Torre et al.: Abundance and diversity of fish species and blue crab in Delaware Bay 
561 
Table 2 
Frequency of occurrence and mean density (individuals/100 m 2 ), with standard error (SE), of dominant (>1% total catch for 
diel period) nekton taxa during day versus night in the nearshore area of lower Delaware Bay (see Fig. 1) from June through 
September 2013. Significant differences in mean density between day and night are indicated by asterisks according to the 
criteria: *=P<0.01, **=P<0.005, ***=P<0.001. The critical level of significance was adjusted from a=0.05 to a=0.01 to account 
for multiple testing. Taxa unique to the nearshore area (not observed in the shore zone) are denoted by n . N/A=no statistical 
comparison was made because of low abundance. 
Total Day Night 
Species (or family) 
Number 
% catch 
Frequency 
of 
occurrence 
Mean 
density 
(SE) 
Frequency 
of 
occurrence 
Mean 
density 
(SE) 
P-value: 
day vs. 
night 
All taxa 
3153 
100.00 
100.0 
4.38 (1.20) 
100.0 
3.07 (0.65) 
0.71 
Anchoa mitchilli 
2300 
72.95 
100.0 
3.59 (1.26) 
100.0 
1.86 
0.11 
Leiostomus xanthurus 
346 
10.97 
77.8 
0.41 (0.25) 
100.0 
0.49 
0.28 
Cynoscion regalis 
285 
9.04 
66.7 
0.28 (0.15) 
77.8 
0.61 
0.11 
Peprilus triacanthus 
57 
1.81 
66.7 
0.11 (0.04) 
55.6 
0.12 
0.44 
Micropogonias undulatus 
40 
1.27 
66.7 
0.13 (0.03) 
33.3 
0.05 
0.03 
Callinectes sapidus 
28 
0.89 
44.4 
0.04 (0.01) 
88.9 
0.05 
N/A 
Pomatomus saltatrix 
16 
0.51 
44.4 
0.05 (0.01)’ 
55.6 
0.03 
N/A 
Selene vomer 
16 
0.51 
44.4 
0.04 (0.01) 
33.3 
0.06 
N/A 
Mustelus canis n 
13 
0.41 
33.3 
0.02 (<0.01) 
66.7 
0.03 
N/A 
Trinectes maculatus n 
9 
0.29 
22.2 
0.08 (0.03) 
11.1 
0.02 
N/A 
Pogonias cromis 
8 
0.25 
11.1 
0.02 
33.3 
0.05 
N/A 
Urophycis regia n 
8 
0.25 
22.2 
0.05 (0.01) 
44.4 
0.02 
N/A 
Bairdiella chrysoura 
6 
0.19 
11.1 
0.11 
22.2 
0.02 
N/A 
Menticirrhus saxatilis 
4 
0.13 
11.1 
0.02 
11.1 
0.06 
N/A 
Paralichthys dentatus 
3 
0.10 
0.0 
0.00 
33.3 
0.02 
N/A 
Gymnuridae „ 
2 
0.06 
0.0 
0.00 
22.2 
0.02 
N/A 
Prionotus carolinus n 
2 
0.06 
0.0 
0.00 
22.2 
0.02 
N/A 
Syngnathus fuscus 
2 
0.06 
11.1 
0.02 
11.1 
0.02 
N/A 
Brevoortia tyrannus 
1 
0.03 
11.1 
0.02 
0.0 
0.00 
N/A 
Chilomycterus schoepfii 
1 
0.03 
0.0 
0.00 
11.1 
0.02 
N/A 
Pseudopleuronectes americanus 
1 
0.03 
0.0 
0.00 
11.1 
0.02 
N/A 
Raja eglanteria „ 
1 
0.03 
0.0 
0.00 
11.1 
0.02 
N/A 
Trachinotus carolinus 
1 
0.03 
11.1 
0.02 
0.0 
0.00 
N/A 
of the variation in species assemblage in the shore 
zone (F=5.871, coefficient of multiple determination 
[F 2 ]=0.170, P<0.001), whereas site (F=0.336, F 2 =0.009, 
P=0.956) and interaction (F=0.289, F 2 =0.008, P=0.968) 
were not significant. No difference in the species as¬ 
semblage was identified in relation to day and night 
in the adjacent nearshore area (F=T.506, F 2 =0.086, 
P=0.185). 
Discussion 
We observed clear diel differences in nekton assem¬ 
blage along the sandy beach shore zone in Delaware 
Bay and greater nekton density and higher species 
richness at night. Diel patterns were also evident in 
many of the most abundant species; higher densities 
were found at night in most cases. Ordination plots 
revealed distinct day and night groups (see Fig. 4) but 
showed a large spread within groups, which can be ex¬ 
plained by seasonal variation in species assemblages, 
and which could be reduced with a shorter sampling 
period. These results expand on those noted by Torre 
and Targett (2016) and highlight the importance of in¬ 
vestigating assemblage dynamics across the diel cycle. 
Interaction between predators and prey is a major 
process driving the distribution of shallow water es¬ 
tuarine nekton (Baker and Sheaves, 2007; Becker and 
Suthers, 2014; Yeoh et al., 2017). Responding to preda¬ 
tion pressure, prey species and small juveniles of larger 
species alter their distribution to inhabit shallow water 
refuge areas where low abundance of large, primarily 
piscivorous fishes is generally thought to decrease pre¬ 
dation (Baker and Sheaves, 2007; Becker and Suthers, 
2014). Predator-prey interactions are dynamic over the 
diel cycle because many piscivorous fishes use sight to 
locate and capture prey (Horodysky et al., 2008; Yeoh 
et al., 2017). On the basis of this concept and because 
abiotic conditions were similar for day and night, we 
believe the diel differences in shore-zone nekton ob¬ 
served in our study are largely driven by day and night 
differences in predator-prey dynamics. 
