766 



Fishery Bulletin 97(4), 1999 



the prey to predator FL ratios for summer-spawned 

 bluefish were higher in 1995 than they were in 1994 

 (Fig. 3). Summer-spawned bluefish consumed rela- 

 tively larger bay anchovies in 1995 than in 1994; this 

 was due to both the smaller size of the summer- 

 spawned cohort in 1995 and the larger bay anchovy 

 prey. A linear function describing bluefish capture 

 success as a function of prey length to bluefish length 

 ratio from Scharf et al. ( 1998b) is also plotted in Fig- 

 ure 3 (capture success data for bluefish feeding on 

 Atlantic silversides). The distribution of ratios for 

 both spring- and summer-spawned bluefish in 1994 

 and spring-spawned bluefish in 1995 are values for 

 which bluefish have relatively high capture success; 



Table 5 



The total number of prey (n i found either fresh or digested 

 (fresh=no sign of digestion; digested=prey skinless to be- 

 ing only identifiable by skeleton or shape) in spring- and 

 summer-spawned young-of-the-year bluefish stomachs and 

 the percentage contribution of bay anchovy, striped an- 

 chovy, butterfish, and squid for these categories. Bluefish 

 were captured during 1994 and 1995 National Manne Fish- 

 eries Service autumn bottom trawl sur\'eys. Bluefish were 

 collected from three geographical locations of the Mid- 

 Atlantic Bight continental shelf (SNE=Southern New En- 

 gland. C-D=Chesapeake Bay to Delaware Bay, and SOC= 

 South of Chesapeake Bay, after Munch 1997). 



Spring- 

 spawned 



Summer- 

 spawned 



Location Prey type 



No. No. No. No. 



fresh digested fresh digested 



(%) (%) (%) i%) 



1994 

 SNE 



C-D 



199.5 



SNE 



C-D 



bay anchovy 



striped anchovy 



butterfish 



squid 



n 



bay anchovy 



striped anchovy 



butterfish 



squid 



bay anchovy 



striped anchovy 



butterfish 



squid 



n 



bay anchovy 



striped anchovy 



butterfish 



squid 



19 



89.5 

 5.3 

 5.3 

 



46 



89.1 

 2.2 

 2.2 

 6.5 



30 



73.3 

 6.7 

 3.3 



16.7 



21 



81.0 



19.0 

 

 



51 

 56.9 



7.8 

 33.3 



2.0 

 107 

 76.6 



2.8 



7.5 

 13.1 



19 



68.4 

 10.5 

 15.8 



5.3 

 82 

 82.8 

 13.8 







3.4 



36 



100 















31 



104 

 97.1 

 



1.0 

 2.0 



57 



36 



160 

 140 

 120 



100 H 



80 

 60 

 40 

 20 



D 



D 



»o 



D 



o<5b 2f 



^*aiKi*^ 



160 



140 



120 



100 



80 



60 



40 



20 







"1 r 



B 





50 



I I 1 1 — 



100 150 200 250 



Bluefish fork length (mm) 



300 



Figure 1 



Prey total length i mantle length for squid I versus YOY 

 bluefish fork length in (A) 1994 {prey TL=0.134 x blue- 

 fish FL+20.S2&. r2=0.10, P<0.0001) and (B) 1995 (prey 

 TL=0.041 X bluefish FZ.-h44.538, r2=0.02, P=0.027). 



Table 6 



Prey selectivity (Chesson's n, see text for calculations) in 

 YOY bluefish collected on the U.S. east coast continental 

 shelf in the autumn of 1994 and 1995. Values of a =l/m 

 (where "m" is the number of prey categories) represent ran- 

 dom feeding, whereas values of or > 1/m or a < 1/m repre- 

 sent "selection" and "avoidance" of prey, respectively. Val- 

 ues significantly different from 1/m (/-test, P<0.05) are in- 

 dicated by a (-(-) for "selection" or I-) for "avoidance". 



Prey type 



1994 



(l/m=0.25) 



1995 



(l/m=0.33) 



Bay anchovy 

 Butterfish 

 Squid 

 Other 



0.69 (-h) 

 0.12 (-) 

 0.09 (-) 



on (-1 



0.80 ( -I") 

 0.03 (-) 

 0.18 (-) 



