BEHAVIOR OF BLUEFIN TUNA SCHOOLS IN THE EASTERN NORTH 

 PACIFIC OCEAN AS INFERRED FROM FISHERMEN'S LOGBOOKS, 



1960-67' 



J. Michael Scott^ and Glenn A. Flittner" 



ABSTRACT 



Fishermen's records of 8,059 purse-seine sets made on Thunnus thynnus (bluefin tuna) 

 were examined for the period 1960-67. A total of 3,588 sets were identified as to school 

 type. The majority of these sets were made within 90 miles of the beach off southern 

 and Baja California from lat 23°N to 34°N. The region was divided into a northern 

 and southern area on the basis of biological and oceanographic factors. 



Significant differences were observed in the occurrence of the six most common school 

 types between ^he northern and southern most areas of the fishery. The difference in 

 occurrence of the jumping, boiling, and shining schools was related to the relative absence 

 of red crabs (Pleuroncodes planipes) in the northern area and to differences in the for- 

 aging behavior of T. thynnus on baitfish and red crabs. 



Differences in vulnerability to capture and catch per successful set were noted among 

 the five most common uaytime schools as well as with respect to time of day. 



Purse-seine sets made with the assistance of airborne spotters had larger catches and 

 a greater percentage success than did unassisted sets. In addition the percentage of a 

 particular school type taken with aircraft assistance was inversely proportional to the 

 visibility of the schools from the mast. 



The existence of different school types in scom- 

 broid fishes has been noted by several authors. 

 In 1931, Suzaki (as cited by Uda, 1933) rec- 

 ognized five types of skipjack tuna {Katsuivomis 

 pelamis) schools in the western tropical Pacific. 

 Kimura (1954) listed six types of skipjack tuna 

 schools. To these Inoue (1959) added three ad- 

 ditional types based on behavior and association 

 of the tuna with animals and inanimate objects. 

 Ogilvie (1949)' described 10 types of tuna 



^ This work was initiated while both authors were 

 employed in the Tuna Resources Laboratory of the Bu- 

 reau of Commercial Fisheries (now the National Marine 

 Fisheries Service, Southwest Fisheries Center) under 

 the direction of Dr. Richard R. Whitney, then leader of 

 the Tuna Behavior Program. 



" Department of Zoology, Oregon State University, 

 Corvallis, OR 97331. 



' Bureau of Marine Sciences, San Diego State College, 

 San Diego, CA 92115. 



* Ogilvie, H. 1949. Description of various types of 

 tuna schools, of behavior, methods of fishing and pro- 

 duction possibilities in relation to pole and line fishing 

 encountered in Central America. Inter-American Trop- 

 ical Tuna Commission, La Jolla, Calif. 5 p. (Manuscr.) 



Manuscript accepted April 1972. 



FISHERY BULLETIN: VOL. 70, NO. 3, 1972. 



schools commonly encountered in the eastern 

 tropical Pacific. McNeely ( 1961 ) stated that the 

 California tuna fishermen recognized several dif- 

 ferent school types for yellowfin (Thunntis al- 

 bacares), skipjack, and bluefin tuna {T. thyn- 

 nus). Scott (1969) described 16 different school 

 types for the eastern Pacific tunas, listed fish- 

 ermen's synonyms, and placed them into two 

 major groups and five lesser categories on the 

 basis of time of day, depth of occurrence, and 

 association with other animals and floating ob- 

 jects. 



Various attempts have been made to correlate 

 the type of school with fishing success. Uda 

 (1933) and Uda and Tukusi (1934) attempted 

 to show an "index of biting" for the different 

 school types as did Kimura (1954). Inoue 

 (1959) correlated the percentage success of the 

 Japanese purse seiner fleet with school types for 

 yellowfin, skipjack, and bluefin tuna in the west- 

 ern tropical Pacific. Inoue's data indicated that 

 possible differences in school size and vulnera- 



915 



