98 



Fishery Bulletin 100(1) 



All types 



Figure 4 



Bycatch (t) per 1000 t of target species by school type for 

 the Soviet tuna purse-seine fishery. Dots are means, bars 

 are 95'>'f confidence intervals. 



sible. Whales often remain in the net until the end of purs- 

 ing and then escape from the purse seine by either diving 

 under the purse line, by ramming through the net wall, or 

 by sinking the corkline (a rare occurrence). 



Observers registered a single case of entanglement in 

 the net and subsequent death of a young sei whale about 

 10 m in length and about 12 t in weight. The dead animal 

 was taken up on the vessel's deck, released from the purse 

 seine, and discarded into the ocean. It is not possible to as- 

 sess the frequency and probability of whale mortality by 

 the purse-seine fishery in the WIO. 



There were 1 7 species ( or groups ) of marine animals iden- 

 tified in the catches of whale-associated schools (Table 4). 

 Salps, ctenophores, and batfish (Platax spp.) were consid- 

 ered accidental bycatch, whereas long-finned fathead (Cu- 

 biceps pauciradiatus) was a prey item of both tunas and 

 whales. Nontuna bycatch in this type of association aver- 

 aged 0.306 ±0.344 t for a positive set or 10.891 ±15.787 t 

 per 1000 t of target species (Figs. 3 and 4). Sharks of the 

 genus Cairharhiniis and Isui-iis made up the bulk of the 

 bycatch in whale-associated school .sets (0,289 t/10.302 t) 

 (Tables 4 and 6). 



Log-associated schools 



Log-associated schools are one of the predominant school 

 types found in the WIO all year round (Table 2, Fig, 2, A 

 and B). Sets on log-associated schools were made through- 

 out the sampling area as far south as 15°S (Fig. ID). In 

 log-associated schools the bulk of the catch were skipjack, 

 yellowfin, and bigeye tunas — 6Ty( , 2A'7i . and y?( . respec- 

 tively (Table 5). Log-associated schools in all cases con- 

 sisted of several fish species. Bycatch was found in 93% 

 of the sets, and nontuna bycatch in 87%. The absence of 

 bycatch was rare, observed only during successive sets on 

 the same floating object. 



The species composition associated with floating objects 

 was the most diverse of any set type and included 45 spe- 

 cies (or higher taxa of fishes) (Table 4). Nontuna bycatch 

 was at its highest in log-associated sets, as much as 0.780 

 ±0.144 t per positive set or 41.337 ±14.281 t per 1000 t of 

 target species (Figs. 3 and 4). The bulk of the bycatch in sets 

 on log-associated schools was made up of rainbow runner. 



