BOWMAN: FOOD OF SILVER HAKE 



each prey group made up of the total stomach con- 

 tents weight. All tables follow a standard format to 

 aid in making comparisons. In the tables, subtotals of 

 the percentage weight of major stomach content 

 groups are offset to the left. The minor prey groups 

 are discussed in further taxonomic detail in the text. 

 Adjusted stomach content weights are weights ad- 

 justed by a correction factor which allows direct com- 

 parison of the stomach content weights of different- 

 sized fish. Adjustment of the stomach content 

 weights was necessary, before any quantitative com- 

 parisons could be made between variables such as 

 sex or area. Observations on stomach tissue weight 

 (excluding contents), mean stomach content weight, 

 and whole fish weight (Fig. 2) revealed that neither 

 the mean stomach content weight nor the stomach 

 tissue weight is proportional to the body weight of 

 different-sized fish. Stomach tissue weights of 526 

 silver hake were gathered during a study jointly con- 

 ducted by American and Soviet scientists on Georges 

 Bank, September 1978, aboard the Soviet RV Belo- 

 gorsk (operated by the Atlantic Research Institute of 

 Marine Fisheries and Oceanography, Kaliningrad, 

 USSR). Mean stomach content weight data were 

 derived from the 1973-76 food data given in this 

 report, and the fish body weights were calculated us- 

 ing the silver hake length-weight equation described 

 bv Wilk et al. (1978). Silver hake weighing < 100 g, or 

 >300 g, have larger stomachs (stomach tissue weight 

 being an indication of stomach size), and stomachs 



which contain on the average more food in terms of 

 percentage body weight, than fish weighing between 

 100 and 300 g. Since both the stomach tissue weight 

 and the mean stomach content weight were dis- 

 proportionate when presented as percentage body 

 weight for different-sized fish (but were generally 

 proportionate relative to each other), and because 

 the mean stomach content weight data was much 

 more variable than the stomach tissue weight data, 

 the data adjustment was based on stomach tissue 

 weight rather than on body weight or mean stomach 

 content weight. The following equation was used to 

 adjust the stomach content weights: 



A L = 



xl 

 wl 



where 



A= Adjusted stomach content value. 

 The adjusted stomach content value 

 was converted to grams by multiply- 

 ing it by the stomach tissue weight of 

 a 30 cm FL fish. 



xl = Mean stomach content weight of all 

 fish at a given length. 



wl = Mean stomach tissue weight of silver 

 hake at a given length. 



The adjusted stomach content data for fish 4 (0.3 g) 

 to 15 (21 g) cm FL and 24 (90 g) to 35 (292 g) cm FL 

 are presented separately in forthcoming sections. 



3 



2 5 



O i STOMACH TISSUE WEIGHT/ BODY WEIGHT 



EXPONENTIAL CURVE FIT r 2 = 091, =0 107, b *0092 



x STOMACH CONTENT WEIGHT/ BODY WEIGHT 

 ,2 ., 



EXPONENTIAL CURVE FIT r^ = O 94, a = 006, b = 170 



200 300 



BODY WEIGHT (G) 



400 



500 



FIGURE 2. — Percentage body weight made up by the stomach tissue weight and the stomach content 

 weight of different size silver hake. Area enclosed by solid lines represents more than 80% (excluding 

 juveniles) of the silver hake population (fish 2-7 yr old), based on survey data. Stomach tissue weight/fish 

 length and stomach content weigh t/fish length data were fit to an exponential curve (formjy = ae bx ). The 

 data are presented in terms of body weight for illustrative purposes. 



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