FOOD OF SILVER HAKE, MERLUCCIUS BILINEARIS 



Ray E. Bowman 1 



ABSTRACT 



Stomach contents of 2,622 silver hake collected in the Northwest Atlantic have been analyzed. Fish were 

 collected on bottom trawl surveys conducted from 1973 to 1976. The mean fish fork length (FL) was 20 cm 

 and the average stomach content weight was 1.5 g. Silver hake <20 cm FL prey mostly on amphipods, 

 decapod shrimp, and euphausiids. Fish 20 cm FL and longer take increasing proportions of fish and squid as 

 part of their diet. Stomach contents of male and female fish of similar size indicate that females eat larger 

 quantities of food (particularly more fish) than the males. The females are also, on the average, longer than 

 the males. Silver hake feed primarily at night. Feeding begins near dusk and continues until just after mid- 

 night. In the spring a second feeding period seems to occur near noon. Silver hake feed intensively during 

 spring. Their stomachs contain almost twice as much food in spring as they do in autumn. Significant dif- 

 ferences were noted in the intensity of feeding between areas. Stomachs of fish, caught in the Middle Atlantic, 

 contain the largest quantities of food. The species of prey taken by silver hake are highly variable and likely 

 reflect prey availability during different years and seasons in various areas. When silver hake spawn, their 

 dietary intake is reduced. The diet of fish taken in deep water (> 150 m) is mostly euphausiids and squid, and 

 the quantity of food found in their stomachs is less than that in stomachs taken from fish collected at depths 

 <150m. 



Silver hake, Merluccius bilinearis (Mitchill 1814), is a 

 Northwest Atlantic gadiform fish whose range ex- 

 tends from continental shelf waters off South Caro- 

 lina to the Newfoundland Banks. It is most abundant in 

 offshore waters extending from New York to Cape 

 Sable, Nova Scotia (Bigelow and Schroeder 1953). 



Previous investigations have shown that large silver 

 hake eat mostly fish and/or squid, while smaller silver 

 hake feed on euphausiids, amphipods, and decapod 

 shrimp. Among the first to report these findings were 

 Nichols and Breder (1927), who noted 75 herring 

 about 7 cm long in the stomach of a 59 cm fish. 

 Bigelow and Schroeder (1953) reported that silver 

 hake are extremely voracious and will prey on smaller 

 silver hake or any other of the schooling fishes such as 

 young herring, mackerel, menhaden, alewives, or silver- 

 sides. Evaluation of other studies on the diet of silver 

 hake caught in various areas and during different 

 years establishes that the prey of silver hake is very 

 predictable in that it is usually comprised of a variety 

 of fish, squid, and crustaceans (Jensen and Fritz 

 1960; Schaefer 1960; Vinogradov 1972; Noskov and 

 Vinogradov 1977; Bowman and Langton 1978; Lang- 

 ton and Bowman 1980). Investigations by Swan and 

 Clay (1979), Edwards and Bowman (1979), and Bow- 

 man and Bowman (1980) have shown that silver hake 

 feed mostly at night. 



Until recently the potential impact of silver hake on 



'Northeast Fisheries Center Woods Hole Laboratory, National 

 Marine Fisheries Service, NOAA, Woods Hole, MA 02543. 



Manuscript accepted July 1983. 



FISHERY BULLETIN: VOL. 82, NO. 1, 1984. 



the Northwest Atlantic ecosystem had not been de- 

 termined. Edwards and Bowman (1979) estimated 

 the annual consumption of the principal predators in 

 the Northwest Atlantic. They concluded that silver 

 hake alone could potentially consume almost 10% of 

 the standing crop of all fish within the study area an- 

 nually, the bulk of which would be small or juvenile 

 fish. They suggested that silver hake, more than any 

 other species, plays the principal predatory role in 

 regulating the Northwest Atlantic ecosystem. The 

 purpose of this report is to document the quantities 

 and types of food eaten by silver hake during the 

 years 1973-76, and further, to identify feeding trends 

 which may be of consequence when attempting to 

 precisely determine silver hake's impact on other fish 

 populations. 



METHODS AND MATERIALS 



A total of 325 samples from 2,622 silver hake 

 stomachs was collected during eight MARMAP (Mar- 

 ine Resources Monitoring, Assessment, and Predic- 

 tion) bottom trawl survey cruises conducted by the 

 National Marine Fisheries Service during spring and 

 fall 1973-76 (Table 1). The cruise periods were as 

 follows: 16 March-15 May 1973; 26 September-20 

 November 1973; 12 March-4 May 1974; 20 Sep- 

 tember-14 November 1974; 4 March-12 May 1975; 

 15 October- 18 November 1975; 4 March-8 May 

 1976; 20 October-23 November 1976. On spring 

 cruises a two-seam modified Yankee No. 4 1 trawl was 



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