178 
Fishery Bulletin 115(2) 
Amphipod 
Copepod 
Polychaete 
I I Isopod 
Bivalve 
Other 
Aug-Sep 
A May(Rl) 
A Jun (Rl) 
A Ju!(Rl) 
A Aug-Sep (Rl) 
• Mav(R2) 
O Jun (R2) 
• Jul(R2) 
O Aug-Sep (R2) 
■ May(R3) 
□ Jun(R3) 
■ Jul(R3) 
□ Aug-Sep (R3) 
A May(R4) 
O Jun (R4) 
A Jul(R4) 
O Aug-Sep (R4) 
Figure 6 
Contributions of prey taxa to the diet of winter flounder (Pseudopleuronectes americanus) collected during 2009-2015 in the 
(A, B) Seekonk River and (C, D) Taunton River, as a function of month (May—September) and site (SRI—SR4; TR1-TR4). 
(A, C) Dietary contributions of prey are expressed as an index of relative importance, and (B, D) data points from princi¬ 
pal 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) axes correspond with month and site, 
respectively, and quantify the percentage of total variation in diet of winter flounder. ND signifies no data. 
Interspecific dietary overlap 
The diet of winter flounder and summer flounder var¬ 
ied as a function of species type and length classifi¬ 
cation (2-way PERMANOVA: species, pseudo-F=77.80, 
P<0.001; size, pseudo-P’=5.66, P<0.001). The species- 
size interaction effect also was significant, thereby pre¬ 
cluding contrasts across the main effects (2-way PER¬ 
MANOVA: speciesxsize, pseudo-F=3.02, P<0.001). With 
respect to interspecific comparisons, SIMPER analyses 
revealed that dietary similarities were highest among 
small-size winter and summer flounder (average simi¬ 
larity; 29.4%), and increasing lengths resulted in great¬ 
er deviations in their respective diets (average simi¬ 
larity among moderate and large winter and summer 
flounder: 20.3-22.3%). The higher degree of resource 
overlap among small winter and summer flounder was 
attributed to their initial feeding on copepods, followed 
by ontogenetic dietary shifts away from this shared 
prey item (Figs. 5-7). 
Similarities and differences in the diets of winter 
and summer flounder were re-affirmed by PCO (Fig. 8). 
Species type most closely corresponded with the PCOl 
and accounted for 40.6% of the explainable variation 
in diet. Conversely, body size of winter and summer 
flounder explained 14.4% of the total variation in diet 
and was visually represented by the PC02. Vectors of 
the dominant prey taxa were superimposed onto the 
