though it may appear from the values of effi- 

 ciency factors in table 11 that Class 2 vessels 

 always have better results than Class 1 vessels, 

 the data indicate that, on the average, the 

 offshore catches of Class 1 vessels are likely 

 to be larger than those of Class 2 vessels fish- 

 ing in inshore waters. 



Catch per Standard Effective Trip 



The efficiency factors, given in table 11, 

 were used in calculating the standard unit of 

 effort. For example, in 1952 there were 855 

 effective trips by Class 1 vessels and 692 by 

 Class 2 vessels. The standard effective trip 

 is the sum of the products of the mean effi- 

 ciency factor and total number of effective trips 

 of the size classes: 



0.74(855) + 1.00(692) = 1,325 standard 

 effective trips. The catch per standard effective 

 trip (Y/f ; the notation f refers to fishing ef- 

 fort expressed in standard effective trips) is 

 found by dividing the sample catch by the 

 standard effective trips: 



6,277,046 



= 4,737 pounds per standard ef- 



1,325 



fective trip ; and the fishing intensity is ob- 

 tained from the total catch and Y/f: 



7,291,851 



1,539 standard effective trips. 



4,737 



The Y/f reflects only apparent abundance 

 based on the trips on which fish were caught. 

 The total catch of skipjack tuna in pounds, 

 Y/f, and relative effective fishing intensity per 

 Class 2 trip are presented in table 13 and 

 the index curves are illustrated in figure 8. 



Table 13. — Tolal landings of skipjack tuna in Hawaii, catch 

 per standard effective trip, and relative effective fishing in- 

 tensity, 1952-62 



19S2 1953 1954 1955 195G 1957 1958 1959 1960 1961 1962 

 YEAR 



Figure S. — Total catch, catch per standard effective 

 trip, and the relative effective fishing intensity for 

 skipjack tuna in Hawaii, 1952-62. 



The curve for Y/f was at 4,737 pounds in 1952, 

 rose in 1953 and again in 1954 to reach a 

 peak of 6,983 pounds, then dropped to about 

 the 1952 level in 1955. Another peak in 1956 

 was followed by a decline to its lowest level in 

 1957. The Y/f reached another peak in 1959, 

 surpassing that of 1954. The Y/f had no trend; 

 rather, the values varied around an average of 

 about 5,700 pounds per standard or Class 2 

 trip. The relative effective fishing intensity 

 exhibited a slight decreasing trend from about 

 1953 to 1958 and leveled oflf at about 1,600 

 standard trips in 1959-62. 



INTERRELATION OF TOTAL CATCH, FISHING 

 INTENSITY, AND APPARENT ABUNDANCE 



The catch per standard effective trip (Y/f) 

 and the total catch fluctuated in a similar 

 fashion in 1952-62 (r = 0.851; df = 9; p 

 <0.001). For the 11-year period, then, the 

 total catch may be used as an index of apparent 

 abundance, but it should by no means be con- 

 sidered an appropriate index in other years. 

 The situation may change in other years, be- 

 cause of the sensitivity of the total landings 

 to various influences such as weather, sea con- 

 ditions, the amount of effort expended, and the 

 market for skipjack tuna. 



The Y/f and the relative effective fishing 



U.S. FISH AND WILDLIFE SERVICE 



193 



