Arendt et al.: Catch rates and demographics of Caretta caretta captured from the Charleston, South Carolina, shipping channel 
107 
primarily local sea turtles aggregate in shipping chan- 
nels each spring, coincident with some transient use. 
For example, a female loggerhead collected and tagged 
during this study nested on Cumberland Island, Geor- 
gia, two years later. Shipping channels in the southeast 
United States may also be important stops for juvenile 
loggerheads migrating between foraging and overwin- 
tering areas (Morreale, 1999; McClellan and Read, 
2007; Mansfield et al., 2009; Arendt et ah, in press). 
Juvenile female loggerheads were captured four times 
as frequently as males — a rate that is double that re- 
ported for pelagic juveniles collected from the Madeira 
Archipelago (Delgado et ah, 2010) and for neritic juve- 
niles from estuarine and coastal waters from Florida 
to North Carolina (Wibbels et al., 1991; Shoop et ah, 
1998; Braun-McNeill et ah, 2007). Sex ratios (two fe- 
males per male) reported for neritic loggerheads in U.S. 
waters also differ, however, from sex ratios determined 
by direct gonadal observation for (predominantly pelagic 
phase) loggerheads in the Mediterranean Sea, where 
a 1:1 ratio is reported (Casale et ah, 2006). Hopkins- 
Murphy et ah (2003) suggested that female-biased for- 
aging grounds may exist in the poorly surveyed tropics; 
however, fine-scale habitat partitioning by sex among 
juveniles within a geographic area is perplexing and 
to the best of our knowledge has not been previously 
reported. The four-to-one female bias for juvenile log- 
gerheads captured in this channel (the same ratio as 12 
females and three males of similar size collected from 
the same location between May and November 1991, 
NOAA 3 ) and higher injury rates among loggerheads 
collected from this channel than from adjacent shoals 
(Alderson, 2009) indicate that mortality of develop- 
ing females may disproportionately occur in shipping 
channels if the data reported here are representative 
of larger trends in the region. 
Conclusions 
Seasonal occurrence of loggerheads in shipping chan- 
nels and the distribution of shipping channels along a 
latitudinal gradient in the southeastern United States 
are ideal for assessing catch rates of loggerheads at 
a network of index sites, a high priority action of the 
Northwest Atlantic loggerhead recovery plan (NMFS 
and USFWS, 2008). Temporal and spatial variables 
appeared to exert the most influence on loggerhead catch 
rates and accounted for nearly half of model deviance in 
the present study. Within-channel spatial influences on 
catch in the present study were consistent with those 
from historic data and, as such, represent important 
sampling design considerations for future studies at 
3 NOAA (National Oceanographic and Atmospheric Administra- 
tion). Unpubl. data. Sex determination from testosterone 
radioimmunoassay conducted by David Owens, Texas A&M 
University. Data maintained by Kathy Moore, National 
Ocean Service, 219 Fort Johnson Road, Charleston, SC 29412, 
and available from Kathy.Moore@noaa.gov. 
this location, and likely at other shipping channels as 
well. Peak within-season catch in the present study con- 
trasted with monthly data reported for this location in 
1991 (Van Dolah and Maier, 1993) and 1992 (Dickerson 
et al. 1 ). Satellite telemetry data collected for a subset 
of loggerheads tagged and released during the present 
study revealed greatest affinity for adjacent shoals and 
fidelity to the channel itself during spring (Arendt et al., 
in press) — an affinity consistent with in situ tracking at 
this location during spring (Keinath et al. 4 ) and summer 
(Maier et al. 5 ). As such, there exists a high probability 
of being able to assess and account for “detectability” 
(Anderson, 2001) in shipping channels with spatial and 
temporal factors, which in turn should enhance the sta- 
tistical confidence of using shipping channels as index 
sites for long-term trends assessments. Fine-scale influ- 
ences on detectability of loggerheads within shipping 
channels will likely require continuous and concurrent 
monitoring of loggerhead occurrence and a suite of envi- 
ronmental variables and should be included in future 
research efforts to study sea turtle distributions in ship- 
ping channels. In addition to strengthening statistical 
confidence, such data sets could also potentially help 
identify mechanisms to reduce anthropogenic mortal- 
ity rates, which are a continued conservation need, and 
that were the original premise for evaluating sea turtle 
occurrence in shipping channels. 
Acknowledgments 
We thank the captains and crew of the RV Lady Lisa 
and the RV Georgia Bulldog, as well as numerous 
seasonal employees and volunteers for logistical sup- 
port. S. Epperly, S. Hopkins-Murphy, and anonymous 
reviewers provided editorial contributions, and J. Boyn- 
ton assisted with graphics. Funding was provided by 
the National Marine Fisheries Service, NOAA, grant 
NA03NMF4720281, and research was permitted under 
section 10(a)(1)(A) directed sea turtle permits #1245 
and #1540. This is contribution #684 of the Marine 
Resources Division of the South Carolina Department of 
Natural Resources and #368 of the College of Charles- 
ton’s Grice Marine Laboratory. 
4 Keinath, J. A., D. E. Barnard, and J. A. Musick. 1997. Behav- 
ior of loggerhead sea turtles in Savannah, Georgia, and 
Charleston, South Carolina, shipping channels. In Sea 
turtle research program summary report, p. 41-93. U.S. 
Army Corps of Engineers Waterways Experiment Station 
Technical Report CHL-97, 147 p. + appendices. U.S. [Avail- 
able from http://dodreports.com/pdf/ada332588.pdf, accessed 
June 2011.] 
5 Maier, P. P., A. L. Segars, M. D. Arendt, and J. D. Whita- 
ker. 2005. Examination of local movement and migratory 
behavior of sea turtles during spring and summer along the 
Atlantic coast off the southeastern United States. Annual 
Rept. to the Office of Protected Resources, National Marine 
Fisheries Service, NOAA. Grant Number NA03NMF4720281, 
29 p. [Available from http://www.sefsc.noaa.gov/turtledocs/ 
CR„Maier etal_2005_erratum.pdf , accessed June 2011.] 
