Figure 52. — Distribution of surface temperatures in July- 

 September in years of good (A) and poor (B) fishing (or A axis 

 rochei at Tosashimizu. Kochi Prefecture, Japan (Y'asui 1975). 



fluenced to a large extent by a seasonal in-migration of 

 fish from the west and south. 



At Hachijo, where Auxis are landed by surface troU- 

 ers, catches are made throughout the year except in Oc- 

 tober (Fig. 51). Yasui (1975) observed that there are two 

 seasons for Auxis at Hachijo — one in April-August and 

 another in November-January. The appearance of A uxjs 

 in April-May at Hachijo coincides with the end of the 

 gill net fishery for flyingfish, which are preyed on by 

 Auxis. Yasui also noted that sexually mature fish appear 

 in the catches in April-May followed by larger, older fish 

 in .July. 



At Ashizurimisaki in Kochi Prefecture, Ishida (1972b) 

 noted considerable fluctuations in landings of Auxis. To 

 determine the possibility of predicting the degree of suc- 

 cess of a fishing season, Ishida, using data for 1952-67., 

 obtained the following: 



C, = catch in October-March in year; 

 Cj+, = catch in October-March in year; + 1 

 ACjti = difference between Cj and C,»i. 



Plotting C, against ACj»,, Ishida found that when C, 

 was small, AC, + , tended to be positive and vice versa. 

 Ishida also noted that larger catches of Auxis tended to 

 be associated with cooler temperatures. Yamashige 



(1974), on the other hand, found a positive relatonship 

 between catches of A. rochei in August- July and the dif- 

 ference in the mean surface temperature between 

 August and October of a given year, and he described 

 the relationship between these two variables as follows: 



y = 1.42 + 1.15 ((g - t,o) 



where Y = catch, in 1,000 t, from August {n year) to 



July (« + 1 year) 

 tf^ = mean surface temperature in August at 



Ashizurimisaki (°C). 

 t^^ = mean surface temi>erature in October at 



Ashizurimisaki (°C). 



In Sri Lanka, the mechanization of fishing boats 

 made fishing jjossible even during periods of monsoons 

 and has been primarily responsible for a shift in the fish- 

 ing season. Originally, Williams (1963) reported that the 

 main fishing season for Auxis in Sri Lanka extended 

 from October or November to May. Sivasubramaniam 

 (1973), however, found that Williams defined the fish- 

 ing season by examining catches made during the north- 

 east and intermonsoons when beach seines are usually in 

 operation. Excellent fishing occurs in all fishing areas 

 around Sri Lanka particularly during the end of the 

 southwest monsoon. Sivasubramaniam observed that 

 this period is associated with heavy recruitment and 

 vulnerability of the recruits to trolling gear. The result is 

 that the number of fish caught per day rises abruptly, 

 but the net tonnage landed, does not rise proportion- 

 ately. 



5.4 Fishing operation and results 



5.41 Effort and intensity 



In the Auxis fishery off Ashizurimisaki in Kochi Pre- 

 fecture, Japan, fishing intensity (the number of small, 

 3-gross ton pole-and-line boats operating per day) varies 

 widely from as few as 10 to as many as 260 boats/day 

 (Ishida 1972a). Fishing intensity usually peaks once in 

 March and again in November to about 200 boats/day. 

 During the balance of the fishing season, which extends 

 usually from October to May, however, the average 

 number operating is about 170 boats/day. 



5.42 Selectivity 



Although pole-and-line fishing is effective for skip- 

 jack and yellowfin tunas, it is not equally effective for 

 Auxis. Sivasubramaniam (1973) observed that in Sri 

 Lanka, Auxis respond poorly to chumming probably 

 because the live bait used is larger than the most com- 

 mon food items in their stomachs. 



The drift net, which is in operation around the entire 

 island of Sri Lanka, is also ineffective at times par- 

 ticularly for Auxis <30 cm. It is, however, effective for 

 skipjack and large kawakawa. Catches of Auxis by drift 

 nets, therefore, amount to only about 18 kg/day for a 3.5- 



53 



