CONTENTS 



Introduction 1 



The walleye pollock fishery 1 



Data base 2 



Average density index 2 



Topics of analysis 2 



Examination for bias in the 1964-72 data base 3 



Variability studies on pair trawl data 4 



Comparison of ADIs from all-data versus pollock-majority-data 6 



Index area-time cells 7 



Trends in walleye pollock abundance 8 



Summary 8 



Acknowledgments 11 



Literature cited 11 



Figures 



1. Mapof the Bering Sea showing statistical grids used in the Japanese ground fish data base 3 



2. Four area-time cells used for calculating average density indices for walleye pollock in the eastern 

 Bering Sea 7 



3. Trends in catch per unit effort (CPUE) and average density index (ADI) for walleye pollock in the 

 eastern Bering Sea, 1964-78 10 



Tables 



1. Annua! catch of walleye pollock, in thousand metric tons, in the eastern Bering Sea, 1964-78 2 



2. Percentage of walleye pollock catches relative to total catches accounted for by major Japanese ves- 

 sel-gear categories in the eastern Bering Sea, 1973-76 3 



3. Statistics on variability studies on catch-effort data for pair trawlers in the 120-219 gross registered 

 ton class in the Japanese surimi (a minced fish product) mothership fishery of the eastern Bering 



Sea, 1964-76 4 



4. Statistics on variability studies on mean annual catch per unit effort (CPUE) of walleye pollock by 

 pair trawlers of the 120-219 gross registered ton class in the Japanese surimi (a minced fish product) 

 mothership fishery in the eastern Bering Sea, 1964-76 6 



5. Average density indices, in metric tons per hour trawled, for all-data versus walleye pollock- major- 

 ity-data by vessel-gear categories in the eastern Bering Sea, 1973-76 6 



6. Number of major statistical block months in which average density indices computed from all-data 

 versus walleye pollock-majority-data in the eastern Bering Sea were the same, differed by 0.1, or dif- 

 fered by more than 0.1 metric tons per hour trawled 6 



7. Comparison of average density indices, in metric tons per hour trawled, for walleye pwllock in the 

 eastern Bering Sea by area-time cells (see Figure 2 and text) and vessel-gear categories, 1973-76 .... 9 



8. Annual average density indices (ADIs; in metric tons per hour trawled) and relative ADIs (as percent- 

 age of 1976 ADI) for walleye pollock in the eastern Bering Sea by area-time cells (see Figure 2 and 



text) and vessel-gear categories, 1973-76 10 



9. Overall average density indices (ADIs; as percent of 1976 metric tons per hour trawled) for walleye 

 pollock in the eastern Bering Sea computed from ADIs in area-time cells which were weighted by 

 catches, 1973-76 10 



111 



