556 
National Marine 
Fisheries Service 
NOAA 
Abstract —Diel sampling was con¬ 
ducted during June-September 
2013, in the shore zone and adjacent 
nearshore zone of Delaware Bay, 
Delaware, to identify day and night 
changes in nekton density, species 
richness, and the species assem¬ 
blage. Mean species richness and to¬ 
tal nekton density in the shore zone 
were higher at night. A detailed 
examination of abundant species 
revealed that bay anchovy ( Anchoa 
mitchilli ), weakfish (Cynoscion re- 
galis), spot ( Leiostomus xanthurus), 
and blue crab ( Callinectes sapidus) 
occurred in higher densities in the 
shore zone at night than during the 
day. Bluefish ( Pomatomus saltatrix ) 
occurred in higher densities during 
the day. Additionally, small (<20 mm 
in fork length) Atlantic silverside 
(Menidia menidia) and bay anchovy, 
were observed in abundance in the 
shore zone only during daytime. Day 
and night differences in predator- 
prey dynamics were likely a primary 
driver of diel differences in nekton 
abundances observed in the shore 
zone. No diel differences in species 
richness, nekton density, or spe¬ 
cies assemblage were found in the 
adjacent nearshore area. Daytime 
sampling predominates in studies of 
shore-zone nekton and our results 
show the value of also sampling at 
night. Future research should in¬ 
clude samples throughout the diel 
cycle and include tagging and move¬ 
ment data to allow a better under¬ 
standing of diel dynamics of nekton 
along sandy beach shores. 
Manuscript submitted 16 December 2016 
Manuscript accepted 29 August 2017. 
Fish. Bull. 115:556-565 (2017). 
Online publication date: 19 September 2017. 
doi: 10:7755/FB.115.4.11 
The views and opinions expressed or 
implied in this article are those of the 
author (or authors) and do not necessarily 
reflect the position of the National 
Marine Fisheries Service, NOAA. 
Fishery Bulletin 
established in 1881 -<?. 
Spencer F. Baird 
First U S Commissioner 
of Fisheries and founder 
of Fishery Bulletin 
Diel differences in abundance and diversity of fish 
species and blue crab (Callinectes sapidus) in the 
sandy beach shore zone of lower Delaware Bay 
Michael P. Torre (contact author) 
Danielle M. Lifavi 
Timothy E. Targett 
Email address for contact author: torrem27@gmail.com 
School of Marine Science and Policy 
University of Delaware 
112 Smith Laboratory 
Lewes, Delaware 19958 
Present address for contact author: School of Marine Sciences 
University of Maine 
223 Libby Hall 
Orono, Maine 04469 
Estuarine and ocean shore zones are 
known to support high nekton densi¬ 
ties worldwide (Whitfield, 1999; Fe¬ 
lix et ah, 2007; Gondolo et al., 2011). 
Sandy beaches dominate the world’s 
shorelines and are productive habi¬ 
tats serving important functions as 
nursery areas and migration path¬ 
ways (McLachlan and Brown, 2006; 
Marin Jarrin and Shanks, 2011; Ro¬ 
drigues and Vieira, 2013). Estuar¬ 
ies along the east coast of the U.S. 
are no exception and support many 
ecologically and economically impor¬ 
tant species during one or more of 
their life stages and are essential for 
the maintenance of coastal fisheries 
(Beck et al., 2001; Able et al., 2010). 
Nekton assemblages along sandy 
estuarine beaches and ocean surf 
zones vary spatially and temporally 
in response to the dynamic nature of 
these environments (Layman, 2000; 
Marin Jarrin and Shanks, 2011). 
These dynamics include day-night 
changes which are reflected in the 
abundance and diel movement of 
many of the dominant shore zone 
species (Gibson and Robb, 1996; 
Becker and Suthers, 2014; Bennett 
et al., 2015). Interaction between 
predator and prey species is a ma¬ 
jor process driving the distribution 
of estuarine nekton as prey alter 
their distribution to inhabit shal¬ 
low water refuge areas (Becker and 
Suthers, 2014). Despite the impor¬ 
tance of diel variation, most stud¬ 
ies of sandy beach shore zones have 
been conducted during the daytime, 
a period that allows the capture of 
only a portion of assemblage dynam¬ 
ics (Rountree and Able, 1993; Becker 
and Suthers, 2014). 
Previous studies of diel variation 
in shore zone nekton assemblages 
have generally reported increased 
species richness, catch per unit of ef¬ 
fort (CPUE) or density during night¬ 
time (or both) (Horn, 1980; Ross et 
al., 1987; Layman, 2000; Gaelzer and 
Zalmon, 2008; Vasconcellos et al., 
2010, 2011; Yeoh et al., 2017). There 
have, however, also been reports of 
greater species richness or higher 
densities of shore zone fish species 
(or both) during the day (Godefroid 
et al., 1998; Pessanha and Araujo, 
