Schooling is related to the manifestation of stereotypic reactions 

 based on signal simplicity, speed and accuracy of action. Manifestations 

 of schooling behavior in pelagic animals of various taxons have a great 

 deal in common. The information which supports the schooling behavior 

 can pass through many channels. The motivation may also be varied. 

 Defensive motivation is most common: Schooling, an essentially little 

 structured system of behavior, is a useful defensive response when 

 pelagic animals are under attack by predators. The sequence of motor 

 events is adaptive and constant for the group, but the trigger (liberating) 

 stimulus for these behavioral programs can vary. It is assumed that the 

 formation of groups of any repetitive type is a manifestation of protective 

 reactions. Attempts to analyze schooling experimentally (Radakov, 1972; 

 Neill, Cullen, 1974 and others) have shown that schools definitely play 

 a protective role among prey animals. Among predacious fish, squids 

 ( Loligo vulgaris ) and cuttlefish ( Sepia officinalis ) , the absolute and 

 relative number of successful attacks on the prey decrease as the number 

 of fish in the field of vision of the predator increases. An increase 

 in the number of fish (prey) in a school retards the beginning of the 

 attack and makes the capture of prey by attackers more difficult. 

 Schooling of the prey dissipates the attention of the predator, confusing 

 the stereotype sequence of the individual stages of the chase, and the 

 attack is frequently not completed. The usefulness of the school when 

 the predators are herding types has been proven for squid (review: 

 Nesis, 1975) and fish (Radakov, 1972). 



Let us discuss the phenomenon of schooling in euphausiids and mysids, 

 in which it is frequently seen and has been relatively well studied, in 

 somewhat more detail. 



Among the euphausiids, phytophages predominate: Thysanoessa longipes , 

 J. i nermis , J. raschii , Meganyctiphanes norvegica , Euphausia superba , E. 

 crystallorophias , E. vallentini (Zelickman, 1961b, 1968b; Marr, 1962), forming 

 schools and clusters near the surface. A euphausiid school is a practically 

 single-species organized group of animals, recognizing each other (main- 

 taining distance}, of relatively homogeneous physiologic structure. Among 

 Barents Sea euphausiids, as exceptions, we observed three-species schools, 

 but always one species dominated. In most cases, the term "school" is 

 applied only to mature individuals. A school may be scattered by external 

 actions, after which it immediately reforms. The dimensions of a school 

 vary from a few meters (Nemoto et al . , 1969) to 30-100 m and greater 

 (Pavlov, 1974; Marr, 1962; Nemoto et al . , 1969). The shape of schools of 

 Euphausia pacifica , E_. similis , E. nana , T. inermis , according to Nemoto, 

 is species-specific. It seems to us that the larger the crustaceans, the 

 larger the size of the school. The largest schools, doubtless, are those 

 of E. superba ; the concentration in the school is up to 100 kq/m3 (Marr, 

 1962; Nemoto, 1968). School formation in euphausiids is an active process 

 (Zelickman, 1960a, 1961b; Zelickman, 1961), probably resulting from a 

 combination of causes. We consider school formation in euphausiids to 

 be a characteristic primarily of phytophages, which cast their spawn into 

 the water; the young of these species begin to feed on phytoplankton in 

 the first calyptopis stage. School formation occurs in the regions where 

 the young will feed; in any case, during the spring and summer biologic 

 season in the Arctic and, apparently, Antarctic waters, schools are always 



33 



