Catch-effort records of two types have been used for 

 calculating ADIs: 1) records where walleye pollock were 

 the most abundant species in the catch which have been 

 defined as "pollock-majority-data" and 2) all-data rec- 

 ords. Based on records from five vessels class-gear types, 

 it was determined that ADIs resulting from the two 

 procedures were statistically the same in 80% of the 

 cases studied because of high proportion of pollock in 

 catches. However, in certain area-time cells where other 

 species formed a relatively high proportion of the catch, 

 the two procedures resulted in lower ADIs. Therefore, 

 use of data only from pollock-majority-data may cause 

 abundance to be overestimated while use of all-data 

 may cause it to be underestimated because some of the 

 effort may have been directed to another species. Thus, 

 ADIs calculated by either method may be biased 

 towards the high or low side and may not be directly 

 comparable from year to year. 



In an attempt to reduce such bias in ADIs, four area- 

 time cells were identified as potential index areas for 

 abundance computations. Three of these four cells 

 turned out to be good index areas for pollock. The ADI 

 procedure used thus resulted in an extension to the orig- 

 inal ADI procedure by Doi et al. (1972) to include: 1) 

 selection of vessel-gear categories that were most repre- 

 sentative of pollock fishing activities and 2) selection 

 of area-time cells that provided good indexing areas. 



Since then, the study has been updated to include 

 data analyses from 1964 to 1978. Trends in CPUE and 

 ADI show that from 1964 to the early 1970s, there was a 

 general increase in the abundance of pollock. This trend 

 was the result of increased pollock abundance and 

 fishing power of vessels. However, we cannot determine 

 the separate effect of these two factors. For 2-3 yr during 

 the early 1970s, abundance of pollock appeared to be at 

 peak levels. Beginning in 1972, both CPUE and ADI 



trends decreased but stabilized during 1975-78 at an 

 intermediate level when 1.1 million t of walleye pollock 

 were harvested annually. 



ACKNOWLEDGMENTS 



The International North Pacific Fisheries Com- 

 mission and the Fisheries Agency of Japan were instru- 

 mental in organizing the working group study which 

 resulted in this report. We wish to thank Yoshiya 

 Takahashi, Takashi Sasaki, Koya Mimura, Koji 

 Imamura, and Yasuho Tadokoro for their assistance and 

 advice during the workshop. 



LITERATURE CITED 



BAKKALA, R.. W. HIRSCHBERGER, and K. KING. 



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INTERNATIONAL NORTH PACIFIC FISHERIES COMMISSION. 



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