Ad jus t for aggregation habits » ■= If a series of samples taken at a 

 particular fishing port be 'compared as to size-composition, it is apparent 

 that among them there are samples that resemble each other sufficiently 

 to have come from the same population but differ enough from certain other 

 samples to indicets that the latter must have come from different popula- 

 tions o Since ths various samples come from different schools it appears 

 that certain groups of schools have a uniform pattern of size-composition 

 and, if so^ t'ney must have been associated for a significant period of time 

 during which their reaction pattern was the sane within;, but different be = 

 t"vveenj the groups of schools o This corresponds to views expressed by wT~Fo 

 Thomps on (1926 po 163)? "Catches of a certain type^ or 'runs" having cer- 

 tain characteristics, prevail for varying periods of time, and each of 

 these periods is a variable unit itselfo'* Our view differs only in sup- 

 posing that there may be simultaneous ocoxirrence of different types of 

 "'rvmSp'* -- a possibility doubtless appreciated by Thompson or one that 

 certainly would have been,, if the fishery of a given port had spread over 

 as large an area_„ then as nowo It will be convenient to refer to what we 

 have called ''groups of schools'* and what Thompson has called "runs" as 

 school -groups <, 



Obviously the population fished from a given port is not randomly 

 distributed as to si2,e<, Unless the period of time each school-group is 

 "available" to the fishery is either g (1) Random or (2) proportional to 

 the abundance of each school-groupj our sampling system, even though ^strati 

 fied" as to time, and even though weighted according to catch-per-boat 

 in the time strata, cannot faithfully represent the population of school 

 groups fished from that port during a fishing seasono 



The summation of such weighted samples would weight the sizes in 

 accordance with the frequency or length of time the school-groups domi- 

 nated by those si^.es were fished by the flee to Since the length of time 

 the school-group is present and available on a ground is more likely to 

 be associated with its reaction pattern and the fluctuations in oceano- 

 graphic conditions tlian with the relative numbers of fish represented 

 by each school-group, such weighting would represent largely availability 

 rather than abundanos of f isho 



At the present time (spring of 1942) means of distinguishing school- 

 groups are being developed » Methods of employing the school-group idea in 

 adjusting samples will have to await analysis of the occurrence and persis- 

 tence of school-groupE o It may lead to a method of weighting in school- 

 groups or of combining samples in certain manners or may merely serve as 

 back-ground information for appraising the validity of methods based on 

 other principles o Since methods are still uncertain the rectangle labeled 

 "'Adjust for aggregation habits'" has been related to the main line of pro- 

 cedure by a broken lineo 



Compute seasonal weights o = Apart from the departure from random 

 distribution of s'cEool"^roups within short periods of time, there is an 

 even greater difference between the fall and winter populations in Califor- 

 nia, especially in the seasons prior to 1938-39o The fall fish are pre- 

 dominantly young adultSj, 3 to 5 or 6 years of age 5 the winter fish, old 



