BOWMAN: FOOD OF SILVER HAKE 



<0.1%), Polychaeta, and the "Miscallaneous" 

 category, which consisted of small amounts (<0.1%) 

 of Echinodermata, Chaetognatha, unrecognizable 

 digested matter, and sand. 



The percentage weights of various prey of silver 

 hake within specified length groups are listed in Ta- 

 ble 3. Silver hake <20 cm FL eat mostly crustaceans 

 (>80% on the average), whereas the food of in- 

 dividuals >20 cm FL is mostly fish and squid 

 (average over 50%). Stomachs of silver hake 3-5 cm 

 FL contain the largest percentages of smaller crusta- 

 cean forms, such as amphipods and copepods. 

 Decapods, euphausiids, and mysids, which are 

 generally larger organisms (see Gosner 1971), make 

 up the largest percentage of the diet of fish 6-20 

 cmFL. 



Diet Differences Between Males and 

 Females 



The diet of male and female silver hake differs in 

 both quality and quantity of food (Table 4). The 

 stomachs of males have the largest percentage of 

 crustaceans, while those of females have the largest 

 percentage offish and squid. The mean stomach con- 

 tent weight of the males is only about one-fifth that of 

 the females. Males also occur less frequently in the 

 samples (42% of the fish collected were males) and 

 are generally smaller than the females (mean FL 

 males, 28.4 cm; females, 32.1 cm). Since female fish 

 are, on the average, longer than the males, the dif- 

 ferences noted above had to be dealt with in con- 

 siderably more detail. 



A comparison of the data in Tables 5 (food of males) 

 and 6 (food of females) indicates that males and 

 females within the same size groupings consume dif- 

 ferent types and amounts of food. The same dietary 

 patterns noted for male and female fish in the preced- 

 ing paragraph can be seen within most of the in- 

 dividual length groups in these two tables (e.g., when 

 males and females within the same size group are 

 compared, the stomachs of the females contain larger 

 quantities of food and higher percentages offish and 

 squid). The number of males sampled generally ex- 

 ceeds the number of females for length groups <30 

 cm, while females dominate the length groups >30 

 cm. 



A subset of the data were analyzed separately using 

 only fish lengths for which 20 or more individuals 

 each of males and females were sampled (Fig. 3). This 

 group offish (ranging in FL from 24 to 34 cm) is fairly 

 representative of the adult silver hake population 

 sampled. The mean stomach content weight (Fig. 

 3A), percentage crustaceans (Fig. 3B), and per- 



centage fish and squid (Fig. 3C) data presented 

 graphically illustrate the differences between the 

 diet of male and female silver hake of the same 

 length. The stomachs of females contain more food, 

 on the average, than those of males; the stomachs of 

 males contain higher percentages of crustaceans 

 than females; and the stomachs of females contain 

 more fish and squid than those of males. Adjustment 

 (by stomach tissue weight) of the mean stomach con- 

 tent weights given in Figure 3A revealed that the 

 stomachs of females contain, on the average, 1.5 

 times the quantity of food found in the stomachs of 

 males. 





o 



O 

 u 



I 

 o 



< 



O 





30 



2.0 

 10 



100 



80 

 60 

 40 

 20 

 100 

 80 

 60 

 40 

 20 



1 1 I I 1 1 



MEAN TOTAL CONTENTS ( G ) 



1 T 



CRUSTACEANS 



L 



24 25 26 27 28 29 30 31 32 3 3 34 

 FISH LENGTH ( FL IN CM ) 



FIGURE 3. — A) Mean stomach content weight of male and female 

 silver hake versus fish length, B) percentage of total stomach con- 

 tent weight made up by crustaceans for male and female silver 

 hake, C) percentage of total stomach content weight made up by 

 fish and squid for male and female silver hake. 



Diurnal Variation in Feeding 

 Intensity 



The adjusted mean stomach content weight data 

 presented in Figures 4 and 5 indicate the feeding 

 periods of silver hake vary by season and size of fish. 

 In autumn, the stomachs of larger fish (24-35 cm FL) 

 are fullest just after midnight, while smaller fish (4-15 

 cm FL) have the fullest stomachs in late afternoon 



25 



