DISTRIBUTION OF THE YELLOWFIN IN SPACE 



The aspect of yellowfin distribution in space that bears 

 on the problenn of sampling variability is the presence or 

 absence of aggregation or schooling, for this affects the vari- 

 ability and determines the type of statistical distribution that 

 fits the catches. There is no direct evidence on the social 

 habits of yellowfin when they swim at the depths fished by the 

 longline (200 to 600 feet according to Murphy and Shomura 1953), 

 but they are known to form relatively compact schools at the 

 surface. Our first approach to the problem of schooling or non- 

 schooling involves examination of the location of hooked fish along 

 the line to ascertain whether the catch is randomly distributed or 

 whether it is grouped. The second approach is to compare the 

 relative variability between yellowfin and black marlin catches. 

 This comparison depends on the probability that marlin are not 

 schooled when they swim at subsurface levels because they 

 are generally seen singly at the surface (Nakamura 1949). 



Determination of schooling or non-schooling of yellowfin 

 by analysis of the distribution of the catches along the line is 

 analogous to a study of disease in plants that are growing in a row. 

 If the diseased plants are scattered at random the interpretation 

 would be that there is no evidence of contagion fSwed and Eisenhart 

 1943)e Similarly, if the tuna catch is randomly distributed there is 

 no evidence of schooling. An analysis of sequences (Mood 1950) is 

 appropriate to ascertain whether the distribution of hooked yellow- 

 fin is random. This involved determining from the total number of 

 hooks and the total catch of yellowfin the most probable number of 

 runs of hooks alike with respect to their bearing or not bearing 

 fish.—' If the tuna are schooled, there should be more instances 



3/ A run is defined as consisting of any nvunber of consecutive hooks 

 uniform with respect to occupancy or non-occupancy by fish and 

 boujided at both extremes by changes in this respect. Thus the 

 minimum possible number of runs in a longline set, which is one, 

 would be achieved either by having a fish on every hook, or by 

 having no catch at all. Conversely, the maximum possible nunnber 

 of runs would result from having a fish caught on every alternate 

 hook. In this case the total number of runs would equal the number 

 of hooks in the set, and each of the runs would comprise a single 

 hook. 



