On ths other handj, it will probably be safe to rep;ard competition 

 betv/een gear as negiigiblej, a point of view that is tenable if cooperation 

 is the effective result of increasing the nianber of boats and also if 

 the schools of sardines are so widely distributed that instances are 

 relatively rare wherein a boat is prevented from making a catch by the 

 pre~emption of space by another boat»3/ We do not consider in the cate- 

 gory of competition the situation where the probability of catching 

 a school of sardines has been reduced by the number of schools taken 

 out of that locality previcuslyo This is a phenomenon of reduction of 

 the stock by catch mortalityo It is taken into account by appreciat- 

 ing the distinction between average abundance and initial abundance 

 in any particular period of timeo (See Ricker 1940 po 45) o 



RELIABILITY 



Having computed one set of values on natural mortality, catch mor= 

 tality, and recruitment <, one gains a general idea of the magnitude of 

 eachj, but the result cannot by any means be considered a determination. 

 The various computations and adjustments have contributed errors <> Also 

 the original data had variability which perhaps was increased rather 

 than diminished by the subsequent treatmento The mathematical result, 

 therefore, has a probability of differing from the true value by an 

 amount which cannot be known from one set of values alone. 



In a series of sets of values, however^, from which one might com- 

 pute a regression,, savj, of catch mortality on fishing intensity, the 

 spread of values around the regression line would give a measure of 

 variability and one could be said to have really made a determination 

 if that spread is small in relation to the magnitude of the observed 

 change in catch mortalityo 



While this would appraise the random error, it might not detect 

 even a large amount of error consistently above or below the true value 

 for the entire series o Such an error might easily be introduced by 

 simplifying assumptions or by failure to take into account certain sources 

 of consistent bias or selsctiono It could be detected only by comput- 

 ing the same statistics by an entirely different method and from a dis- 

 tinct source of data. The tagging technique affords such a method and 

 'atilizes a considerably different set of original data, although, to 

 the extent that the same commercial catch is involved, errors in fisher= 

 men's sampling majr be in the same direction as in the other methodo 



3/ Persons familiar with the fishery might say that such instances are 

 common rather than r».r6o It is true that there often seems to be a race 

 between two or more boats to set their seines around the same school. 

 This may actually take place at times, but more often a boat, preparing 

 to make a set, betrays its intention by its actions, and so leads other 

 boats to come to the same spoto They do sOj, not necessarily in the hope 

 of beating the original boat to the school it has sighted^, but in the 

 hope, often realised, that other schools are to be found in the same vicin- 

 ityo All such instances should be classified as cooperational rather than 

 competitive. TTnder the latter category, there should be included only the 

 cases where two boats inde pendently locate and try to set upon the same 

 school. Such cases oi'' true competition probably are not more numerous 

 than would serve to offset the contrary element of cooperation. 



