STONER: FEEDING ECOLOGY OF LAGODON RHOMBOIDES 



and the standing crops of each group were calcu- 

 lated. 



Plants were quantitatively sampled (Livingston 

 et al. 1976) at the field quadrant from where 

 macrobenthic animals were collected, on the fish 

 collection date. Data on the biomass and species 

 composition of benthic macrophytes at the field 

 stations were provided by Robert J. Livingston. 



Fish, macrophytes, and prey animals were col- 

 lected monthly from November 1976 to December 

 1977. All collections for a station were made on the 

 same date at midday, and all of the stations were 

 sampled within a 2-4 day period. 



For analysis of stomach contents, fish were 

 placed in 5 mm size classes up to 40 mm SL, 10 mm 

 size classes from 40 to 100 mm, and 20 mm size 

 classes for fish >100 mm SL. Food items taken 

 from the stomachs of up to 25 fish in a size class 

 were pooled for each sampling date and station 

 and preserved with lQ9c isopropanol and a dilute 

 solution of rose bengal stain. The gravimetric 

 sieve fractionation procedure developed by Carr 

 and Adams (1972) was used to analyze stomach 

 contents of pinfish ranging from 11 to 160 mm SL. 

 Stomach contents were washed through a series of 

 six sieves of decreasing mesh size (2.0-0.075 mm 

 mesh) and the frequency of occurrence of each food 

 type was recorded for each sieve fraction. Because 

 all of the items in a particular sieve fraction were 

 of comparable size, the relative proportion of the 

 stomach contents made up of each food type was 

 measured directly by counting. After examina- 

 tion, each sieve fraction was dried overnight at 

 100° C and the total contribution of each food type 

 was calculated. 



With two exceptions, each food particle was 

 placed in a mutually exclusive category. General 

 categories such as amphipod, isopod, harpacticoid 

 copepod, crab zoea, and mysid were employed. The 

 categories animal remains (unidentified tissue 

 stained with rose bengal) and plant remains were 

 the only food categories that were not mutually 

 exclusive from other groups. Plants specifically 

 identified were T. testudinum and S. fili forme. The 

 general food categories, 40 in number (Table 1), 

 were used for statistical analyses; however, 

 whenever an animal or plant could be identified to 

 a more specific group (e.g., family, genus, species) 

 this information was recorded. 



Cluster analysis, employing the similarity 

 coefficient, p (Matusita 1955; Van Belle and 

 Ahmad 1974), and flexible grouping cluster 

 strategy ((3 = -0.25) was used to describe onto- 



Table 1. — List of the general food categories encountered in 

 the stomachs of pinfish and the codes employed in food habit 

 histograms. 



genetic variation in food habits of L. rhomboides. 

 The appropriateness of the cluster strategy for 

 dealing with fish diet data was discussed by Sheri- 

 dan (1978). 



Stepwise multiple regression was used in cer- 

 tain instances to analyze the relationships be- 

 tween amounts of food items consumed by pinfish 

 and abundance of food items in the field. Depen- 

 dent variables included the amount of amphipod, 

 shrimp, and plant material in stomachs (percent of 

 contents in dry weight) and independent variables 

 were amphipod, shrimp, plant, calanoid copepod, 

 and polychaete abundance values. Maximization 

 of the coefficient of determination, r^, was the 

 criterion for selecting the best multiple regression 

 model. The minimum F value for inclusion of vari- 

 ables in the regression equations was set at 0.01. 



RESULTS 



Nearly 5,000 pinfish, representing 61% of all 

 trawlable ichthyofauna in Apalachee Bay, were 

 collected at four field sites during a 1-yr sampling 

 period. The number offish collected at a station, 

 however, was a direct function of the mean macro- 

 phyte biomass at the site (r = 0.998, P>0.01). 

 Most of the fish were collected between April and 

 October (Figure 2). 



The stomach contents of 2,174 pinfish taken 

 from the four field sites were analyzed. Although 

 the unvegetated site (Fenholloway 11) produced 

 only 82 pinfish in routine trawl collections, over 

 600 stomachs of fish from each of the vegetated 



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