BOTSFORD ET AL.: CYCLIC COVARIATION IN CALIFORNIA FISHERIES 



T 



DO 



CD 

 CC I 



O u. O"- Ou-Ou- Oli- Ou- Oli- O 



a 



o 



o 



o 



o 



o 



o 



o 



z 



o 



z 



o 



z 



o 



z 



o 



z 



o 



O u- 



o 



CD 



O 



CO CD 



C >. 



■O CO 

 < LU 



cyclic while silver salmon is less so. The latter 

 may be due to the shorter time record for silver 

 salmon. First-differencing decreases the value of 

 the peak of negative correlation in king salmon to 

 an insignificant level but the pattern is pre- 

 served. 



Estimates of cross-correlation between crab 

 catch and catch of each salmon species appear 

 similar to the correlation between crab catch and 

 total salmon catch (Fig. 5). Again, the observed 

 characteristics seem to be stronger in the king 

 salmon rather than the silver salmon records. 

 First-differencing of the crab and salmon series 

 reduces correlation values so that the positive 

 correlation at a negative lag remains significant 

 for king salmon only (Table 1). 



i o 



o 

 < 



tr 



o 

 o 



00 

 00 



o 

 tr 

 o 



0.5 - 



0.0 - 



-0.5 - 



-1.0 



-15 



■10 



-5 



LAG (years) 



10 



15 



Figure 5.— An estimate of the cross-correlation function be- 

 tween northern California crab catch and king salmon and sil- 

 ver salmon for the years 1952-76. 



Central California Total Catch 



Because of differences between the central 

 California crab fishery (Fig. 6) and the northern 

 California crab fishery, comparison of charac- 

 teristics of covariation between salmon and crab 

 in northern California with that in central Cali- 

 fornia provides some basis for determining the 

 underlying cause of the covariation in northern 

 California. We can narrow the range of possible 

 causes by determining whether the covariation 

 under discussion here exists both before and 

 after the decline of the crab fishery in 1961. This 

 investigation is, however, somewhat hampered 

 by the extremely short time series that result 

 from bisecting these records. 



For the predecline period (1940-61), the auto- 



795 



