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2007 SOUTHEASTERN NATURALIST 6(1):183–186
Occurrence of Carcharhinus isodon (Finetooth Shark) in
Tonya R. Wiley1,* and Colin A. Simpfendorfer1
Abstract - Carcharhinus isodon (finetooth shark) is a migratory shark found in
coastal waters of the southeastern United States and is well documented in the waters
of north Florida in both the Gulf of Mexico and the Atlantic Ocean. The southernmost
reports are from Lemon Bay (27°N), just north of Charlotte Harbor on the west
coast and from Port Salerno (27°N) on the east coast. Four C. isodon were captured
on bottom-set longline in Florida Bay, just north of 25°N latitude, during routine
sampling for Pristis pectinata (smalltooth sawfish). These captures extend the southern
range of C. isodon in Florida to approximately 25ºN and increase the likelihood
of exchange between the Atlantic and Gulf stocks.
Carcharhinus isodon Müller and Henle (finetooth shark) is a moderate-
sized species of shark found in shallow US coastal waters from North
Carolina to Florida and in the northern Gulf of Mexico (Bethea et al.
2004, Carlson et al. 2003, Castro 1993). Compagno (1988) reported C.
isodon occur from New York south to Florida, and from Cuba in the Gulf
of Mexico to Texas and Mexico, also Guyana and southern Brazil. Castro
(1983) described the species as inhabiting the Atlantic coast of North
America from New York to Florida and the Gulf of Mexico.
Carcharhinus isodon inhabits the western Atlantic from North Carolina
to Brazil and is common off the southeastern United States, where it
spends the summer off Georgia and the Carolinas and winters off Florida
(Castro 1993). The species is known to migrate southward in early fall as
the water temperatures decrease (Carlson and Brusher 1999, Castro
1993). There are few records from the Caribbean and south Atlantic and
no valid records of this species from Cuba (Castro 1993). In Florida, C.
isodon have been reported in the Florida panhandle (Bethea et al. 2004,
Carlson et al. 2003), Port Salerno (Springer 1950), Lemon Bay (Clark and
von Schmidt 1965), Melbourne Beach (Dodrill 1977), and Daytona Beach
(Castro 1993). Therefore, the range of C. isodon has been documented as
north of 27°N, the latitude of Port Salerno on the Atlantic coast and
Lemon Bay on the Gulf of Mexico coast. However, the capture of four
specimens just north of 25°N in Florida Bay represents an extension to
the southern range of this species in the United States.
1Mote Marine Laboratory, Center for Shark Research, 1600 Ken Thompson Parkway,
Sarasota, FL 34236. *Corresponding author - firstname.lastname@example.org.
184 Southeastern Naturalist Vol. 6, No. 1
Longline sets targeting P. pectinata, have been carried out since 2000 from
Tampa Bay to the outer Florida Keys. Longlines consisted of an 800-m
bottom-set mainline of 8-mm braided nylon rope anchored and marked with
buoys at each end. Gangions were constructed of 1 m of 5-mm braided nylon
cord and 1 m of stainless steel wire leader. Mustad tuna circle hooks (12/0 to
16/0) were baited with frozen Mugil cepahlus Linnaeus or M. curema
Valenciennes (mullet). The date, time, and location of each set were recorded.
Physical parameters (water temperature, salinity, and dissolved oxygen) were
recorded at each sampling location midway between the surface and bottom
using a YSI 85 water-quality meter.
Sharks caught during surveys were identified and sexed. Four measurements
of length to the nearest 0.5 cm were taken when possible: precaudal
(PCL), fork (FL), total (TL) and stretched total length (STL). Locations of
longline sets and C. isodon captures were plotted using a geographic information
system (ArcView 3.3).
During 1233 longline sets from Tampa Bay to Key West, four C. isodon
were captured in Florida Bay (Fig. 1). Three were captured on 12 February
Figure 1. Locations of 1233 longline sets (x), three Carcharhinus isodon captured 12
February 2003 (A), and one captured 10 February 2005 (B).
2007 T.R. Wiley and C.A. Simpfendorfer 185
2003 just south of East Cape Canal (25°7'24"N, 80°3'59"W) and the fourth
on 10 February 2005 near Curry Key (25°7'54"N, 80°57'48"W) west of
Flamingo. The first three were caught at a depth of 1.3 m and the fourth at
1.1 m. Despite extensive year-round sampling, the four C. isodon were all
captured in February in water temperatures of 22.2 and 23.5°C. The two
male C. isodon were 111 and 130 cm TL, and the two females were 115 and
estimated 100 cm TL.
The water temperatures and timing of the C. isodon captures was consistent
with Castro's (1993) reporting that they leave the Carolinas in early fall
and migrate southward as the surface water temperature decreases below
20°C. Dodrill (1977) reported the species to be found off Melbourne Beach
from November to April. Similarly, Carlson and Brusher (2004) reported
that young of the year and juveniles remain in Apalachicola Bay, in the
Florida Panhandle, until fall, when they emigrate offshore into the Gulf of
Mexico. It is unknown if the four C. isodon captured in Florida Bay are from
the Gulf of Mexico or Atlantic Ocean populations; however, the timing of
the captures coincides with the southward winter migration of
Given that differences in reproductive biology have been reported between
C. isodon occurring in the Atlantic and Gulf of Mexico, it is possible
that there is little or no interaction between these two stocks. Castro (1993)
reports males reach maturity at about 130 cm and females at 135 cm TL for
animals from the Atlantic Ocean. Carlson et al. (2003) reported males reach
maturity between 100 and 129 cm TL and females between 118 to 124 cm
TL in the northern Gulf of Mexico. This separation of the Atlantic and Gulf
stocks may be mediated with thermal preference, which restricts this species
from reaching the Florida Keys where interaction may occur. The occurrence
in Florida Bay at the southern tip of Florida increases the likelihood
that there is greater movement or interaction between these two stocks than
indicated by previous information on their distribution.
The results of this finding extend the southern range of C. isodon in
Florida to approximately 25ºN and increase the likelihood of exchange
between the Atlantic and Gulf stocks. The low level of catch, despite
extensive sampling in southwest Florida, suggests that their incidence in
southern Florida is rare and only occurs when water temperatures are low
during winter. Further research on the movements of this species, both in the
Gulf of Mexico and along the Atlantic coast will be required to understand
the seasonal movement patterns and extent of their southern movements.
We thank J. Castro for help with C. isodon reports and distribution. Funding
from NOAA Fisheries Office of Protected Resources, National Fish and Wildlife
186 Southeastern Naturalist Vol. 6, No. 1
Foundation, National Geographic Committee for Research and Exploration, The
Disney Wildlife Conservation Fund, and Florida Fish and Wildlife Conservation
Commission supported this research.
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