477 
Abstract .—We measured the daily 
abundance of larvae of eight species of 
ocean-spawned, estuarine-dependent 
fishes to determine the effect of sam- 
pling frequency on the mean and vari- 
ance estimates during larval immigra- 
tion past a permanent sampling station 
inside Beaufort Inlet, North Carolina, 
mid-November 1991 to mid-April 1992. 
Species of interest were Brevoortia 
tyrannus, Lagodon rhomboides, Leio- 
stomus xanthurus, Micropogonias undu- 
latus, Mugil cephalus, Paralichthys 
albigutta, P. dentatus, and P. lethostigma. 
Our data suggest that sampling at in- 
tervals >7 days can lead to excessive 
variance in abundance estimates. For 
all species, abundance varied as much 
as an order of magnitude from night to 
night. Proportional residuals from poly- 
nomial models of the seasonal recruit- 
ment pattern for a given species were 
used to assess the potential influence 
of nine environmental variables on 
daily densities. Twenty-seven of 72 cor- 
relations of proportional residuals with 
environmental variables were signifi- 
cant (P<0.05). Proportional residuals 
were positively correlated with time 
after dusk for six of eight species and 
were negatively correlated with turbid- 
ity for five of eight species. However, 
interpretation of correlations must be 
done cautiously because a species’ re- 
cruitment pattern may coincide with 
normal seasonal change in one or more 
environmental variables. Variability in 
transport of larvae, from offshore to 
near the inlet and then through the 
inlet to the station, probably influences 
species abundance at the sampling sta- 
tion more than locally acting environ- 
mental variables. Daily collections of B. 
tyrannus larvae provided otoliths 
(n=l,341) showing that a large number 
of younger larvae, averaging 55 days 
posthatch, arrived at the station in mid- 
March on the date of maximum observed 
daily density ( 160 larvae per 100 m 3 ). 
Manuscript accepted 6 March 1997. 
Fishery Bulletin 95:477-493 (1997). 
Daily variability in abundance of larval 
fishes inside Beaufort Inlet 
Willi am F. Hettler Jr. * 
David S. Peters 
David R. CoSby 
Elisabeth H. Laban 
Southeast Fisheries Science Center 
National Marine Fisheries Service, NOAA 
1 0 1 Pivers Island Road 
Beaufort, North Carolina 28516-9722 
*E-mail address: whettler@hatteras.bea.nmfs.gov 
From 1985 to the present, weekly 
sampling has been conducted near 
Beaufort Inlet to collect fish larvae 
entering the estuary during fall, 
winter, and spring (Warlen, 1994). 
Such inlets provide locations for 
sampling larvae in order to assess 
potential year-class strength of 
ocean-spawned but estuarine-de- 
pendent species. Abundance, size, 
and age data on early larvae in the 
sea, on advanced larvae in the in- 
lets, and on juveniles in the estuar- 
ies can be used to understand when 
significant events such as mortal- 
ity or rapid growth occur during a 
species’ early life history. To obtain 
accurate abundance, size, and age 
estimates from the population of 
recruiting larvae, appropriate sam- 
pling protocol must be employed 
(Morse, 1989; Davis et al., 1990). 
Errors resulting from sampling bias 
can arise when larvae selectively 
avoid the sampling device or when 
there is nonrandom spatial (patchy) 
distribution of the larvae (Wiebe 
and Holland, 1968). Decreasing the 
time interval between sampling and 
decreasing the distance between 
stations in ichthyoplankton surveys 
increases the resolution of tempo- 
ral or spatial patterns of species 
with patchy pelagic egg and larval 
distributions at both microscale 
(Houde and Lovdal, 1985) and mesos- 
cale levels (Rowe and Epifanio, 1994). 
Studies within NOAA’s Southeast 
Atlantic Bight Recruitment Experi- 
ment (SABRE) are attempting to 
measure fluxes of larval fishes 
across the continental shelf and 
through inlets into estuaries amid 
myriad cyclical phenomena that 
bear directly on the larvae’s abun- 
dance (Govoni and Pietrafesa, 1994; 
Stegmann and Yoder, 1996). The 
purpose of our SABRE study was to 
estimate the daily variation in 
abundance data collected on eight 
species of larval fish that seasonally 
ingress past the permanent sam- 
pling station at Pivers Island inside 
of Beaufort Inlet in order to deter- 
mine an optimum sampling fre- 
quency for future sampling proto- 
cols. For one of these species, 
Brevoortia tyrannus (Atlantic men- 
haden), which has been the focus 
species in SABRE studies, addi- 
tional analysis was conducted on 
age and growth with specimens col- 
lected daily. For all species, we used 
daily abundance data to calculate 
the decrease in precision of our rela- 
tive abundance estimates as the 
interval between sampling events 
increased. Daily collections of lar- 
vae also allowed us to measure 
changes in size (length) of all eight 
