294 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



which appears to be perpendicular rather than 

 parallel to the barrier formed by the islands. The 

 relative speed with which schools travel, which 

 may reach 15 knots (Eoyce and Otsu, p. 18), may 

 be such that a period of 2 weeks is too long to dis- 

 cern a migi-atoiy pattern within an area as small 

 as that encompassed by the Hawaiian skipjack 

 fishery. 



Small Skipjack 



Examination of the numbers of small skipjack 

 caught and the corresponding catch per unit-of- 

 effort data revealed no discernible pattern of move- 

 ment within the fishery. Large skipjack are the 

 prime objective of the fishery and the smaller sizes 

 are usually taken as a second choice. The number 

 of small skipjack in the catch, therefore, tends to 

 be a function of the number of large fish available. 

 The relationships between the numbers of large 

 and small fish in the catch are discussed under the 

 section, Size Composition. 



OAHU SKIPJACK FISHERY, 1952 AND 1953 



STATISTICAL COMPARISONS 



The comparative statistics for 1952 and 1953 in 

 the Oahu region are summarized in table 7. In 

 almost every way, 1953 reflects the greater avail- 

 ability of skipjack than in the previous year, as 

 evidenced by (1) a mucli larger catch, (2) almost 

 half as much fishing effort, and (3) a larger catch 

 per unit of effort. The number of small skipjack 

 caught (4b) and pounds caught per unit of effort 

 (3b) are not markedly different between years, but 

 the catch of large fish, both in absolute numbers 

 (4a) and on a relative basis (3a), is considerably 

 gi-eater in 1953. Most of the differences between 

 the 2 years can be attributed to the abundance of 

 this size group in the fishery. 



Independently of size considerations, the num- 

 ber of fish taken per biweekly period in 1953 was 

 larger than the corresponding number in 1952 (5 

 and 6) . The relative abundance of large and small 

 skipjack in the 2 years is indicated by the nimiber 

 caught per unit of effort (7) wliicli is greater for 

 the small fish in 1952 and for the large fish in 

 1953. The importance of the abimdance of large 

 fish to the success of the fishery may be measured 

 by the comparative number of biweekly periods in 

 the various categories (8). 



Table 7. — Comparative statistics for the Oahu fishery, 

 1952 and 1953 



1. Total pounds caught 



(Percent of total for skipjack fishery). 



a. Large skipjack only 



b. Small skipjack only 



2. Total productive elTort _-_ 



a. Large skipjack, percent 



h. Small skipjack, percent 



3. Pounds caught per unit of effort, all 



usable catches 



a. Large skipjack only, ___ 



b. Small skipjack only 



4. Total number of flsh caught 



a. Large skipjack only 



b. Small skipjack only 



5. Average number caught per biweekly 



period 



6. Median number of skipjack caught in 



each year for the 26 biweekly periods. 



7. Number of fish caught per unit of 



effort _. 



a. Large skipjack only 



b. SmaU skipjack only 



8. Number of biweekly periods with — 



a. more than 300,000 pounds catch. 



b. more than SOO units Ashing ef- 



fort 



c. more than 400 pounds catch per 



unit of effort 



1953/1952 



3.09 



.92 



1.45 



1.30 

 1.16 



.97 

 1.30 

 2.67 



.87 



1.27 



1.43 



.88 

 1.11 



.87 



2.80 

 2.20 

 2.80 



RELATIONSHIPS BETWEEN CATCH STATISTICS 



The population indices derived from the catch 

 reports are the raw catch and the relative catch; 

 i.e., catch per unit of effort. Either index may be 

 in terms of weight or number of fish and may be 

 calculated for the entire catch or for limited cate- 

 gories. Since 1954, however, no information on 

 the number or size of fish in the catch has been in- 

 cluded in the catch report, so the only indices 

 which may be considered for recent years in the 

 fishery are the pounds caught and the catch per 

 unit of effort without respect to size categories. 



The biweekly statistics for pounds caught, catch 

 per unit of effort, and effort within the Oahu 

 region for 1952 and 1953 are plotted in figure 11. 

 Of particular interest here is the relation be- 

 tween the raw catch and the catch per unit of 

 effort, for if the two show essentially the same 

 variation, there is little or no advantage to be 

 gained in employing catch per unit of effort as tlie 

 index of apparent abundance. 



It is obvious from figure 11 that there is much 

 similarity in the fluctuations of all three indices; 

 each has a seasonal variation on which lesser fluc- 

 tuations are superimposed. Additionally, there is 

 a secular trend from 1952 to 1953. The catch 

 curve tends to change gradually and peak sharply, 

 while the effort curve changes rapidly at the start 

 and close of the season, with little trend during 

 midyear. 



