cause the data for the earlier years — particularly 

 1954 and 1955 — are not strictly comparable with 

 those of later years. As we already stated, fishing 

 in the early stages of the fishei-y was aimed pri- 

 marily at taking yellowfin tuna rather than alba- 

 core; thus, the catch of albacore per fishing trip 

 was relatively small as compared with later years. 

 It is clear, however, that the annual landings of 

 albacore have tended to increase with increasing 

 fishing effort. Generally, it would be expected that 

 the total catch would increase as fishing effort in- 

 creases, until a point of maximum yield (not nec- 

 essarily the point of optimum yield) is reached. 

 After this point is reached, the catch would gen- 

 erally decrease despite fiirther increase in effort. 

 From the data presented in figure 10, it does not 

 seem that the point of maximum yield of albacore 

 has yet been reached in the American Samoa-based 

 fishery. The extent of the growth potential, how- 

 ever, is a subject of another study — one which will 

 require the analysis of all available South Pacific 

 data, not merely those collected from the American 

 Samoa-based vessels. 



RELATION BETWEEN CATCH PER UNIT OF 

 EFFORT AND EFFORT 



The annual average catch per trip shows an 

 apparent increase with increase in fishing eft'ort 

 (fig. 11). The catch per trip in 1963, 1964, and 

 1965, however, failed to increase at the rate seen 

 before 1962. The data are far too few, however, to 

 be conclusive. 



VALIDITY OF CATCH PER 100 HOOKS AS 

 MEASURE OF APPARENT ABUNDANCE 



Under the assumption that the catch per 100 

 hooks is the better measure of apparent abundance 

 of a species taken by the longline method, such 

 data have been collected continuously since 1963. 

 Estimates of abundance of fish based on catch per 

 day or catch per trip might be influenced by the 

 size of tlie fishing vessel. Although there seems 

 to be no reason for believing that catch per 100 

 hooks would also be afi'ected by vessel size, this 

 question was examined inasmucli as it is con- 

 ceivable that the larger vessels may be more at- 

 tractive to fishennen than smaller vessels and, 



2 20 



150 200 250 300 350 

 NUMBER OF FISHING TRIPS 



400 450 500 



Figure 11. — Relation between average catch of albacore 

 per trip and total flsbins trips, of American Samoa- 

 based Te.ssels, 19.J4-C.J. 



thus, may have a better choice of fishermen and 

 fishing masters who would have the skill to catch 

 more fish. If so, some efficiency factors would need 

 to be incorporated in tlie use of catch per 100 

 hooks to adjust for differences among vessels. 



A tabulation of albacore catch per 100 hooks by 

 vessel sizes (gross tonnage) revealed a tendency 

 for larger vessels to obtain higher catch rates than 

 smaller vessels (table 2). In 1963, the smallest ves- 

 sels (under 80 gross tons) averaged 4.6 albacore 

 per 100 hooks, but catches trended upward to 5.8 

 albacore per 100 hooks for the vessels of 121 to 

 140 tons. Tlie average catch rate was lower (5.1) 

 for the largest vessels (those over 141 gross tons). 

 In 1964, the trend, if any existed, was less obvious. 

 To examine this apparent relation between vessel 

 size and catch rate, the catch rate for each trip 

 was plotted against vessel size for each of the 24 

 months. The scatter of points about the regression 

 lines, fitted by the least squares method, was con- 

 siderable; only the data for June and November 

 1963 and September 1964 showed statistically sig- 

 nificant regressions (P<0.01). The data for these 

 3 months, however, were very heavily influenced 

 by the results of a dispi'ojjortionately small num- 

 ber of both the smallest and largest vessels in the 

 fleet. 



54 



U.S. FISH AND WILDLIFE SERVICE 



