Kolmos et al.: Temporal changes in the life history of Hyporthodus niveatus off North and South Carolina 
315 
Age (years) 
Figure 3 
The von Bertalanffy growth curves for snowy grouper 
(.Hyporthodus niveatus) captured off North and South Car¬ 
olina during 3 periods: 1982-1985, 1993-1994, and 2008- 
2012. Ages are counts of annual increments from otolith 
readings. The asterisk (*) above each line denotes the old¬ 
est fish aged for that period. n=number of fish examined. 
Table 4 
Mean estimates of parameters of the von Bertalanffy 
growth function, the theoretical maximum length (LJ), 
growth coefficient (k), and initial condition parameter (t 0 ), 
for snowy grouper (Hyporthodus niveatus ) collected off 
North and South Carolina during 3 periods: 1982-1985, 
1993-1994, and 2008-2012. Data were combined for 3 gear 
types: Kali pole, long bottom longline, and short bottom 
longline. n=number of fish examined; SE=standard error 
of the mean. 
Period n SE k SE t 0 SE 
1980s 169 1004 47 0.085 0.015 -3.44 1.03 
1990s 1215 1115 12 0.120 0.004 -1.37 0.12 
2000s 1383 1090 10 0.119 0.004 -0.95 0.12 
All periods 2767 980 5 0.126 0.003 -1.85 0.13 
potential spawning season is from late January through 
early October. 
Spawning activity varied by size and age. An anal¬ 
ysis of spawning proportion in relation to TL revealed 
that there was less spawning in the smallest fish (501- 
GOO mm TL), with this length bin having the lowest pro¬ 
portion of spawners (0.06), a generally shorter spawning 
season (2-5 weeks), and the smallest number of batches 
(8) compared with those of larger fish (Table 6). Spawn¬ 
ing proportion and number of batches increased with fish 
length, reaching the maximum values of 0.18 in the bin 
for fish >901 mm TL and 27 batches in the bin for fish 
801-900 mm TL. There was a slight decrease to 24 batches 
at lengths >901 mm TL, possibly because of the shorter 
spawning season in this size class. For all length bins, 
the lowest spawning proportions occurred at the begin¬ 
ning (April) and end (September) of the spawning season 
(Fig. 7A). In addition, the positive relationship between 
spawning proportion and fish length was evident through¬ 
out the spawning season. 
Analyses also were completed on effects of age on spawn¬ 
ing proportion (Table 7). The youngest snowy grouper (ages 
3-4) had the lowest proportion of spawners (0.03), with the 
proportion increasing to 0.11 at ages 5-6 and leveling out 
to 0.14—0.15 at ages >6 years. Because the spawning sea¬ 
son also is shorter at younger ages, spawning frequency 
similarly increased, from 15 batches at ages 5-6 to 22-24 
batches at older ages; the number of batches for ages 3-4 
could not be calculated as a result of the small sample size. 
Spawning interval decreased slightly with age, from 9 d 
at ages 5-6 to 7 d at older ages. Similar to results from 
analyses of the length data, a general pattern of the lowest 
values of spawning proportion occurring at the beginning 
(April) and end (September) of the spawning season was 
observed for snowy grouper at ages >5 years (Fig. 7B). In 
the youngest age bin (3-4 years), spawners were captured 
only in July. 
Spawning patterns indicate a lunar periodicity 
(GAM: n=371; test: 91.3, P<0.001). Overall, the GAM 
explained 26.7% of the deviance in spawning probabil¬ 
ity (coefficient of multiple determination [P 2 ] =0.312). 
On the basis of occurrence of spawners, spawning was 
least likely to occur around the full moon period (lunar 
days 15-18), whereas most spawning occurred between 
the waning crescent and waxing crescent phases, with a 
peak during the period of the new moon (lunar days 0-3 
and 22-28) (Fig. 8). No adult female fish were collected 
on lunar days 6-8. 
Discussion 
The results of analyses of life history parameters sup¬ 
port the conclusion of the most recent stock assessment 
that the population of snowy grouper off North and South 
Carolina has started a slow recovery from an overfished 
status: spawning stock biomass (SSB) is less than SSB at 
maximum sustainable yield (MSY). Results from analyses 
of age and growth, sex composition, and maturity all indi¬ 
cate a positive response to regulations to reduce fishing 
effort (i.e., further reductions in trip limit and annual 
quota for commercial sector) that were implemented after 
the previous assessment (SEDAR, 2013). Wyanski et al. 
(2000) proposed that the plasticity observed in growth 
between the early 1980s and the period 1993-1994 repre¬ 
sented a density-dependent response to an increase in 
fishing mortality. Given that regulations implemented 
since 1994, and especially since 2006, have reduced fishing 
mortality, examination of life history samples collected 
