46 
Fishery Bulletin 11 7(1-2) 
for time-of-year in spawning interval and RBF analy¬ 
ses, despite evidence that these parameters may vary 
throughout the reproductive season (Fitzhugh et ah, 
2012b, Lowerre-Barbieri et ah, 2015). However, most 
studies commonly focused on reproductive sampling for 
these parameters during peak (summer) reproductive 
months, thus eliminating some temporal variation. 
Our analyses indicate there was an overall decrease 
in egg production between 1991 and 2017, a decrease 
in RBF, and either no change or an increase in spawn¬ 
ing interval. These differences were more pronounced 
in the northwestern GOM than in the northeastern 
GOM. Athough there was a downward trend in rela¬ 
tive batch fecundity for the northeast, no substan¬ 
tial changes were estimated. There was no change in 
spawning interval in the northeast, whereas an in¬ 
crease was seen in the northwest when the OM method 
was used to calculate spawning interval. The lack of a 
meaningful change in spawning interval values with 
the POF method was likely due to large variations in 
the spawning interval values across months. Fish with 
POFs were more infrequently captured at the begin¬ 
ning and ending of the reproductive season than fish 
undergoing OM, leading to smaller sample sizes. De¬ 
spite the duration of the spawning season remaining 
relatively constant from 1994 through 2017, a decrease 
in total egg production (lower RBF, greater spawning 
interval) suggests lower annual fecundity in the stock, 
particularly in the northwestern GOM. Our analyses 
suggest the potential of a compensatory reproductive 
effect may be more evident in the northwestern GOM. 
This compensatory effect may correspond with stock 
assessment projections of higher levels of spawning 
stock biomass and a greater likelihood of sustained re¬ 
covery in the west (Cass-Calay et al., 2015, SEDAR 52, 
2018), resulting in increased fish density and greater 
competition for resources as discussed above. 
Differences in the population structure of red snap¬ 
per stocks between the eastern and western GOM 
have been previously identified. The northwestern 
GOM shows evidence of greater numbers of older red 
snapper, particularly in the last 8-10 years (Saari et 
al., 2014, Cass-Calay et al., 2015, Porch et al., 2015, 
Karnauskas et al., 2017, SEDAR 52, 2018), as well as 
greater numbers of eggs and larvae (Lyczkowki-Shultz 
and Hanisko, 2007, Hanisko et al., 2017). There is 
also evidence of a metapopulation structure of north¬ 
ern GOM red snapper; the demographic differences 
between GOM regions are supported by genetic analy¬ 
sis (Gold and Saillant, 2007, Puritz et al., 2016). Pre¬ 
vious findings of differences in maturity, growth, and 
demographics between the eastern and western GOM 
have suggested that density-dependent processes may 
be occurring (Fitzhugh et al., 2004, Jackson et al., 
2007, Saari et al., 2014). Kulaw et al. (2017) recently 
reported more evidence of regional differences in com¬ 
paring reproductive traits from Alabama and Louisiana 
red snapper sampled ~10 years apart, and again in¬ 
voked compensation to help explain these differences. 
As with the present study, they saw a decreased trend 
in spawning frequency (increased spawning interval) 
and provided evidence for decreased GSI and increas¬ 
ing age at maturity in their northwestern GOM study 
area. Kulaw et al. (2017) reported that a more detect¬ 
able trend of declining reproductive output was evi¬ 
dent among younger females in the west than in the 
east of the Mississippi River. However, Kulaw et al. 
(2017) tempered their conclusions regarding the degree 
of density dependence by age because of their limited 
sample size, and pointed to potential habitat factors in 
partially explaining their results. 
Red snapper are most commonly found associated 
with underwater structures, and the type of structure 
(i.e., habitat) may influence reproduction. Higher re¬ 
productive output was found at natural versus artifi¬ 
cial habitats on the outer Louisiana shelf area of study 
(Glenn et al., 2017, Kulaw et al., 2017), although natu¬ 
ral and artificial reefs were at different depths which 
may confound the reported results. Red snapper in¬ 
habiting deep (60-100 m) artificial reefs have a longer 
spawning season and a higher percentage of spawn¬ 
ing-capable and actively spawning females than red 
snapper at shallow (<20 m) reefs (Brown-Peterson and 
Moncrief 2 ); these differences are likely related to larger 
fish captured at deeper depths. In contrast, differences 
in reproductive parameters were not seen among habi¬ 
tats in artificial and natural reefs in the same depth 
zone off Texas (Downey et al., 2018). High densities of 
young red snapper are particularly common on artifi¬ 
cial structures, such as oil platforms and small artifi¬ 
cial reefs, although these structures represent only a 
fraction of the area in the northern GOM (Karnauskas 
et al., 2017). The majority of the data since 2012 used 
in the analyses in the present study have been from 
artificial structures. Therefore, we cannot reject the 
possibility that age and habitat may be confounding 
influences in our results, but we examined red snapper 
from a wider geographic area and longer time period 
than those of previous studies. 
Although we were unable to model regional dif¬ 
ferences in spawning seasonality, it is clear from our 
analysis that the peak spawning time for red snapper 
in the northern GOM of June through August has re¬ 
mained relatively constant over the 27-year period ex¬ 
amined. This peak spawning period is well supported 
in the literature (Render, 1995; Collins et al., 1996; 
Fitzhugh et al., 2004). Our analysis suggests May is 
also a peak spawning month since 1994, which is cor¬ 
roborated by back calculated spawning dates of juve¬ 
nile red snapper in 1995 (Szedlmayer and Conti, 1999). 
In addition, spawning capable female red snapper have 
been recently reported from April, September, and ear¬ 
ly October (Lowerre-Barbieri et al., 2012; Fitzhugh et 
al., 2012a). Our model used mean monthly GSI > 1.0 
2 Brown-Peterson, N. J., and T. D. Moncrief. 2017. Does 
depth influence Red Snapper reproductive biology metrics? 
In Abstract book, 2017 Joint Meetings of Ichthyologists and 
Herpetologists, Austin, Texas, p. 69-70. Available from 
website. 
