FISHERY BULLETIN: VOL. 79, NO. 4 



prey in more than one predator was 20% (19/96) by 

 Tyler's (1972) method and 57% (65.5/116) by the 

 ranked principal prey method. 



Prey Size and 

 Predator Mouth Morphology 



Resource partitioning by prey size was 

 examined for several predators by means of 

 length-frequency distributions of crustacean prey. 

 Crustaceans were analyzed because of their im- 

 portance as a food group and because their hard 

 external skeletons permitted reliable mea- 

 surements. 



A comparison of three flounder species showed 

 that the winter flounder consumed the smallest 

 prey (Figure 2). The majority of the winter floun- 

 der prey ranged between 4 and 10 mm long 

 (X±95% CL = 6.8 ±0.6). The yellowtail flounder 

 prey lengths were bimodally distributed. In one 

 group most prey ranged between 5 and 10 mm, 

 while in the second they were between 14 and 17 

 mm (Z±95% CL = 10.8 ±1.3). The windowpane 

 utilized the largest prey, with most ranging be- 



H 

 Z 

 LU 

 O 



a: 



UJ 

 CL 



5 10 15 20 25 



PREY LENGTH (mm) 



30 



tweenl3andl7mm(X±95%CL = 14.4 ±0.7). 



The longhorn sculpin and Atlantic cod, were two 

 other important crustacean predators examined. 

 Longhorn sculpin prey showed a wide range in size 

 (1-30 mm) (Figure 3). The largest proportion of 

 longhorn sculpin prey was between 5 and 15 mm 

 long (X ± 95% CL = 11.1 ±0.7). The distribution of 

 cod prey sizes was similar to that of the longhorn 

 sculpin. Most of the cod prey were between 4 and 13 

 mm long (X ±95% CL = 9.0±0.7). 



Data on mouth measurements are presented in 

 Table 11. The basic mouth shape is given as the 

 ratio of the mean mouth width to mean upper jaw 



16 



8 







12 



D 



UJ 



o 



UJ 

 Q- 







16 



8 







WINTER FLOUNDER (N=23) 



X TL = 22.3 ± 3.4 



N (PREY) = 115 



xPREY LENGTH = 6.8 ±3.0 



Qnll 



n n 



YELLOWTAIL FLOUNDER (N=ll) 

 X TL = 25.3± 5.3 

 N (PREY) = 55 

 X PREY LENGTH = 10.8 ±4.9 



mm 



WINDOWPANE (N = 8) 



xTL = 27.4 ± 3.9 



N (PREY) = 50 



X PREY LENGTH = I4.4± 2.6 



I I I I 



n, ,n 



n 



2 4 6 8 10 12 14 16 18 20 

 PREY LENGTH (mm) 



Figure 2. — Prey size distributions for winter fiounder, yellow- 

 tail flounder, and windowpane. 



Figure 3. — Prey size distributions for longhorn sculpin and 

 Atlantic cod. 



782 



