July 1966 



COMMERCIAL FISHERIES REVIEW 



11 



An analysis of available data froni American Samoa indicates that catch per unit of ef- 

 fort, in terms of numbers of albacore taken per 100 hooks fished, has not shown any upward 

 or downward trend during 1963 and 1964. On the other hand, the weight of albacore landed 

 per 100 hooks declined significantly in 1964 (fig. 3). The decline was largely due to a de- 

 crease in mean size of fish taken by the fishery in 1964 as compared to 1963 and earlier (fig. 4). 



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 1963 1964 



Fig. 

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3 - Catch per 100 hooks of albacore, in niambers and in weight, 

 1963 and 1964, from data of vessels based at American Samoa. 



The available data indicate that the 

 catch of albacore tuna has decreased in 

 recent years, mostly in terms of weight 

 of fish taken per unit of fishing effort. 

 The decrease in mean sizes of albacore 

 in 1964 was due to a complete change in 

 size composition from 1963. The very 

 smallest fish available to the fishery in- 

 creased sharply (albacore under 85 centi- 

 meters or 33.5 inches in length numbered 

 an estimated 9,045 in 1963 and 88,509 in 

 the 1964 catches) and the numbers of the 

 largest fish decreased (63,183 fish larger 

 than 100 centimeters or 39.4 inches in 

 1963, but only 35,273 in 1964). In other 

 size categories, fish between 86 and 90 

 centimeters (33.9 to 35.4 inches) increased 

 greatly from 101,299 in 1963 to 214,826 

 in 1964, while fish between 91 and 100 

 centimeters (35.8 to 39.4 inches) decreased 

 from 606,586 to 307,908. 



Although changes in sex ratio, as well as shifts in fishing grounds, could greatly affect 

 the mean sizes of fish taken (the average weight of male albacore is 4 to 10 pounds more than 

 that of females; size of albacore in the South Pacific increases progressively from the Equa- 

 tor to around latitude 25° S.), the data for 1963 and 1964 indicate that those factors played on- 

 ly a small part in the size decrease of 

 1964. The proportion of male albacore 

 tuna decreased only slightly from 64.3 

 percent of the sampled fish in 1963 to 62.1 

 percent in 1964. Similarly, the fishing ef- 

 fort in the area between latitude 15° S, 

 and latitude 25° S., where the albacore 

 are the largest, decreased slightly from 

 15.4 percent of total fisTiing trips in 1963 

 to 12.1 percent in 1964. 



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 962 19li3 19<S4 



It appears that the decline in catch 

 rate, in terms of weight of albacore taken 

 per unit of effort, has resulted primarily 

 from (1) same presently unexplainable 

 movement of larger fish away from the 

 areas of the fishery, particularly during 

 February-May 1964, and (2) the entrance 

 into the fishery in early 1964 of an abun- 

 dant year-class, A preliminary analysis 

 of the data suggests that the strong year- 

 class contributed in large part to the de- 

 cline in catch (weight) per unit of effort. 

 If so, it may be expected that the catch (weight) per unit of effort will rise in subsequent sea- 

 sons as the large year-class passes through the fishery. 



This report is based largely on data collected at the field station established in American 

 Samoa, and covers only the operations of the Samoa-based vessels. A considerable amount of 



Fig, 4 - Monliily mean sizes of albacore, by sex, landed at canner- 

 ies in American Samoa, September 1962 to December 1964, 



