28 
Fishery Bulletin 1 14(1) 
Table 2 
Average growth rates (mm/d) and instantaneous growth rates (G) for larval and 
early juvenile Atlantic croaker ( Micropogonias undulatus ) collected in Bayou Tartel- 
lan, Louisiana, based on otolith data grouped by age blocks of 10 days after hatching 
(dah). Rates are provided for 2 sampling years — October 2006 through March 2007 
and September 2007 through March 2008 — and for the overall combined data. 
Blocks (dah) 
2006-2007 
2007-2008 
Overall 
(mm/d) 
G 
(mm/d) 
G 
(mm/d) 
G 
0-10 
0.115 
0.057 
0.138 
0.065 
0.124 
0.060 
10-20 
0.152 
0.045 
0.175 
0.048 
0.161 
0.046 
20-30 
0.181 
0.036 
0.193 
0.035 
0.187 
0.036 
30-40 
0.198 
0.029 
0.190 
0.025 
0.196 
0.027 
40-50 
0.203 
0.023 
0.173 
0.019 
0.192 
0.021 
50-60 
0.198 
0.018 
0.149 
0.014 
0.178 
0.016 
60-70 
0.185 
0.014 
0.122 
0.010 
0.158 
0.013 
indicating a more protracted spawning season (Barb- 
ieri et al., 1994a). The second peak in hatching dates 
in late January and early February for both sampling 
years indicates a possible second spawning subgroup 
(Fig. 6; Warlen, 1980; Thorrold et al., 1997). Warmer 
water temperatures during winter sampling efforts in 
year 2 were very similar to temperatures during the 
fall months in sampling year 1, potentially explaining 
the protracted spawning season in 2007-2008 (Lank- 
ford and Targett, 2001a, 2001b; Hare and Able, 2007). 
Growth rates of larval and early juvenile Atlantic 
croaker collected in Bayou Tartellan increased and be- 
came variable after larvae encountered lower-salinity 
(<20) coastal boundary and estuarine waters, as did 
growth rates for Atlantic croaker when entering estua- 
rine waters along the MAB (Nixon and Jones, 1997). 
The growth rate of 0.20 mm/d from the linear model 
in our study compares favorably with the growth rate 
of 0.19 mm/d documented from larvae collected from 
inner continental shelf waters offshore of Sabine Pass, 
Texas, and the Mermentau River, Louisiana (Cowan, 
1988). The instantaneous maximum growth rates from 
the Laird-Gompertz model for the fall and spring of 
both sampling years fell within the range of growth 
rates reported for coastal waters off North Carolina; 
0.16-0.27 mm/d (Warlen, 1980). The differences in sea- 
sonal growth rates within the Laird-Gompertz models 
provide evidence of spawning and recruitment sub- 
groups with maximum growth rates occurring 20 dah 
later in the fall than in the spring — a finding indicat- 
ing that the larvae spend a longer time period in a 
more productive and potentially more suitable essen- 
tial fish habitat during the spring (Searcy et al., 2007; 
Sponaugle, 2010). Similar subgroups also have been 
observed in North Carolina waters (Warlen, 1980) and 
the MAB (Thorrold et al., 1997), where seasonal differ- 
ences in growth rates were a result of food availability 
and variation in salinity. 
The differences in seasonal growth rates observed 
in our study, however, may also be partially explained 
by the movement of spawning fish farther inshore as 
the season progressed (Barbieri et al., 1994a, 1994b), 
thereby shortening their time within the recruitment 
corridor when transiting to estuarine nursery grounds 
and more favorable growth conditions. Lower salinities 
(<15) indicative of estuarine waters have been shown 
to increase somatic growth rates of larval Atlantic 
croaker (Peterson et al., 1999). Although all analyses 
of growth in our study revealed similar growth rates, 
the use of the Laird-Gompertz model allowed more ac- 
curate hindcasting of the low growth rates of larvae in 
the recruitment corridor on the continental shelf be- 
cause we used model true estimates of hatching length, 
and the linear models failed to accurately reflect or ac- 
count for length at hatching. 
The mean age of larval Atlantic croaker that trans- 
gressed the lower-salinity (<20) waters of the coastal 
boundary layer and entered the estuary was estimated 
to be approximately 40 dah, on the basis of changes in 
otolith ring width and distance of the ring from the core 
(Fig. 6, A and B). Ontogenetic change in otolith shape 
did not affect ring width or distance from the core be- 
cause all otoliths in our study were roughly circular. 
Studies of ingress into Chesapeake Bay, Delaware Bay, 
and Pamlico Sound have shown ages at time of ingress 
to be between 30 and 60 dah (Warlen, 1980; Miller et 
al., 2003; Schaffler et al., 2009a, 2009b), a range that 
compares favorably with the results from direct aging 
of larvae collected for our study in the Bayou Tartellan 
tidal pass: between 22 and 70 dah. 
The role of periodic atmospheric winter frontal 
passages on densities of larval Atlantic croaker has 
been shown to be significant in this system (Kupchik, 
2014), indicating that patterns such as inlet geomor- 
phology and wind-forcing factors can play a large role 
in the timing of ingress for Atlantic croaker (Raynie 
