-109- 



interests, however, may be imported into the U.S.; the actual volume or 

 value is unknown. 



The significance of the tuna fisheries in the Indian Ocean relative to 

 other oceans to nations with long-range longline fleets may be reflected in 

 the proportion of total nominal effort that is expended in the Indian 

 Ocean. For the Japanese longline fleet, 15% of the total hooks set were in 

 the Indian Ocean in 1978; for the Taiwan fleet the most recent figure was 

 25% in 1976. This is in contrast to the middle and late 1960's with 

 relatively higher values of 27% for Japan and 50% for Taiwan. 



III. STATUS OF THE STOCKS 



III. A. Stock Structure 



It was assumed at the 1979 Shimizu Workshop (Food and Agriculture 

 Organization of the United Nations [FAO], in press) that there are single 

 stocks of albacore and bigeye tuna in the Indian Ocean. The yellowfin tuna 

 resource was believed to be composed of either two stocks (east and west of 

 about 100° E longitude) or a single stock. No information on skipjack tuna 

 stock structure was available for this report. 



III.B. Stock Assessment and Fishery Evaluation 



III.B.l. Trends in Catch- per-Un it-Effort 



Abundance indices have been recently computed for Indian 

 Ocean albacore, bigeye tuna, and yellowfin tuna over the period from 1952 

 to 1976 (Wetherall et al . , see footnote 1). 



The abundance index for albacore tripled in the first 

 few years of the fishery, but subsequently declined steadily to less than 

 10% of its peak value (Figure 7). The abundance index for bigeye tuna has 

 fluctuated moderately but generally shows an overall downward trend since 

 1952. The apparent abundance in recent years, however, is still about 50% 

 of its initial value (Figure 8). The abundance index for yellowfin tuna 

 has show a steady decline since 1954 to levels about 15% of the initial 

 values (Figure 9). 



Catch-per-unit-effort statistics are not available for 

 Indian Ocean skipjack tuna. 



