562 
Fishery Bulletin 115(4) 
Table 3 
Size range and mean size, with standard error (SE), of dominant (>1% total catch) nekton species during day 
versus night in the shore zone and nearshore area of lower Delaware Bay (see Fig. 1) during June, July, and Au¬ 
gust 2013. Size was measured in fork length (FL), total length (TL), or carapace width (CW). Length comparisons 
(P-value column) are from one-factor analysis of variance (ANOVA) or Kruskal-Wallis H test, when unequal vari¬ 
ances violated assumptions of the ANOVA. The critical level of significance was adjusted from a=0.05 to a=0.01 
to account for multiple testing. 
Day 
Night 
P-value: 
day vs. night 
Species 
Size range 
(mm) 
Mean size 
(SE) 
Size range 
(mm) 
Mean size 
(SE) 
Shore zone 
Auction mitchilli 
FL: 30-115 
60.23 (17.33) 
35-94 
58.92 (8.00) 
0.090 
Brevoortia tyrannus 
FL: 68-112 
84.79 (11.54) 
55-89 
70.57 (14.06) 
0.002** 
Callinectes sapidus 
CW: 30-170 
132.22 (44.38) 
15-180 
135.5 (27.55) 
0.230 
Cynoscion regalis 
TL:38-74 
52.5 (15.33) 
47-294 
65.17 (28.14) 
0.050 
Leiostomus xanthurus 
FL:70-196 
111.8 (49.44) 
65-219 
136.4 (49.01) 
0.970 
Menidia menidia 
FL: 35-125 
76.62 (10.76) 
34-138 
74.03 (11.86) 
0.100 
Mugil cephalus 
FL: 57-187 
88.02 (33.81) 
65-158 
128.15 (25.8) 
<0.001*** 
Pomatomus saltatrix 
FL: 24-155 
100.82 (23.67) 
89-205 
123.65 (29.67) 
0.030 
Nearshore area 
Anch oa mitchilli 
FL: 30-111 
66.04 (14.08) 
26-110 
68.36 (11.38) 
0.080 
Cynoscion regalis 
TL: 43-215 
141.75 (30.62) 
45-232 
136.26 (37.37) 
0.143 
Leiostomus xanthurus 
FL: 98-188 
142.57 (18.66) 
60-193 
139.54 (24.05) 
0.117 
Micropogonias undulatus 
TL: 155-227 
195.18 (16.34) 
147-195 
181.86 (16.78) 
0.050 
Peprilus triacanthus 
FL:32-143 
103.53 (31.51) 
95-135 
115.33 (9.41) 
0.060 
Concurrent sampling of stomach contents was con¬ 
ducted to identify feeding patterns of selected domi¬ 
nant species (Torre and Targett, 2017), providing an 
opportunity to consider the potential role of predator- 
prey dynamics in the diel differences seen in shore- 
zone nekton. Stomach content data from juvenile blue- 
fish (mean: -100 mm FL) collected in the shore zone 
during daytime (Torre and Targett, 2017) showed that 
they were feeding exclusively on juvenile (<20 mm FL) 
Atlantic silverside and bay anchovy. Although these 
prey were too small to be quantitatively sampled by 
the seine net, we saw large numbers of both species 
in this size range temporarily retained in the net dur¬ 
ing daytime sampling, but not at night, despite clear 
nighttime visibility provided by headlamps. A small 
number of these fish species were in the net when it 
was brought onto the beach but were not retained as 
the net was being moved to where the contents were 
counted. It is important to note that these small At¬ 
lantic silverside and bay anchovy showed a different 
diel abundance pattern than that of larger individuals 
(mean: Atlantic silverside, -75 mm FL; bay anchovy, 
-60 mm FL) that were vulnerable to the seine net and 
which were either not significantly different in abun¬ 
dance during day and during night (Atlantic silverside) 
or were higher in abundance at night (bay anchovy). 
We speculate that the small Atlantic silverside and 
bay anchovy were abundant in the shore zone during 
the day because the shallow waters are a relative pre¬ 
dation refuge (Torre and Targett, 2017). The bluefish is 
characterized as a daytime active predator on account 
of their visual capabilities (Horodysky et ah, 2008), 
and Buckle and Conover (1997) observed that gut full¬ 
ness of young-of-the-year bluefish in the Hudson River 
estuary was highest during the day. These small At¬ 
lantic silverside and bay anchovy were preyed upon by 
the small bluefish in the shore zone because bluefish 
become piscivorous relatively early in life (Scharf et 
ah, 2009); however, predation mortality would still be 
reduced in comparison with that in adjacent deeper 
water with higher numbers of larger piscivorous fishes 
(Baker and Sheaves, 2007). Additionally, Yeoh et al. 
(2017) reported increased abundance of atherinids (sil- 
versides) and other small pelagic fishes in the shore 
zone during the day. 
In contrast, juvenile weakfish were present in greater 
density in the shore zone at night and stomach content 
analysis of these individuals (Torre and Targett, 2017) 
showed that they were feeding almost exclusively on my¬ 
sid shrimp (Neomysis americana). Weakfish are crepus¬ 
cular and nocturnal predators (Horodysky et ah, 2008) 
and this mysid species is known to undergo migration 
into surface or shallow waters during night (Hulburt, 
1957; Hopkins, 1965). Grecay and Targett (1996) found 
that although feeding by juvenile weakfish was signifi¬ 
cantly reduced under dark conditions in the laboratory, 
fish were able to feed effectively if mysids occurred at 
sufficiently high density. Therefore, it is possible that 
weakfish moved into the shore zone at night in response 
to the higher concentrations of mysid shrimp. 
