Kupchik and Shaw: Age, growth, and recruitment of larval and early juvenile Micropogonias undulatus 
29 
0.10 - 
0.08 - 
Fall— Year 1 
Fall— Year 2 
Spring — Year 1 
Spring — Year 2 
Estuarine Ingress 
0.06 - 
0.04 - 
0.02 
0.00 
_ • , e. 
:; ;X 
*»•.****•*•■■ 
k# 
10 
20 
30 
40 
50 
60 
70 
Age (dah) 
0.0035 
B 
0.0030 
0.0025 
1 0.0020 
0.0015 
0.0010 
0.0005 - 
0.0000 
10 20 30 40 50 
Age (dah) 
60 70 
Figure 6 
(A) Mean distance of the ring from the core, which serves as 
a proxy for growth, by season for otoliths of larval and early 
juvenile Atlantic croaker (Micropogonias undulatus) sampled in 
Bayou Tartellan, Louisiana, during 2006-2008. Data for fall of 
year 1 (2006), fall of year 2 (2007), spring of year 1 (2007), and 
spring of year 2 (2008) are provided to show differences between 
year and season, and the dashed line demarcates the estimated 
average ingress date. (B) Mean ring width for individual daily 
rings from imaged otoliths. 
and Shaw, 1994; Joyeaux, 1998; Wood, 2000). 
Larval ingress can be driven by active mecha- 
nisms like selective tidal stream transport, but 
the vertically well-mixed nature of tidal passes 
in the northern GOM and particularly in our 
sampling site of Bayou Tartellan indicates that 
the driving forces are passive mechanisms of 
recruitment and retention, such as residual 
bottom flow (Joyeux, 1999; Schultz et al., 2003), 
wind-driven transport (Shaw et ah, 1985; Jo- 
yeaux, 1999; Hare et ah, 1999; Hare and Gov- 
oni, 2005), or flow differentials across channels 
due to boundary conditions and marsh edge ef- 
fects (Lyczkowski-Shultz et al., 1990; Raynie, 
1991; Raynie and Shaw, 1994; Kupchik, 2014). 
Growth rates for Atlantic croaker larvae 
collected in water masses with salinities and 
temperatures consistent with continental shelf 
waters were lower than growth rates for larvae 
collected in water masses with characteristics 
associated with estuarine or coastal boundary 
waters. The effect of salinity on growth rate 
is further exemplified by the steep increase in 
growth rate during ebb tides, which bring low 
salinities indicative of waters from the upper 
estuarine nursery ground. Increased growth 
associated with lower salinities has been docu- 
mented previously for larval Atlantic croak- 
er in other estuaries (Peterson et al., 1999). 
Growth rate as a function of water tempera- 
ture showed no difference associated with tide. 
Higher growth rates were associated with low- 
er water temperatures, and those rates proba- 
bly reflected the increased productivity of estu- 
aries, which, during late fall and winter, have 
cooler temperatures and lower salinities than 
the warmer, more saline waters of the GOM. 
The notable exception to this pattern was the 
increase in growth rate that occurred during 
positive NWTs associated with flood tides, and 
this increase in growth rate may be a func- 
tion of interim or prefrontal conditions associ- 
ated with southerly winds and higher coastal 
sea level in relation to the reestablishment of 
the tidal prism after flushing from northerly 
winds of the postfrontal phase. Results from 
the mixed model confirmed the importance of 
salinity for growth of larval and juvenile At- 
lantic croaker that has been noted in previous 
studies (Sogard, 1992; Rooker and Holt, 1997; 
Lankford and Targett, 2001a) and the temporal 
and spatial variability that has been associated 
with differences between estuarine and conti- 
nental shelf waters (Searcy et al., 2007). 
Analysis of digital images of daily rings in 
saccular otoliths of larval Atlantic croaker, col- 
lected in Bayou Tartellan from October 2006 
through March 2007 and from September 2007 
through March 2008, provided a fast, reliable 
method for analyzing otolith rings, growth rate, 
