HOBSON and CHESS: TROPHIC RELATIONS OF THE BLUE ROCKFISH 



42°N 



41°N 



40°N 



39°N 



38°N 



37"N 



125°W 124°W 123°W 122°W 121°W 



Figure 2.— The coast of northern California. 



eral state of the weather, including wind direction 

 and estimated velocity. In this paper (except in 

 Figures 4 and 9, as noted below) we consider winds 

 from between northwest and northeast to be 

 "northerly", and from between SW and SE to be 

 "southerly". We also noted sea conditions and 

 recorded sea-surface temperatures. More precise 

 wind data became available after May 1980, when 

 a NOAA weather station was established at Mendo- 

 cino. During the same month, we placed recording 

 thermographs at depths of 6 and 20 m in the study 

 area, and although the deeper site was abandoned 

 after 1981 in favor of replicating the record with 

 two instruments at the shallower site, these have 

 given us a continuous record of water temperatures 

 from then until the present (Spring of 1988). Based 

 on these observations and in situ visual assessments 



of the plankton and water characteristics, usually 

 we could tell whether upwelling or downwelling 

 predominated during a sampling session even 

 though most of the time conditions were to some 

 extent mixed. 



Diet and Occurrences of Food 



To relate the diet of S. mystinus to foods present 

 at the time of feeding, we took concurrent samples 

 of gut contents and plankton, as well as some selec- 

 tive samples of the benthos. Complications from 

 normal diel variability were reduced by taking all 

 samples between the hours of 1100 and 1300. The 

 sampling schedule was strongly influenced by the 

 weather, as much of the time work was prevented 

 by high seas and/or long-period swells and result- 



717 



