Tuesday, 30 August 2011

Thoughtful Sharks : Knowing Others as Individuals


In Tahiti, I observed the reef sharks inhabiting the nearby lagoon. They soon accepted me into their community, and by noting the behaviour of each individual in a variety of situations over a period of many years, I found an unknown dimension of their lives, never before observed or documented. This included much evidence that the sharks were using cognition, or thinking, in their daily activities, rather than the automatic stimulus/response reactions that had been assumed to control their behaviour.

To illustrate the difference between automatic behaviour and cognition, consider a calculation. The act of calculating, which is so easily and swiftly accomplished by computers, is analogous to automatic behaviour. But understanding the reason for the computation requires cognition, which the computer will never achieve.

Various domains of science use different definitions of cognition, but for me as an ethologist, the most straightforward definition is : the purposeful manipulation of mental representations. (For more information, see the section on cognition on my website at: www.theplayoflife.org or the chapter "More on Thinking in Animals" in my book.)


Recognition of others as individuals has long been established in fish and sharks, and is necessary for the complex social lives in which cognition is most evident.

In the sharks I observed, the tendency of the blackfin reef sharks (Carcharhinus melanopterus) to travel with favoured companions, was one indication that they knew each other as individuals. An unusual and telling example involved the visits of two elderly female companions to my study area each year for four years, during the dark of the moon at the end of April, and at no other time. They came together and left together, and I never learned where they came from, so it must have been very far away. For the last two years they were accompanied by a third elderly shark whose home range was about two kilometers farther along the lagoon. Unlike them, she returned every few months after her initial visit to the region.

I documented many other companionships, showing that both female sharks and the males, who lived in the ocean beyond the lagoon, had favoured companions of the same gender. Each individual was different. Some sharks often travelled alone, and others changed companions relatively frequently. Often, companions were joined temporarily by residents of the regions through which they travelled.

One shark who tended to be a loner, joined two companions whose home ranges over-lapped hers, when the three ventured into a new, and possibly uncertain, situation. They approached in triangular formation, the loner taking the position in front of the companions, who followed swimming side by side, equidistant from her and from each other. I saw the same three sharks take this formation on several occasions over the years, always in new circumstances.

Observations that at least some species of sharks and rays choose which members of the opposite gender with whom they wish to mate, provides further evidence that they know each other as individuals.

All fishes have elaborate forebrains, and the degree of forebrain development has been correlated with social behaviour and communication, abilities which are integrated with cognition. Fish continue to develop neurons throughout their lives and do so at a faster rate in a stimulating environment, indicating a link between experience and neural development. Studies indicate that the ratio of brain to body size in sharks overlaps that of mammals and birds, and learning is considered to play an important role in their lives.

Memories are invoked in learning, and the memories of facts that are available for mental reference are called declarative memories, indicating consciousness. Several researchers have concluded that learning in fish calls on declarative memories and that fish are conscious animals.

That a particular shark will seek out and return to just one other shark in its travels, among all of the sharks present, is one example of a situation in which the animal is referencing declarative memories—the memories of the companion. I have seen a visiting shark arrive with its companion, in a place where many other sharks were circling, and swim nose to tail, or in parallel with, one shark after another, socializing over long periods before rejoining the companion with which it had arrived.

But my observations were cut short when the population was finned for the shark fin soup market. While they were being massacred, I wrote down their story so that the world would find out what they were like and what happened. The exciting story of this mysterious community beneath the sea, that was terminated by a shark finning company from Singapore, is recorded in my book: "My Sunset Rendezvous : Crisis in Tahiti."


The sharks' capacity to think and feel provides another crucial reason to save them from extinction, as well as their importance ecologically.  Knowing of their cognitive abilities, shark behaviour will never seem the same again, and the world-wide, barbaric massacre of sharks for the profit brought in by just their fins, becomes even more tragic. 


©  Ila France Porcher
author of "My Sunset Rendezvous : Crisis in Tahiti"


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