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Fishery Bulletin 91(2). 1993 



Indices of apparent abundance 



Abundance index levels in tons/block area flight (17 

 BAF) were calculated for the total area by species for 

 day plus night observations for the years 1962-90 

 (Table 4). From the total area index, the general trend 

 of species abundance can be obtained. However, an 

 index designed to better represent abundance change 

 of each species is needed; therefore, a second set of 

 abundance index values was calculated using only data 

 from a core area of abundance as determined for each 

 species by day or night, depending upon which period 

 best represented the abundance of the species (Squire 

 1972). With the exception of data from one aerial spot- 

 ter pilot (computer file 26), all data collected during 

 1962-90 was used in this analysis. 



