236 Fish Behavior and Angling 



Parts of home ranges may be considered territories which are defended 

 against the encroachment of all fish except those much larger than the 

 defender. This is particularly true during the spawning season among 

 fishes that build nests. 



No one has yet been able to define the roles of hearing, the sensory 

 perception of semicircular canals, the kinesthetic senses, and the lateral 

 line senses in orientation or homing, although auditory organs and the 

 lateral line organs are believed to supplement vision and olfaction in 

 helping to locate objects at a distance. These objects may be moving and 

 thereby create mechanical disturbances or their presence and location 

 may be perceived and accurately computed from the time relations of 

 reflected water waves set up by the swimming movements of the fish 

 itself. In moving water the presence of deflecting objects is readily 

 recorded. This type of sensory perception is extremely important in turbid 

 water where vision is impaired. 



Theories of Migration in Fishes 



It has been shown that vision and olfactory senses have a role in 

 orientation and home-range recognition. Hasler, et al.,^^ have modified 

 the classification of Griffin ^^ to define the types of abilities required by 

 fish that return home from varying distances: 



Type I: The ability of an animal to find its way home by relying on local 

 landmarks within familiar territory and the use of exploration 

 in unfamiliar areas. 



Type 11: The ability to maintain a constant compass direction in un- 

 familiar territory. 



Type III: The ability to head for home from unknown territories by true 

 navigation. This involves a "sextant" type of mechanism. 



The homing movements of displaced warm-water fishes are operative 

 over relatively short distances as compared with the spawning (homing) 

 migrations of such fishes as salmon, eel, and some other marine fishes. 

 These fishes are able to migrate many thousands of miles and return with 

 some precision to specific spawning locations where they themselves were 

 hatched. Such migrations may involve the three types of homing abilities 

 listed above: for identifying local landmarks and exploring, for main- 

 taining a fixed direction in unfamiliar territory, and for true navigation. 



The migrations of the salmon have been studied more than any other 

 fishes and serve to illustrate the complexity of these spawning movements. 

 Salmon are spawned in cold-water streams tributary to the oceans and 

 move downstream into salt water where they spend 2 to 7 years at sea 

 depending on the species. When they reach sexual maturity, they return 

 to the same rivulet so consistently that populations in streams not far 



