FISHERY BULLETIN: VOL 76, NO. 1 



and then decreased for larger fish. Other prey 

 categories either did not show regular trends or 

 remained relatively constant in occurrence be- 

 tween size classes. The percent number of prey 

 showed similar trends with increasing fish size. 

 Crustacean larvae, copepods, gammarid am- 

 phipods, and cumaceans were of greater impor- 

 tance to small fish, while larger fish ( 100-140 mm) 

 utilized more lancelets and pelecypods. 



The volumetric importance o{ Branchiostoma to 

 the 41- to 60-mm size group resulted from one fish 

 capturing a single large lancelet. Volumetrically, 

 the diet of P. scitulus 80 mm and larger was domi- 

 nated by lancelets and polychaetes, while cuma- 

 ceans, copepods, and natantians (especially larval 

 forms) were of greater importance to small fish 

 (Figure 2). Brachyurans showed a more uniform 

 pattern of distribution among size groups. 



Misc 



Teleoslei 



Bronchiosfoma 



Brochyuro 



Notcntia 



Cumacea 



Copepoda 



Gammoridea 



Misc 



Teleostei 



Branchiostoma 



Brochyuro 



Notontia 



Cumacea 



Copepodo" 



Gammoridea 



Teleostei 



Bronchiostomo 



Brochyuro 



Natontia 



Cumoceo 

 Copepoda 



Gammoridea 



Misc 



Branchiostomo 



Brochyuro 



Notontio 



Cumoceo 



Gommandeo" 



Misc 



Polychoeta 



Teieostei 



BronchiosToma 



Brochyuro 



Notontia 



Cumoceo 



Gommorideo 



Misc 



Polychoeta 



Branchiostomo 



Brochyuro 



Notontia 



Gommorideo 



Misc 



Bivolvio 



Polychoeta 



Bronchiostofna 



Brochyuro 



Notontia 



GommoriBeo^ 



Misc 



Bivolvio 



Polychoeta 



Bronchiostomo 



Brochyuro 



Natontio 



Fish Length (mm) 



Figure 2. — Changes in the percent volume of major prey categories for size classes ofPrionotus scitulus, Tampa Bay, Fla., 1972-73. 



Percent Similarity 

 10 20 30 40 50 60 70 80 90 100 



r 



Trophic relationships among size groups were 

 summarized by cluster analysis based on the per- 

 cent occurrence of prey (Figure 3). Fish smaller 

 than 81-90 mm and larger than 91-100 mm formed 

 two major divisions, linking at 779^ similarity. 

 The lower similarity between size classes of small- 

 er searobins compared with larger size classes is 

 indicative of the more rapid changes in trophic 

 ontogeny occurring between small individuals. 



Figure 3. — Cluster analysis (UPGMA; unweighted pair group, 

 arithmetic average) of prey similarity between size classes of 

 Prionotus scitulus, Tampa Bay, Fla., 1972-73. Similarity was 

 determined from percent occurrence of prey categories. 



228 



