Area-time cell III 



Area-time cell IV 



MBLs 32 and 33, April-July, 

 which represent the transitional 

 area (between spawning and 

 feeding grounds) during a transi- 

 tional period (between spawning 

 and feeding periods). 

 MBLs 43 and 44, June-Septem- 

 ber, which represents the north- 

 em feeding area during a feeding 

 period. 



Each area-time cell was selected to delineate a unique 

 phase of the distribution of the pollock population during 

 the year. From catch distribution patterns, we also deter- 

 mined that these phases of distribution were usually 

 repeated during the same area-time cell each year, there- 

 by providing comparability of ADIs from year to year. 



After the selection of these four area-time cells, ADIs 

 were computed for all vessel-gear categories except Type 

 2, which was already considered in Type 1. The computa- 

 tions were made using all-data as opposed to pollock- 

 majority-data within each cell because their results were 

 not expected to be significantly different. The equation 

 used to determine these ADIs was: 



ADI^ = (""2 (A,^ X 0^))/(""2A^) 



where a = 1,2,3,4 index area-time cells 

 g = 1,2,3,4 vessel-gear types 

 i = 1,2, . . . n statistical block number 

 riu = number of statistical blocks selected for 



computation in index area-time cell a 

 O^g = catch per unit effort (metric tons per hour 



trawled) by gear-vessel type g in statistical 



block i within index area-time cell a 

 A„j = area (km-) covered by vessel-gear type g 



which is made up of statistical blocks i 



within area-time cell a. 



(Table 9). Most of the decline occurred between 1973 and 

 1974, and from 1974 to 1976 relative abundance remained 

 fairly stable. 



TRENDS IN WALLEYE POLLOCK 

 ABUNDANCE 



Since we analyzed the 1964-76 data base at the 

 working group meeting in 1977, we have updated the 

 analyses on annual CPUE and ADI trends through 1978 

 as shown in Figure 3. They are trends of pair trawl data 

 from the surimi mothership fishery. From 1964 to the 

 early 1970s, there was a general increase in the CPUE 

 and ADI trends which resulted from increased pollock 

 abundance and fishing power of vessels. Catch composi- 

 tion and trends (Forrester et al. 1978) showed that pol- 

 lock became increasingly abundant as the fishery pro- 

 gressed in the 1960s. At the same time, there must have 

 been considerable learning experiences by fishermen 

 which contributed to higher CPUEs as noted by Lx)w 

 (1974). Technological changes in the fishing fleet also 

 took place, which no doubt increased the size and overall 

 efficiency of fishing vessels. Effects of these physical 

 changes on CPUE and ADI trends were probably held 

 rather constant by selecting data from our five standard 

 vessel class categories for computations. However, 

 we cannot separate the effect of increased fishing pow- 

 er of vessels from the effect of increased pollock abun- 

 dance in CPUE and ADI trends from 1964 to the early 

 1970s. 



For 2-3 yr during the early 1970s, abundance of pollock 

 appeared to be at peak levels. By this time most of the 

 technological changes and human learning factors that 

 contributed to increased fishing power have probably 

 stablized. Beginning in 1972, both CPUE and ADI trends 

 decreased but stabilized during 1975-78 at an intermedi- 

 ate level when 1.1 million t of pollock were harvested an- 

 nually. 



The results shown in Table 7 are ADIs calculated by 

 the above equation from monthly data by vessel-gear 

 type within each cell. A summarization of these monthly 

 ADIs by cell and gear type is presented in Table 8. In this 

 table, ADIs were weighted by the magnitude of catches 

 and then expressed in percentages relative to 1976 pair 

 trawl ADIs. 



In the interpretation of ADI trends within area-time 

 cells we also considered changes to the accustomed fish- 

 ing pattern due to factors such as fishing regulations. 

 Area-time cell I probably would not provide a good in- 

 dicator of pollock abundance for 1973-76 because that 

 cell was partially closed to trawling during some years 

 (INPFC 1979). Time-area closures have not been a factor 

 in the other three cells (U-IV) and fishing patterns did 

 not change significantly during 1973-76. Thus, ADIs were 

 better indicators of stock abundance in these latter three 

 cells than in cell I. 



The trend in ADIs shows that relative pollock abun- 

 dance declined from 1973 or 1974 to 1976 in all cells 



SUMMARY 



The data base and an average density index (ADI) 

 procedure for assessing abundance of walleye pollock in 

 the eastern Bering Sea were evaluated. This data base 

 was made up of daily catch-effort records of individual 

 fishing vessels in the Japanese groundfish fishery. For 

 the period 1964 through October 1972, the data base 

 consisted of a third of the total daily catch-effort rec- 

 ords. Thereafter, all daily records were included. Based 

 on pair trawl data from the 120-219 gross registered ton 

 class of vessels in the surimi mothership fishery, it was 

 determined that one-third of the records provided a 

 statistically representative sample of the entire data 

 base. It was further determined that monthly sum- 

 maries of daily catch-effort records that have been sub- 

 mitted by Japan to INPFC and used by U.S. scientists 

 for assessing abundance of walleye pollock were not sig- 

 nificantly different from daily records used by the Fish- 

 eries Agency of Japan in their assessments. 



