Tuesday, April 16, 2013

Play and porpoise

Originally written for Carolina Style, a magazine based in Wilmington, North Carolina, which went belly up before this could see print. (c) 1995 Frederick C. Ingram. All rights reserved.

(c) 1995 Frederick Ingram

Dolphins captured the imagination of humans a long time ago.  They seemed to have swum from the heavens, coursing through the water as effortlessly as the swans pulling Apollo's chariot.  The ancient Greeks, Minoans, and Cretans considered them the missing link between themselves and gods, and commemorated their form in sanctuaries, frescoes, and even decorations on domestic utensils. 

Dolphins haven't missed the boat in modern mythology, either.  Consider the film The Big Blue, about a diver who literally considers dolphins his family.  His wallet is full of their pictures.  They can be cute, particularly "neonates"--newborns less than a month old that still show crease marks from where their fins were folded inside the womb.  These calves stay with their mothers until they are three, six, or even ten years old, when they join gangs of juvenile dolphins.  This is a long period of dependence for animals that, in the wild, may live to reach 50.  It is also a long period to learn from your elders.

Fin of an adult dolphin swimming next to a neonate (left). (c) 1995 Frederick Ingram

Their streamlined shape makes them the most efficient marine mammal, twice as efficient as seals and ten times as efficient as humans.  They begin utilizing pressure waves, such as those created by ships, as newborns riding close to mamma.  It is only natural that in our century, the century of the airplane, streamlining captures the imagination.  What is difficult to capture is that these graceful creatures weigh five hundred pounds. 

Our affinity for them seems quite logical.  Like us, they are quite social animals.  But then, so are termites.  Of course, part of the dolphin's charm lies in its intelligence, but this is difficult to measure.  Dolphins have a higher than average ration of brain mass to body mass, a distinction they share only with the primates among mammals.  Their brains are more convoluted than any other mammal, including humans.  However, their cerebral cortex is only half as thick as ours.

The external manifestations of genius are more apparent.  In one amazing story, retold by Susan Shane in Sea Frontiers, it is easy to see why researchers feel such a bond with their subjects.  Two captive bottlenose dolphins teamed up to capture a moray eel living in a rocky crevice in their tank.  One caught a scorpionfish and poked the moray's rear end with it, driving it out of the rocks to the arms of the other dolphin.  Not only are they intelligent, they are either brave or crazy.  They have to watch it, though, as they have been known to fall victim to sting rays' spines.  Female dolphins in Monkey Mia, Australia carry sponges in their teeth while foraging, ostensibly a buffer against poisonous fish.

To the ancient sailors, this intelligence must have made them stand out eerily against the fish usually encountered, such as the dolphin fish, or mahi mahi, which is not an intelligent mammal at all but a big, dumb, easy-to-catch fish with a very mild taste.  How many times have waiters been frustrated by the homonym!  "It's not Flipper!" is a familiar refrain at restaurants with dolphin on the menu; I prefer to call the gilled fish by its Hawaiian name.  One person who did like to eat dolphin-the-toothed-whale-like-Flipper was Queen Elizabeth I of England.  Any corpse of "The Queene's Fishe" that washed up on shore had to be sent to her cooks immediately.  The law still stands, but the carcasses are turned over to the British Museum, which, understandably, has amassed a large collection of whale skeletons.  The meat is said to taste like "steak fried in cod liver oil" as researcher Karen Pryor noted in the collection Dolphin Societies.  Some fisheries in Peru still specialize in it.

Dolphins have been seen as playful since ancient times.  The Greek god Bacchus (or his Roman incarnation, Dionysus) has been associated with them in the following myth:  while he was travelling on a ship loaded with grapes, the crew conspired to sell him into slavery.  When their plot was discovered, the crew threw themselves overboard as the oars turned into snakes and the ship became overgrown with vines.  After the sailors repented, Bacchus turned them into dolphins to save them from drowning.

The dolphin's clicks, chirps, whistles, and gestures are often intended to mean something different than what humans perceive, however.  A playful flap of the fluke can indicate annoyance.  But humans seem unwilling to see the aggressive side of dolphins.  Some of the most dramatic social displays, such as leaping into the air, may be contests of dominance. 

