FISHERY BULLETIN: VOL. 82, NO. 1 



Maturity Stage Versus Diet 



Information on maturity was gathered in conjunc- 

 tion with food data for 759 adult silver hake (Table 

 10). Gonads were classified as 1) resting - gonad 

 small in size and relatively translucent, 2) developing 

 - gonad enlarged and either cream (males) or yellow- 

 orange (females) colored, 3) ripe - gonad fills most of 

 gut cavity, reproductive material either runs freely 

 from an incision in the gonad or is extruded with pres- 

 sure on abdomen of fish, 4) spent - gonad is flaccid, 

 hemorrhaging is often evident. 



depth range (0.1 g). The quantity of food found in 

 stomachs of large fish is variable; it steadily de- 

 creases between the 27-37 m and 74-110 m depth 

 ranges; increases at the 111-146 m range; and from 

 1 1 1-146 m to 257-293 m continues to decrease (Ta- 

 ble 12). Overall, the trend is for fish sampled at 

 deeper depths to have less food, on the average, in 

 their stomachs. It should be mentioned here that 

 silver hake are known to regurgitate part or all of their 

 stomach contents when they are retrieved from deep 

 water depths (pers. obs.). Although fish which show 

 obvious signs of regurtitation (e.g., everted stomach) 



TABLE 10. — Relationship between the adjusted stomach content weight and 

 maturity stage of silver hake. Fish were caught on spring and autumn bottom 

 trawl survey cruises conducted in the Northwest Atlantic from 1973 to 1976. 



Stomach content 

 data 



Maturity stage Resting 

 Ad], weight (g): 826 



Developing 

 1.004 



Ripe 

 122 



Spent 

 1 292 



No. of fish examined 

 Mean fish FL (cm) 

 Length range (cm) 



379 



286 



24-35 



297 



30.6 



24-35 



29 



31 3 

 27-34 



54 



31.2 



25-35 



No particular prey type is found in the stomachs of 

 fish in specific maturity stages; all mature silver hake 

 eat mostly fish. However, the stomachs of spawning 

 (ripe) silver hake contain an average of about nine 

 times less food than the stomachs of fish otherwise 

 classified (Table 10). During pre- and postspawning 

 periods, stomachs contain the largest quantities of 

 food (1.0 and 1.3 g, respectively). 



Influence of Depth 



Analysis of samples from silver hake caught at dif- 

 ferent bottom water depth ranges (27->365 m) 

 revealed that the average length of fish, food type 

 consumed, and quantity of food in the stomachs, 

 varies with depth (Table 1 1). The majority (69.47c) of 

 silver hake were caught at depths between 38 and 

 110 m. Considering only the depth ranges where 

 more than 50 fish were sampled (i.e., 27-220 m, and 

 representing 95.6% of all silver hake collected) the 

 mean FL offish increases with an increase in depth. 

 Also, the percentage weight of euphausiids and squid 

 in the stomachs tends to increase at deeper bottom 

 depths, while the percentage weight offish in the diet 

 shows a corresponding decrease. The adjusted mean 

 stomach content data for both small and large fish are 

 given in Table 12. The data are from only those depth 

 ranges from which more than 20 fish (within a size 

 group) were collected. The adjusted stomach content 

 weight of small silver hake steadily decreases from 

 the 27-37 m depth range (0.3 g) to the 111-146 m 



are not sampled on survey cruises, some fish may 

 regurgitate and not be discernable from those which 

 did not, This phenomenon, in part (other factors such 

 as the decrease in abundance of typical prey of silver 

 hake with an increase in depth or decrease in bottom 

 water temperature may also be important in this 

 regard, see Williams and Wigley 1977) could explain 

 the decrease noted in stomach content weights with 

 an increase in water depth. 



DISCUSSION 



The diet of silver hake consists almost exclusively of 

 a combination of fish, crustaceans, and squid. The 

 relative importance of each particular prey group as a 

 food of silver hake is, for the most part, dependent on 

 the size of the predator and/or the availability of the 

 prey (Bigelow and Schroeder 1953; Jensen and Fritz 

 1960; Fritz 1962; Dexter 1969; Vinogradov 1972). 



The composition of the diet of male and female 

 silver hake is known to differ (Vinogradov 1972; Bow- 

 man 1975). The present investigation confirms 

 earlier reports that females feed predominantly on 

 fish and that males eat mostly crustaceans. In addi- 

 tion, it has been established that the stomachs of 

 females contain larger quantities of food than the 

 amounts in the stomachs of males of similar size. Since 

 the rate of growth in fishes is directly related to their 

 dietary intake, it is not surprising that females grow 

 faster than males (Schaefer 1960). 



Bowman and Bowman (1980) studied diurnal varia- 



32 



