Hannah and Jones: Fishery-induced population changes in Pandalus jordani 



47 



— 24.0 



E 



E 



22 



a 



< 



Q. 

 < 



< 



O 



< 



20 0- 



18.0- 



16 



120 



10 



24.0 



AREA 19 



1965-76 BROODS 

 1977-86 BROODS 



1   I  

 15 



20 25 



AGE IN MONTHS 



30 



35 



AREA 26 



20 25 



AGE IN MONTHS 



35 



35 



AGE IN MONTHS 



_ 24.0 



E 

 E 



22.0 



X 



t- 



O 



Z 20.0 



ui 



16.0 



< 

 a 

 < 

 K 

 < 

 O 



z 14.0 



< 



ui 



5 12.0 



AREA 21 



-G — 1 965-76 BROODS 

 1 977-86 BROODS 



-i— i— i— i— i— i— i— r- 



10 



20 25 



AGE IN MONTHS 



30 



35 



Figure 7 



Mean length at age for the 1965-76 and 1977-86 broods of pink shrimp from Oregon statistical areas 19, 21, 22, and 26. 



_ 8000 



YEAR OF CATCH 



Figure 8 



Age composition by number of the catch of pink shrimp from 

 statistical areas 18-28 for the years 1966-88. 



older shrimp, and a sexually balanced breeding popula- 

 tion has been maintained (Fig. 10). 



Discussion 



Our analysis supports a conclusion that pink shrimp are 

 exhibiting density-dependent growth. The transition to 

 larger mean size at age between 1978 and 1979 coin- 

 cides nearly exactly with the large drop in fishery 

 CPUE, and the shift in age composition of the catch 

 toward younger ages (Figs. 6, 8). This is probably due 

 to the intensive development of the fishery during the 

 mid 1970s (Fig. 11). The fishery continued to intensify 

 after 1978, with subsequent effort levels falling to 

 pre-1977 levels only in the years 1983-1985 (Fig. 12). 

 The persistence of reduced CPUE and reduced mean 

 age at capture are classic results of an intense size- 

 selective harvest causing reduced levels of population 

 biomass. 



