Tayior and Gervasi: Feeding habits and dietary overlap of age-0 flounder 
179 
r 
I "j Amphipod Mysid 
Copepod I j Sand shrimp 
May 
Jun 
Jul 
May Jun 
TR2 
TR4 ( ND ) 
Aug-Sep 
Ju! Aug-Sep 
A May(Rl) A Jun (Rl) L Jul (Rl) A Aug-Sep (Rl) 
|#May(R2) O Jun (R2) C Jul (R2) O Aug-Sep (R2) 
iV!ay{R4) O Jun (R3) B Jul (R3) □ Aug-Sep (R3) 
OJun(R4) < Jul(R4) O Aug-Sep (R4) 
I ♦ iV!ay(F 
B 
D 
-40 
-40 -20 0 20 40 60 
PC01 (66.5% of total variation) 
40' 
20 ' 
- 20 ' 
-40 
Mysid Copepod 
-40 -20 0 20 40 60 
PC01 (55.4% of total variation) 
Figure 7 
Contributions of prey taxa to the diet of summer flounder (Paralichthys dentatus) collected during 2009-2015 in the (A, 
B) Seekonk River and (C, D) Taunton River, as a function of month (May-September) and site (SR1-SR4; TR1-TR4). (A, 
C) Dietary contributions of prey are expressed as the index of relative importance, and (B, D) data points from principal 
coordinate analysis (PCO) are projected in space according to their actual dissimilarities. Arrows superimposed on the 
PCO biplots represent vectors of dominant prey taxa, and vectors correspond with the monotonic relationships between 
the dietary importance of a prey and the PCO axes. The first (PCOl) and second (PC02) ordination axes correspond with 
month and site, respectively, and quantify the percentage of total variation in diet of summer flounder. ND signifies no data. 
PCO biplots and again verified that copepods and, to 
a lesser extent, amphipods were shared prey among 
small and small-medium winter and summer flounder 
(Fig. 8). Prey vectors also illustrated the positive cor¬ 
relations between winter and summer flounder TL and 
the discrepancies in their respective diets. For example, 
although amphipods remained an important prey for 
both species, moderate- and large-size winter flounder 
also fed on polychaetes, bivalves, and isopods, whereas 
sand shrimp and fish became increasingly important to 
the diet of summer flounder (Fig. 8). 
The Schoener index indicated minimal dietary over¬ 
lap for winter and summer flounder when calculations 
were made independent of body size {a=0.20; Table 2). 
For winter and summer flounder of equivalent sizes, 
however, dietary overlap was inversely related to to¬ 
tal length (logarithmic regression: F=13.90, r^^O.lSG, 
P<0.0005) (Fig. 4C). Moderate to high dietary overlap 
occurred among winter and summer flounder at sizes 
<40 mm TL (a>0.4), and that overlap was due to their 
mutual reliance on copepods, as described previously 
(Figs. 5-7). There was also evidence of resource sharing 
among winter and summer flounder as large as 85 mm 
TL (Fig. 4C), and that resource sharing was attributed 
to both species continually feeding on amphipods (Figs. 
5-7). There was a spatial component to dietary overlap, 
as well, such that similarities in the diet composition 
of winter and summer flounder were most prevalent in 
