STONER: FEEDING ECOLOGY OF LAGODON RHOMBOIDES 



quency changes related to season within the 36-80 

 mm and adult size groups were minor. Because of 

 insufficient data for the site, FenhoUoway 11 was 

 ehminated from analysis of seasonal variation in 

 pinfish diet. 



Data were sufficient for seasonal analysis of diet 

 in postlarval pinfish only at Econfina 12. Pinfish 

 <16 mm SL were collected at this site from 

 January through April. In January and February, 

 postlarval pinfish consumed primarily calanoid 

 copepods, plus a small number of invertebrate 

 eggs. Later, they consumed harpacticoid copepods 

 and amphipods in large quantities, and no cal- 

 anoid copepods were taken by postlarvae in April. 

 The relative abundance of calanoid copepods and 

 invertebrate eggs in the diet of these fish coin- 

 cided directly with the absolute abundance of the 

 plankton ic food items as determined by plankton 

 tows taken on the day offish collections. Copepods 

 and invertebrate eggs were most abundant in 

 January and February, and declined to annual 

 lows in April (Table 3). Amphipod abundance re- 

 mained relatively high at Econfina 12 through the 

 winter and spring with annual minima occurring 

 in the fall. Because amphipods were most abun- 

 dant in January and February (Table 3), when 

 copepod consumption was highest, it would appear 

 that calanoid copepods are the preferred prey of 

 postlarval pinfish. Only when calanoid popula- 

 tions fell to near zero did amphipods become a 

 major portion of the diet. 



Pinfish of the carnivorous feeding group (16-35 

 mm SL) were collected from March through Au- 

 gust. In the spring and summer, amphipods and 

 harpacticoid copepods were the primary dietary 

 components of these fish (Figure 6). Clearly, how- 

 ever, amphipods were most important at Econfina 

 10. Amphipod consumption decreased with time 

 and by late summer the primary dietary compo- 

 nents were harpacticoid copepods and small 

 shrimp. A small amount of plant material was 

 taken at all three vegetated stations in midwinter. 

 Invertebrate eggs and other animal foods consis- 

 tently contributed small amounts to the diets of 

 pinfish between 16 and 35 mm SL. 



Temporal variations in diet of pinfish from 16 to 

 35 mm were analyzed by stepwise multiple regres- 

 sion using calanoid copepod, shrimp, amphipod, 

 and benthic macrophyte abundance (Table 3) as 

 independent variables. Amphipod consumption 

 was positively correlated with amphipod abun- 

 dance (except Econfina 10) and negatively related 

 to plant, shrimp, and calanoid copepod abundance. 



■D 



in 

 ■*j 

 c 

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 +j 

 c 

 o 

 U 



sz 

 (J 

 CD 



E 

 o 



1/1 



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3 4 5 6 7 8 



(20) (21) (27) (30) (31) (32) 



Month 



FIGURE 6. — Seasonality in diet of Lagodon rhomboides between 

 16 and 35 mm SL from three stations (F 12-top, E 10-middle, E 

 12-bottom) in Apalachee Bay, Fla. (March to August 1977). Diet 

 is given as the relative proportion of the dry weight of stomach 

 contents. Codes for the dietary components are given in Table 1. 

 Numbers in parentheses are the mean lengths of fish. 



At least 97.6% of the variation in amphipod con- 

 sumption was explained by three independent 

 variables for all three stations. Significant multi- 

 ple correlation values for temporal variation in 

 shrimp consumption were obtained for fish from 

 Econfina 10 and 12 (r^ = 0.986 and 0.999, respec- 

 tively) (Table 4). Shrimp consumption was posi- 

 tively correlated with shrimp abundance, plant 

 biomass, and calanoid copepod abundance. Nega- 

 tive relationships were found with amphipod 

 abundance. Harpacticoid intake was positively re- 

 lated to plant biomass. 



Pinfish between 36 and 80 mm SL were avail- 

 able year-round at vegetated sites and were consid- 

 ered to be omnivores. Examination of temporal 



343 



