46 UNDERWATER GUIDE TO MARINE LIFE 



Second, if a number of species, all of which possess the same distasteful 

 or dangerous attributes, come to resemble each other, the association of dangerous 

 qualities with their appearance is made simpler for the predator, that is, learning 

 is reinforced. Perhaps this is why the distasteful sea slugs (nudibranchs) look 

 so much alike and are so brightly colored. 



ANIMAL BEHAVIOR 



The purpose of this section is to give some understanding of the principles 

 involved in activities of marine animals as they adjust to their environments. 

 The stories of fish behavior told by fishermen and others who come in contact 

 with the sea are often interesting and fascinating, but for the most part they 

 have been greatly misinterpreted. Often human qualities have been attributed 

 to fishes and superficial conclusions drawn from only bits of behavior. To the 

 diver who has to deal with the aggressive fishes in their environment this can 

 be dangerous. A more rewarding approach can be taken by careful scrutiny 

 of the evidence available. This involves looking into the physical and mental 

 equipment possessed by marine animals, into the kind of behavior one can 

 expect with a particular type of nervous system possessed by an animal, and 

 into the part that sense receptors (visual, olfactory, etc.) play in their total 

 behavioral adjustment to their environment. 



It may become apparent to the underwater naturalist as he studies the marine 

 animals and their environment that these animals do not perceive their 

 environment as the diver does. Many of these animals are deaf (the starfish, 

 worms and snails, and probably some fishes). Many are blind, others have poor 

 vision (sharks and rays), and some have excellent vision (some bony fishes, 

 squids, octopuses). It is suspected that some fishes can hear sounds of higher 

 frequencies than humans. Most fishes, such as the bottom feeders, have a 

 highly developed sense of smell and are able to detect very weak chemical 

 concentration. It becomes clear that the underwater world as seen by the diver 

 appears different to each species, and what sometimes appears to be bizarre 

 coloration, shape, or behavior in a fish to the diver can be explained as a method 

 of survival adapted to the sensory and motor abilities of the animal that feeds 

 on it. The diver perceives the underwater world mainly through vision. Man's 

 vision underwater is far superior to that of fishes. He is very sensitive to color, 

 he can focus over a wide range of distances with excellent visual acuity, and he 

 is a good judge of distance because of binocular vision. But he is limited when 

 compared to most fishes, for their behavior depends upon smell and lateral line 

 receptors for contact with the environrnent. Man cannot smell underwater nor 

 can he detect vibration as fishes can over great distances. This makes man 

 primarily a day animal in the sea, for at night, unless he brings a light source 

 with him, he loses his visual superiority and becomes as helpless as a fish out 

 of water. 



Marine Invertebrates 



The behavior of marine invertebrates is for the most part dependent upon the 

 type of structural equipment (action equipment, sensory receptors, nervous 



