230 
Abstract — Gillnet mesh selectivity 
parameters were estimated for juve- 
nile blacktip sharks ( Carcharhinus 
limbatus) by using length data from 
an experimental fishery-independent 
gillnet survey in the northeastern 
Gulf of Mexico. Length data for 1720 
blacktip sharks were collected over 17 
years (1994-2010) with seven mesh 
sizes ranging from 7.6 to 20.3 cm. 
Four selectivity models, a normal 
model assuming fixed spread, a 
normal model assuming that spread 
is proportional to mesh size, a log- 
normal model, and a gamma model 
were fitted to the data by using the 
SELECT (share each length’s catch 
total) method. Each model was run 
twice under separate assumptions 
of 1) equal fishing intensity; and 2) 
fishing intensity proportional to mesh 
size. The normal, fixed-spread selec- 
tivity curve where fishing intensity is 
assumed to be proportional to mesh 
size provided the best fit to the data 
according to model deviance estimates 
and was chosen as the best model. 
Results indicate that juvenile blacktip 
sharks are susceptible as bycatch in 
some commercial gillnet fisheries. 
Manuscript submitted 23 March 2011. 
Manuscript accepted 23 December 2011. 
Fish. Bull. 110:230-241 (2012). 
The views and opinions expressed 
or implied in this article are those of the 
author (or authors) and do not necessarily 
reflect the position of the National Marine 
Fisheries Service, NOAA. 
Gillnet selectivity for juvenile blacktip sharks 
( Carcharhinus limbatus ) 
Ivy E. Baremore (contact author ) 1 
Dana M. Bethea 1 
Kate I. Andrews 2 
Email address for contact author: Ivy. Baremore (Sjnoaa.qov 
1 Panama City Laboratory 
Southeast Fisheries Science Center 
National Marine Fisheries Service 
National Oceanic and Atmospheric Administration 
3500 Delwood Beach Rd 
Panama City, Florida 32408 
2 Beaufort Laboratory 
Southeast Fisheries Science Center 
National Marine Fisheries Service 
National Oceanic and Atmospheric Administration 
101 Pivers Island Road 
Beaufort, North Carolina 28516-9722 
In the late 1980s, a gillnet fishery 
for sharks developed in the Atlantic 
Ocean off the coasts of Florida and 
Georgia (Trent et ah, 1997). Fishing 
area varied with seasons, and shark 
drift gillnet vessels operated in near- 
shore waters between 4.8 and 14.4 
km offshore, ranging from West Palm 
Beach, Florida (~26°46'N), to Alta- 
maha Sound, Georgia (~31°45'N). A 
variety of methods were used to deploy 
gillnets, including drifting the net on 
the surface (Trent et ah, 1997), strik- 
ing around a school of sharks (Carlson 
and Baremore 1 ), and anchoring the 
net to the bottom (Carlson and Bethea, 
2007). Fishermen targeted a variety of 
coastal species of sharks, from black- 
tip sharks (Carcharhinus limbatus) 
to Atlantic sharpnose sharks (Rhi- 
zoprionodon terraenouae ) depending 
on market conditions and fishery clo- 
sures. Over the last 10 years, the size 
and scope of the commercial shark 
gillnet fishery has decreased primar- 
1 Carlson, J. K., and I. E. Baremore. 
2003. The directed shark gillnet fish- 
ery: catch and bycatch 2003, NOAA Sus- 
tainable Fisheries Division Contribution 
PCB-03/07, 8 p. Panama City Labora- 
tory, National Marine Fisheries Service, 
Panama City, Florida. (Available from 
http://www.sefsc.noaa.gov/labs/panama/ 
documents/observer documents/gillnet/ 
SDG2003.pdf . accessed December 2011.] 
ily owing to regulations that restrict 
gear, fishing areas, and trip limits for 
sharks. In 2008, Amendment 2 to the 
Consolidated Atlantic Highly Migra- 
tory Species Fishery Management 
Plan (NMFS, 2008) limited landings 
of large coastal sharks to 33 sharks 
per trip. The high cost of fuel and 
low market value for shark meat, in 
conjunction with these regulations, 
caused most commercial fishermen 
in the U.S. south Atlantic Ocean to 
abandon the gillnet fishery for sharks. 
Although shark-targeted gillnet 
trips are currently rare in the U.S. 
Atlantic Ocean, blacktip sharks are 
still caught as bycatch in other gill- 
net fisheries that target species such 
as Spanish mackerel ( Scomberomorus 
maculatus ) and king mackerel (S. ca- 
valla) (Passerotti et ah, 2010; Thorpe 
and Frierson, 2009). These coastal 
teleost gillnet fisheries are expansive, 
and had more than 65 active fishing 
vessels in 2010. 2 The fishing locations 
of these vessels span the U.S. east 
coast throughout the range of the 
blacktip shark. 
The blacktip shark is a cosmopoli- 
tan species, ranging from Massachu- 
2 Southeast Fisheries Science Center 
Coastal Fisheries Logbook, available 
at http://www.sefsc.noaa.gov/fisheries/ 
reporting.htm . accessed March 2011. 
