FOOD HABITS OF PACIFIC WHITING, 



MERLUCCIUS PRODUCTUS, OFF 



THE WEST COAST OF NORTH AMERICA, 



1967 AND 1980 



The Pacific whiting, Merluccius productus, forms a 

 major groundfish resource off the west coast of North 

 America. According to Nelson and Larkins (1970) it 

 is "one of the most abundant species of fish in the 

 northeastern Pacific Ocean." Fishing effort on the 

 Pacific whiting stock has increased dramatically 

 since 1965 when it became the target of the United 

 States and Soviet fishermen (Grinols and Tillman 

 1970). The stock is now the basis of a large U.S. joint- 

 venture and domestic fishery. Management of this 

 stock requires more detailed information on the 

 major prey of Pacific whiting throughout its 

 distribution. 



Previous studies have shown that Pacific whiting 

 feed primarily on euphausiids, but at certain times 

 commercially important fish or pandalid shrimp may 

 constitute an important item in the diet (Gotshall 

 1969a, b; Alton and Nelson 1970; Outram and 

 Haegele 1972). Indirect evidence of nocturnal feed- 

 ing by Pacific whiting has also been presented by 

 Alton and Nelson (1970) and by Outram and Haegele 

 (1972). Although these studies contain useful 

 baseline information, they are not complete enough 

 to describe quantitatively the predatory interactions 

 of Pacific whiting, with the exception of Gotshall' s 

 ( 1 969a, b) study which focused only on the impact of 

 whiting predation on the commercially important 

 pink shrimp, Pandalus jordani. 



The objective of the present study is to provide a 

 quantitative account of the predatory patterns of 

 Pacific whiting by identifying their major prey items, 

 determining whether size-selective predation occurs, 

 examining diel feeding behavior, and calculating 

 daily ration. 



Collection and Processing of Samples 



Stomachs of adult Pacific whiting were collected in 

 1967 off the Oregon and Washington coasts 

 (Livingston and Alton 1982) and in 1980 off Oregon, 

 Washington, and Vancouver Island (Fig. 1). Also, 

 samples of juvenile Pacific whiting taken off the 

 California coast in the fall of 1980 were saved for 

 stomach analysis (Table 1). Samples were obtained 

 during resource assessment surveys using either bot- 

 tom or midwater trawls. Only vessels operating dur- 

 ing daylight hours used bottom trawls to survey 

 whiting which were mostly on the sea bottom. Mid- 

 water trawls were used on those vessels with both day 



and night operations so that the net could be set at 

 depths of greatest whiting concentration. Stomach 

 samples were taken opportunistically at standard 

 resource assessment stations. In 1967, most stations 

 were at bottom depths of < 100 m, while in 1980 bot- 

 tom depths ranged from 77 to 298 m. Stomachs were 

 taken randomly from the entire catch in 1967, but 

 were stratified in 1980 by 10 cm whiting length 

 groups. 

 A 15-h time series of stomach samples was taken in 

 1967 at a station off the Washington coast to detect 



50° 00'N 



 - 46° 00'N 



42° 00'N 



125° 30'W 



123° 30'W 



FIGURE L— Sampling locations for Pacific whiting, Merluccius pro- 

 ductus, in 1967 (+) and 1980 (•) in relation to the 100 m depth con- 

 tour (---). 



FISHERY BULLETIN: VOL. 81, NO. 3, 1983. 



629 



