410 
Fishery Bulletin 1 10(4) 
Table 5 
Estimated age and time that cobia (Rachycentron canadum ) eggs from plankton collections were spawned in Port Royal Sound 
(PRS) and St. Helena Sound (SHS), South Carolina, in 2008. Estimated spawning time is rounded down to the nearest quarter 
hour. Station codes: PA=PRS anchored net; SA=SHS anchored net; numbers correspond to a specific station. 
Sample pick-up Estimated time of spawning 
Station 
Date 
Time 
Age of eggs (hr) 
Date 
Time 
SA01 
5/21/2008 
1816 
19.5 
5/20/2008 
2045 
SA02 
5/21/2008 
1835 
21.5 
5/20/2008 
2100 
SA03 
5/21/2008 
1850 
21.5 
5/20/2008 
2115 
SA06 
5/21/2008 
1920 
21.5 
5/20/2008 
2145 
SA01 
5/28/2008 
1237 
19.5 
5/27/2008 
1700 
SA03 
5/28/2009 
1304 
19.5 
5/27/2008 
1730 
PA07 
5/29/2008 
1350 
21.5 
5/28/2008 
1615 
PA08 
5/29/2008 
1405 
21.5 
5/28/2008 
1630 
PA09 
5/29/2008 
1425 
21.5 
5/28/2008 
1700 
SA01 
6/3/2008 
1827 
25.5 
6/2/2008 
1700 
SA02 
6/3/2008 
1850 
25.5 
6/2/2008 
1720 
SA03 
6/3/2008 
1900 
25.5 
6/2/2008 
1730 
SA06 
6/3/2008 
1923 
25.5 
6/2/2008 
1800 
PA07 
6/5/2008 
1912 
26.0 
6/4/2008 
1715 
PA08 
6/5/2008 
1927 
2-3 
6/5/2008 
1630-1730 
1927 
26.0 
6/4/2008 
1730 
PA07 
6/12/2008 
1255 
20.0 
6/11/2008 
1700 
PA08 
6/12/2008 
1303 
21.5 
6/11/2008 
1530 
SA03 
6/18/2008 
1757 
24.0 
6/17/2008 
1800 
Conclusions 
On the basis of the evidence provided here, cobia 
spawn in PRS and SHS during May and June. The 
collection of cobia eggs in early stages of development, 
the high average inshore GSI values, and the presence 
of actively spawning females in PRS and SHS makes 
this study the first one to positively document spawn- 
ing of cobia in inshore waters. Spawning occurs in the 
afternoon and evening (primarily between 1530 and 
1800 hr), as indicated by the embryological develop- 
ment of eggs and aging of wild-caught eggs. Some 
studies have suggested daytime and evening spawn- 
ing of cobia based on the reported observation of what 
was believed to be spawning activity of adult cobia 
(see Shaffer and Nakamura, 1989), developmental 
stage of wild caught cobia eggs (Ditty and Shaw, 
1992), and volitional spawning of a single female cobia 
held in captivity (Weirich et al., 2006); however, we 
documented daytime and evening spawning through 
multiple methods. 
Intense recreational fishing can produce changes 
in fish populations and communities in ways similar 
to the effects of commercial fishing (Coleman et al., 
2004; Cooke and Cowx, 2006). Moreover, hyperstability 
may mask overfishing conditions (Sadovy and Domeier, 
2005), whereby catches remain constant at spawning 
aggregations as stocks decline, as observed in species 
such as the orange roughy ( Hoplostethus atlanticus) 
(Clark et al., 2000; Koslow et al., 2000) and Nassau 
grouper ( Epinephelus striatus ) (Sala et al., 2001). Co- 
bia found on the Atlantic coast of the United States 
were considered to be overfished by the SAFMC and 
GMFMC 3 in 1983, although the only assessment of 
the cobia fishery was conducted in the Gulf of Mexico 
(Williams, 2001). Since 1983, cobia has gained popu- 
larity among recreational anglers, as evidenced by the 
continual increase in effort by South Carolina charter 
boats since 1997 (Steele 4 ). 
Additional research needs to be conducted to deter- 
mine the contribution of fish that spawn inshore to 
the overall U.S. Atlantic population of cobia because 
spawning may occur offshore as well, as hypothesized 
in other studies (Hassler and Rainville, 1975; Smith, 
1996; Burns et al. 1 ). Documentation of spawning in 
PRS and SHS indicates that inshore waters elsewhere 
in their region may also provide critical habitat for 
cobia. Together, the documented spawning and the 
discovery of a unique population segment within South 
Carolina inshore waters (Darden 4 ) provide compel- 
ling reasons for management agencies to reconsider 
current management strategies. To treat all cobia in 
U.S. waters as a single population may no longer be 
appropriate, and the possible existence of regional, 
self-sustaining population segments should be taken 
into account. 
