Kupchik and Shaw: Age, growth, and recruitment of larval and early juvenile Micropogomas undulatus 
21 
slow-velocity rotor was positioned just off center of the 
ring to determine volume of filtered water. 
Ichthyoplankton samples were collected every 4 h 
over a 72-h period, twice monthly from early October 
through April over a 2-year period (2006-2008), except 
December and January, when samples were taken only 
on a monthly basis. In addition, there were 2 sampling 
efforts made in September 2007. The sampling season 
was chosen to coincide with wind-dominant meteoro- 
logical events (i.e., atmospheric cold front passages) 
from late fall to early spring and to increase the prob- 
ability of collecting larvae and small juveniles (Her- 
nandez et ah, 2010). Individual sampling dates were 
chosen to match the largest astronomical tidal ranges. 
During passive sampling, one icthyoplankton collec- 
tion was taken at the surface and another near the 
bottom. They were taken in random order for each 
sampling effort. Surface collections were 6 min long, 
and near-bottom collections were 10 min long to com- 
pensate for vertical differences in current speed and, 
ultimately, for volume of filtered water (i.e., sampling 
effort). For near-bottom collections, the net mouth was 
closed during deployment until the net was in position, 
was opened for sampling, and was closed for retrieval 
to prevent vertical contamination of the sample during 
transit through the water column. Surface collections 
had a mean filtered volume of 13.3 m 3 (standard de- 
viation [SD] 16.8), and near bottom collections had a 
mean filtered volume of 16.6 nr 3 (SD 22.4). Nets were 
washed down with a freshwater source to avoid biologi- 
cal contamination from marine taxa. 
Ichthyoplankton samples were fixed initially for 
approximately 3.5 h in freshly made, buffered (sodi- 
um phosphate, dibasic Na^PCV^O, and monobasic 
Na 2 HPC> 4 ) 10% formalin. Samples were then rinsed, 
thoroughly drained, and switched into a 70% ethanol 
solution. This procedure parallels methods described 
by Butler (1992). Although some studies have shown 
that formalin may damage otoliths of small specimens 
(Brothers, 1984), sagittal otoliths in other species have 
not shown evidence of dissolving (Re, 1983; Landaeta 
et ah, 2014), especially during very short exposures. 
During each collection of icthyoplankton samples, 
estuarine hydrographic parameters were measured 
dockside with a portable YSI 85 instrument (YSI Inc., 
Yellow Springs, CO). A continuously sampling YSI 600R 
multiparameter water-quality sonde (YSI Inc.), moored 
on the bottom of the channel floor offshore of the dock, 
also measured the same parameters. Hydrographic 
data were downloaded periodically as necessary and 
archived. Predicted diurnal tides were obtained from 
NOAA’s Center for Operational Oceanographic Prod- 
ucts and Services (website) for a nearby tide gauge sta- 
tion at Port Fourchon (station ID: 8762075; 29°6.8 N, 
90°11.9W). Tide height data and the difference be- 
tween the predicted and measured tidal prism were 
downloaded for that station. 
A bottom-mounted, upward-looking acoustic Dop- 
pler current profiler (ADCP), a 1200-kHz broadband 
Workhorse H-ADCP (Teledyne RD Instruments, Pow- 
ay, CA), was placed in the center of Bayou Tartellan 
(offshore of the dock), for the duration of the study, to 
measure the vertical profile of current velocity and di- 
rection. Boat surveys were also conducted along Bay- 
ou Tartellan and Bayou LaFourche out to Belle Pass 
through the use of downward-looking ADCPs to provide 
a channel-wide correction factor for the mid-channel, 
stationary upward-facing ADCP. A volume transport 
was calculated in cubic meters per second for Bayou 
Tartellan from these data. To remove the effects of tide 
and inertia, a sixth-order 40-h Butterworth low-pass 
filter (Roberts and Roberts, 1978) was applied to the 
raw volume transport to produce a net water transport 
(NWT). These net transport data effectively show the 
lower-frequency subtidal oscillations associated with 
atmospheric cold front events and other wind-forcing 
factors, and these data filter out the higher-frequency 
diurnal tidal oscillations (Li et al., 2009). 
Laboratory methods 
In the laboratory, ichthyoplankton collections with a 
volume of material greater than 200 mL were divided 
in half with a Motodo plankton splitter (Motodo Plank- 
ton Splitter, Aquatic Research Instruments, Hope, ID 
83836), and those collections with a volume greater 
than 400 mL were split into quarters. Samples were 
sorted under a dissecting stereoscope, and all ichthy- 
oplankton were removed. A subset of sorted samples 
was checked for completeness of ichthyoplankton re- 
moval by a second party and sorted again if necessary. 
Ichthyoplankton were identified to the lowest taxo- 
nomic level possible, depending on size and physical 
condition of each organism. Some larval fishes that 
were difficult to identify were stained with Alizarin 
blue and Alizarin red to facilitate meristic counts. At- 
lantic croaker larvae and early juveniles (hereafter 
referred to as larvae for brevity) were separated and 
stored for otolith analysis. Identifications were based 
on literature from Fahay (1983), and Richards (2006). 
Atlantic croaker larvae were subsampled for otolith 
analysis on the basis of a normal distribution of stan- 
dard length (SL) of all specimens collected. Measure- 
ment of SL to the nearest 0.1 mm was conducted with 
a Leica MZ6 stereoscope (Leica Microsystems Inc., Buf- 
falo Grove, IL) calibrated against a stage micrometer. 
Atlantic croaker larvae were sampled from every collec- 
tion that contained this target species. For samples in 
which 3 or less Atlantic croaker larvae were collected, 
all larvae of this species were scheduled for otolith re- 
moval. For samples that contained more than 3 larvae 
of Atlantic croaker, 3 larvae, specifically the shortest 
and longest specimens, along with one that was closest 
to the mean SL for all Atlantic croaker in the sample, 
were selected and scheduled for otolith removal. 
Otolith removal, preparation, and age interpretation 
Removal and preparation of sagittal otoliths from At- 
lantic croaker larvae selected for dissection followed 
