248 POPULATIONS OF THE SEA 



dominated fish swims out of the way of an aggressive fish e\'en 

 when it is not displaying or threatening. They learn each other's 

 status so that a fish can threaten those lower in the hierarchy 

 without being threatened in turn. An order of supersedence or 

 precedence thus develops, and this is related to the order of 

 dominance. 



The order within the community was consistent and suggested 

 to Miss Brawn that the fish knew each other individually and were 

 aware of their status in relation to others. The average distance 

 at which one fish of a pair erected its dorsal fins (a sign of tear) 

 and moved out of the path of slowly approaching but nonthreaten- 

 ing "superior" fish was 36 cm, the maximum 122 cm. 



Some changes took place with time, and the relative status of 

 the more dominant was occasionally reversed, but by and large 

 the aggressive nature of individual fish and the order of dominance 

 retained the same characteristics from one year to the next, in 

 spite of a long summer period when aggression and differences of 

 "social level" w^ere absent. 



Both sexes are aggressive during the peak period of aggression 

 in the autumn and indiscriminately against each other; but in the 

 immediately prespawning time aggression is shown only by the 

 males and against other males and unripe females. 



A number of large fish were closely studied during the 1957 

 spawning, from 4-15 March. Three weeks before this period the 

 dominant male fishes set up territories, which they defended 

 against all intruders. Differential responses were given to fish 

 entering the territory and so far as could be seen these were based 

 solely on the behavior of the intruding fish. If a female ready to 

 spawn or approaching spawning condition entered the territory 

 she did so relaxed, swimming slowly, and showing no fear. Males 

 did so quickly, reacting quickly to threat display by returning it, 

 by flight, or other fear responses. 



Once the sex of the intruder is recognized as female the male 

 "flaunts" or "displays" at a distance of about a foot, and if the 

 female is ripe and ready to spawn the sequence is "flaunting" 

 followed by curious movements accompanied by prodding and 

 grunting for some 10-15 minutes, actions all directed toward 



