456 



Fishery Bulletin 103(2) 



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J^ 



Size class (cm) 



Figure 2 



Ontogenetic variations of the diet diversity index (B<7±CI 9Vi ) 

 of Cynoscion nannus (n is the number of stomachs contain- 

 ing food). 



through 5 (51.1%-65.1%). The trophic spectrum of 

 the smallest C. nannus (7 cm sTL slO.9 cm, n = 67) 

 was composed by crustaceans (W^ = 68%), mostly 

 carideans and stomatopods (W^ = 2Q9c). The diet 

 of intermediate individuals (11 cm sTL sl6.9 cm; 

 /; =148 ) was composed by penaeid shrimp, fish, and 

 stomatopods. Only fish of the size classes grouped 

 in this range showed percentages of diet similarity 

 >50%. Among C. nannus between 17 and 18.9 cm 

 TL (« = 37), the value of consumed fish biomass at- 

 tained 69%, whereas that of penaeid shrimp reached 

 20%. Only among the larger individuals (19 cm sTL 

 s20.9 cm; n = 35) did cephalopods attain high gravi- 

 metric values (W^=457() followed by penaeid shrimp 

 (W £ =38%). 



Values of trophic niche breadth for each size class 

 indicated ontogenetic variation in the diet (Fig. 2). 

 The smallest individuals fed on a smaller number 

 of prey species and showed a trend towards higher 

 trophic specialization. Larger individuals, however, 

 had a wider trophic spectrum and fed on a greater 

 number of different prey species. 



Temporal variations in the dietary composition 

 of C. nannus were significant (F=3.58; P<0.05). 

 During the first months of the year, C. nannus 

 consumed a higher percentage offish ( W J = 37.2'7f ), 



