14 
Fishery Bulletin 110(1) 
Mississippi-Alabama-Florida shelf— Spring 
ctj 
CL 
Water depth ( m) 
Figure 6 
Partial effects [s(covariate); y-axis] of the generalized additive model (GAM) for 
each covariate (x-axis) used in the best subregion by season GAM of percent fre- 
quency of occurrence (%FO) of grouper larvae (all taxa combined) collected during 
Southeast Area Monitoring and Assessment Program spring sampling (April-May, 
1986-2005) in the Mississippi-Alabama-northern Florida subregion. Modeled par- 
tial effects (solid lines) and 95% confidence intervals (dotted lines) are shown for 
each included covariate. The dark dashed line marks no effect. Percent frequency 
of occurrence was higher for partial effects greater than 0, and lower for values 
less than 0. Vertical dashes along the x-axis denote actual sample values for the 
covariate. ****P<0.001, ***P<0.01, **P< 0.05. 
likely cause the observed increase in fall-spawned 
grouper larvae in the years since 1995. 
Discussion 
Seasonal occurrence 
Larval grouper seasonality, as defined by the occurrence 
of larvae in collections from the Straits of Florida, relates 
directly to spawning season. Spawning likely occurs 
approximately one month (average pelagic larval dura- 
tion <45 days; Colin et ah, 1997; Lindemann et ah, 2000; 
Fitzhugh et al., 2005) before occurrence of postflexion- 
stage larvae, and within two weeks of the occurrence of 
preflexion-stage larvae (Glamuzina et al., 2000; Leu et 
al., 2005). Because larvae were generally collected at the 
beginning of each month during collections in the Straits 
of Florida, actual spawning could have occurred in the 
month before collection. Although larvae were collected 
year-round, most larvae were collected during early 
February and March (Table 4) — a period that would 
correspond with a January through March spawning 
season. This is generally considered the primary spawn- 
ing season of most northwest Atlantic groupers (Collins 
et al., 1998; Johnson et al., 1998; Brule et al., 2003; 
Nemeth et al., 2007; Starr et al., 2007). A second period 
of high larval species richness was observed during 
early September and October, indicative of spawn- 
ing from August to October (Table 4; Bullock et al., 
1996; Sadovy and Eklund, 1999; Richards et al., 2005). 
Analysis of larval seasonal occurrence indicated lon- 
ger spawning seasons than those identified in studies 
of adult groupers. Graysby are considered fall spawners 
throughout their range (Richards et al., 2005), and most 
graysby larvae were collected during July-October in 
shallow shelf waters on the west Florida Shelf (mean 
depth of 49.2 m vs. >60 m for all other taxa). However, 
