SOUTHWARD HO 



<N= 2,246) 



EXPLORATORY FISHING BY 

 R.V. VARUNA 



10 15 20 25 30 35 40 45 50 55 60 

 FORK LENGTH (cm) 



Figure 41.— Length-frequency distribution of Auxis sp. caught by 

 the Royal Venture and Southward Ho, in Philippine waters, 

 April-May 1975 (Rosenberg et al. see text footnote 9). 



ing catches of .4. thazard by type of gear, Sivasubrama- 

 niam also discovered that the size data from fish caught 

 by beach seine were biased. Because large A. thazard 

 present in the jjopulation were usually caught by other 

 gear, the size of fish taken by the beach seines was not 

 representative of the population of A. thazard in the 

 area (Fig. 44). Most often, medium-sized fish, varying 

 from about 28 to 44 cm were taken by this gear. The bulk 

 of the catch, however, consisted of fish in the 32-36 cm 

 length group. 



Trolling gear is effective in taking small tunas such as 

 Auxis as well as larger ones. Sivasubramaniam (1973) 

 observed that although trolling gear samples a very wide 

 size range of fish, it is particularly effective for A. rochei 

 in the 28-32 cm length group, a group for which none of 

 the other gears used has been effective. The smallest 

 bullet tuna were usually taken in waters around Beru- 

 wala or further south (Sivasubramaniam 1965). Com- 

 pared with size groups in the pole-and-line fishery, 

 which captured mainly fish in the 44-46 cm and 48-50 

 cm size groups, Sri Lanka's troll fishery exploited the 

 smaller ones— 26-28 cm, 32-34 cm, and 36-38 cm. 



The sizes of Atlantic Auxis do not depart appreciably 

 from those in the Pacific and Indian Oceans. Figures 45 

 and 46 show the percentage frequency distribution of 

 lengths of A. rochei caught in various years at the Bar- 



Figure 42. — Location of exploratgry drift-net catches by the RV 

 Varuna off southwestern India, and the length-frequency distri- 

 bution and average weights of Auxia thazard and A. rochei in the 

 catches (Silas 1969). (A', = number of fishing operations; S, = 

 number of specimens.) 



bate, La Linea, and Tarifa trap net operations in Spain. 

 Rodriguez-Roda (1966) reported finding two size groups 



in the Barbate and Tarifa samples — one around 38.5- 

 39.5 cm — and the other at about 45 cm — and hypothe- 

 sized that these two groups may possibly correspond to 

 two age groups. Furthermore, he noted that at La Linea, 

 the smaller group was at 40.5 cm and the larger at 42.5 

 cm. This led him to suspect that two distinct popula- 

 tions of A. rochei may be involved in the catches at these 

 localities. Rodrigues-Roda found no significant sex- 

 related differences in the length-frequency distributions. 



4.2 Abundance and density 



4.21 Average abundance 



The relative abundance of Auxis in Japanese waters 

 off Ashizurimisaki and Tosashimizu was discussed by I- 

 shida (1972a). Using data collected in the Auxis pole- 

 and-line fishery from October 1964 to June 1967, Ishida 

 found two peaks in the average number of vessels 

 operating per day each month. The first p)eak occurred 

 in March and the other in October, and during these 

 months about 200 vessels/day participated in the fishery 

 for Auxis. 



45 