Strand feeding

Some of their clicks and whistles may not be as friendly as they seem, in spite of the very wide grin.  Nevertheless, these sounds enable the dolphins to communicate and to function effectively as a pack.  Their capacity for cooperation is well demonstrated in a unique activity called strand feeding, which is performed by only a few groups of dolphins, including those near Hilton Head Island, S.C.

(c) 1995 Frederick Ingram
In strand feeding, a group of one to six dolphins makes a wave to drive a school of fish onto the shore.  In order to strand the fish, the dolphins suddenly move close to each other and rush towards the bank with great force.  This exertion creates a wave which lands the small fish on the shore.  The dolphins then slide themselves completely or partially out of the water and snap up the fish with a few quick neck movements.  "It's quite impressive," observes Pam Sandsmark, a volunteer who helps monitor the dolphins.  It's also quite clever.  These dolphins truly seem to be in their element, be it water, air, or mud.

Strand feeding requires a unique location.  There is often a ledge underneath the water to help the dolphins scoop the fish up.  The dolphins understandably tend to avoid sliding up on oyster beds.  It occurs around the clock, usually within an hour or two of low tide, when the mud flats are exposed.
Strand feeding can be risky.  Although dolphins have surprisingly agile necks, mobility on land is hindered.  Dolphins typically thrust a pectoral fin into the soft mud to help.  There is the possibility of becoming stranded oneself, or of suffocating, since water itself supports the dolphin's internal organs.  There are other ways for dolphins to catch dinner.  Their sonar can stun some fish.  Some in Florida use their flukes to slap fish up to thirty feet in the air.  Many dolphins have learned to trail boats, particularly shrimp boats, which stir up fish along the ocean's floor.  The behavior is related to barrier feeding, or using underwater ledges to corral fish.  The turbidity of the water is now believed to be a prime factor.

Cara Gubbins, a University of Nevada researcher, is studying these dolphins and how they utilize their environment.  "Behavior always occurs in some type of context," she states.  "Behavioral ecology stresses the context."  Although she cautions that it's difficult to predict the outcomes of scientific research, she and many others are interested in learning what are the key pieces of habitat for the dolphins.  "By finding out how different subgroups--nursing mothers, for example--use their habitat. . . we can find critical areas to conserve for the species."  For example, the waters around Hilton Head appear to be a critical breeding area for the bottlenose dolphin.  She has seen several newborn calves in the area, some a few hours old.  "It might be an important nursery area," she states, although she has not been in the area long enough to be certain.  Wary of the plight of transient bottlenose dolphins, she is also curious to know how they interact with resident dolphins.  The transient dolphins lost half their population in the late 1980s in what has been attributed to poisoning by red tides, microbes that release a toxin affecting the nervous system (although some maintained the cause was viral contamination by medical waste).  She would like to find out if one group can fill out its population losses with individuals from another. 

In order to monitor the dolphins and their interactions, Gubbins and her assistants document each dolphin sighting by the number encountered and the behavior observed.  Gubbins photographs the dorsal fins of the animals, which have a variety of natural patterns and notches on them.  Identifying age is more difficult, but older individuals do tend to look more weatherbeaten, their beaks as dented as the propeller on an old cropduster. 

Although only the resident population of bottlenose dolphins are known to strand feed, "there is a strong possibility that feeding strategies are culturally transmitted," says Gubbins.  There are several clues to this.  Since it often occurs in pairs, there is a potential that one of the dolphins could be teaching the trick to the other.  This possibility is reinforced when there is a considerable size difference between the two, suggesting the smaller is an apprentice.  However, little is known about how this knowledge is transmitted, even though bottlenose dolphins are perhaps the most studied of all the whales.  Orca parents in Patagonia are known to teach their young to strand feed, beaching themselves dozens of times in demonstration on shores devoid of prey.

To those that have witnessed strand feeding, the most amazing aspect is its utter suddenness.  The dolphins give the observer absolutely no warning before rushing the shore, yet they all move as one.  Experiments with underwater microphones have been unable to discern any audible cue.  Researching strand feeding could unlock many other mysteries.  Why do the dolphins almost always strand themselves on their right side?  Are they capable of teaching each other?  How do they accomplish their, er, "schooling"?  They have already let us know one thing for certain:  we have much to learn.
Self-portrait of the author ca. 1995. (c) Frederick C. Ingram