubble-clouds attract

rather than frighten prey? Might the prey be hiding inside the bubble-clouds? Watkinsdoubts it, but hehas seen sand lances apparently playing with bubbles, chasing andnipping them. Might they be mistaking bubbles for food?

Watkins feels that the hydraulics of cetacean feeding have been largelyoverlooked. For example, he believes that most odontocetes (toothed whales), ratherthan grasping prey with their teeth, merely suck prey in and swallow it whole, tail-firstas often as not. This suction process may involve a powerful diaphragmaticmechanism. It couldnt involve lung power, because theres no connection between acetacean's trachea and esophagus. Such a suction process would explain howrorquals like humpbacks can so quickly fill their enormous throat pouches with waterand prey.

This hypothesis makes a lot of sense. Many species of fish suck in their prey.And dolphins have been observed doing the same. The late George Nichols of ORES,describing fifty or more common dolphins feeding on squid near the continental shelfbreak just south of Georges Bank, reported that, "The groups of squid were broken up,individual animals were pursued and sucked in in an instant."

This process might explain how some captive bottlenose dolphins in Gulfport,Mississippi were able to spurt jets of water ten feet into the air with such accuracy that

Humpback whales north of Juneau, Alaska. This is a group of 15 whales that were bubble-net fishing on 18 A ugust

2007 . Author Evadb; Edit by jjron. Released into public domain.


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they hit my face nearly every time. Perhaps they were using their diaphragmaticsuction process in reverse. [See my vignette, "Spitting Dolphins."]

In the course of sucking in prey, cetaceans probably ingest a lot of seawater,and Watson thinks this may be one major purpose of the first stomach chamber. Afterthe food passes on, the animal can perhaps regurgitate the water.

Watson believes that all cetacean species use a similar "insuck" mechanismwhen feeding. Even sperm whales with jaws broken and cocked at a forty-five degreeangle still manage to feed and stay healthy, so it appears that the animals have littleneed of teeth for feeding. They probably just suck prey into their mouths.

While on the subject of sperm whales, let me add these fascinating notes.Watkins and some other observers think sperm whales may not swim around much atdepth. He thinks they may simply hover deep, their mouths smeared withbioluminescent slime from squid already eaten, thereby luring other bioluminescentsquid close enough to suck them into their mouths. Supporting this hypothesis is thesperm whale's habit, well known to old whaling men, of coming up at about the samespot where it dives. This suggests that it dives vertically and remains in one place untilit surfaces. Watkins says there is now evidence that sperm whales may be able toremain submerged for three hours or more!

Humpback W hale,Megaptera novaeangliae. Modified from public domain source

(http://www.photolib.noaa.gov/htmls/images/big/sanc0602.jpg) by en:User:Jdforrester and en:User:Ed g2s


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vignettes how whales feed

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