Taylor and Gervasi: Feeding habits and dietary overlap of age-0 flounder 
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Table 1 
Summary of environmental and biological characteristics at individual sites in the Seekonk River (SR) and Taunton River 
(TR) in Rhode Island and Massachusetts, respectively, where winter flounder (Pseudopleuronectes americanus) and summer 
flounder (Paralichthys dentatus) were collected during 2009-2015. Values represent annual means, with standard errors 
(SEs), and ranges of measurements taken per sampling effort across months (May-September). Environmental data include 
water temperature (°C), salinity, and dissolved oxygen (mg/L), and biological data include abundance (individuals/100 m^) 
and “fresh” (i.e., measured immediately after capture) total length (mm) of winter flounder (WF) and summer 
flounder (SF). 
Seekonk River 
Taunton River 
Site 
SRI 
SR2 
SR3 
SR4 
TRl 
TR2 
TR3 
TR4 
Environmental characteristics 
Temperature 
Mean 
22.9 (SE 1.1) 
23.5 (SE 1.2) 
23.6 (SE 1.3) 
23.2 (SE 1.1) 
23.0 (SE 1.3) 
23.5 (SE 1.4) 
22.8 (SE 1.5) 
22.9 (SE 1.4) 
Range 
Salinity 
19.0-26.8 
19.5-27.8 
17.6-28.4 
19.4-26.8 
17.8-26.8 
18.1-26.9 
17.9-24.9 
17.7-26.5 
Mean 
5.0 (SE 1.3) 
7.2 (SE 1.7) 
8.3 (SE 1.5) 
10.7 (SE 2.0) 
3.2 (SE 1.1) 
8.9 (SE 1.7) 
7.4 (SE 1.3) 
19.5 (SE 1.6) 
Range 
Dissolved oxygen 
1.7-10.6 
2.8-13.8 
3.3-14.1 
4.3-18.0 
0.3-7.4 
3.6-15.6 
4.2-10.2 
12.3-24.0 
Mean 
7.2 (SE 0.8) 
7.5 (SE 0.7) 
8.8 (SE 1.0) 
8.5 (SE 0.8) 
6.5 (SE 0.5) 
7.1 (SE 0.6) 
7.7 (SE 0.6) 
6.8 (SE 0.6) 
Range 
4.4-9.9 
4.7-9.7 
5.0-12.3 
5.9-10.9 
4.7-8.1 
5.2-9.7 
6.3-9.1 
4.8-9.1 
Biological characteristics 
WF abundance 
Mean 
92.4 (SE 44.4)42.8 (SE 22.2) 
6.8 (SE 4.2) 
16.2 (SE 5.8) 
1.6 (SE 0.7) 
5.1 (SE 2.3) 
2.4 (SE 0.3) 
7.3 (SE 3.0) 
Range 
WF total length 
5.6-286.1 
2.4-136.2 
0.0-26.8 
4.8-42.4 
0.06-4.3 
1.2-16.5 
2.0-3.4 
1.5-21.8 
Mean 
52.6 (SE 4.7) 
49.7 (SE 3.9) 
49.2 (SE 3.3) 
54.5 (SE 3.0) 
64.5 (SE 3.4) 
52.7 (SE 4.5) 
55.2 (SE 5.0) 
53.9 (SE 2.5) 
Range 
SF abundance 
26.9-85.0 
26.4-76.3 
34.8-70.2 
32.8-75.0 
23.0-87.0 
28.4-77.2 
27.5-85.2 
37.8-70.8 
Mean 
10.5 (SE 4.7) 
5.7 (SE 3.6) 
5.5 (SE 3.8) 
3.2 (SE 2.2) 
1.0 (SE 0.6) 
2.1 (SE 1.2) 
1.7 (SE 0.7) 
0.05 (SE 0.04) 
Range 
SF total length 
1.7-33.2 
0.08-24.5 
0.0-23.6 
0.06-14.3 
0.2-3.8 
0.1-7.8 
0.3-2.8 
0.0-0.3 
Mean 
80.4 (SE 12.0) 84.3 (SE 13.3) 
65.7 (SE 3.6) 77.7 (SE 11.2) 88.9 (SE 14.9) 91.1 (SE 12.1) 97.8 (SE 6.9) 105.2 (SE 12.0) 
Range 
31.1-155.0 
32.2-160.0 
47.7-71.0 
32.0-133.0 
37.0-137.0 
40.3-236.0 
75.4-126.0 
69.0-118.9 
year, 3-4 sites per river were sampled fortnightly with 
a beach-seine set that was 15x1.8 m in width (and had 
0.64-cm mesh size and 0.48-cm mesh size in the bunt). 
Sampling occurred during daylight (-0800-1600; ± 2 
h of low tide), and 1 haul was conducted per site per 
date. Winter and summer flounder captured during 
field sampling were counted immediately (number per 
100 square meters; Taylor et al., 2016) and measured 
to the nearest millimeter for “fresh” total length (TL) 
(Table 1, Fig. 2). For each sampling effort, <10 indi¬ 
viduals of each flounder species in a random subsample 
were preserved in 70% ethanol for subsequent stomach 
content analysis, and remaining individuals were re¬ 
turned to their place of capture. Surface temperature 
(degrees Celsius), salinity, and dissolved oxygen (mil¬ 
ligrams per liter) were also measured at each site per 
date with a handheld YSI Model 85“^ meter (YSI Inc., 
Yellow Springs, OH). The environmental conditions and 
^ Mention of trade names or commercial companies is for iden¬ 
tification purposes only and does not imply endorsement by 
the National Marine Fisheries Service, NOAA. 
biological data for winter and summer flounder across 
the sampling sites are summarized in Table 1. 
Stomach content analysis 
In the laboratory, winter and summer flounder pre¬ 
viously preserved in 70% ethanol were measured for 
“preserved” TL (in millimeters). Prey were then ex¬ 
tracted from fish stomachs and identified to the lowest 
practical taxon by using stereoscopic microscopes. The 
contribution of each prey taxon to the diet of winter 
and summer flounder was expressed by 3 component 
indices (Hyslop, 1980): frequency of occurrence (%F), 
volumetric percentage i%V}, and numeric percent¬ 
age (%A0, where %F equaled the number of stomachs 
containing a specific prey taxon divided by the total 
number of stomachs with food contents (a nonadditive 
index), %V was the visual determination of the volu¬ 
metric contribution of a prey taxon to the total stomach 
volume of a winter or summer flounder, and %N was 
the number of individuals within a prey taxon divided 
by the total number of prey identified in a stomach of 
a winter or summer flounder. 
