Driggers et al.: Distribution of Squatinidae in waters of the western North Atlantic Ocean 
345 
peratures in relatively shallow waters of the Dry Tor- 
tugas and Florida Keys are in excess of 24°C (Lee and 
Williams, 1999),—temperatures above the preferred 
temperature range for angel sharks. Therefore, if an¬ 
gel sharks do occur in shallow waters of the eastern 
GOM, the relatively high water temperatures of the 
Dry Tortugas and Florida Keys year-round could act 
as a barrier for angel shark movement into the Straits 
of Florida. To our knowledge, the only record of angel 
sharks occurring in shallow waters of the eastern GOM 
is attributable to Fowler (1906) who stated that local 
fishermen reported Rhina squatina (a junior synonym 
for S. dumeril ) was “occasionally taken in summer” in 
the Florida Keys. Because of the morphological simi¬ 
larity between angel sharks and guitar fishes (Rhino- 
bat id ae) and because the Atlantic guitarfish ( Pseudo- 
batos lentiginosus) is “often encountered in shallow 
waters around the Florida Keys” (Bigelow and Schro- 
eder, 1953), we believe Fowler’s (1906) report of angel 
sharks occurring in the area to be in error. 
South of the Dry Tortugas, the South Florida Es¬ 
carpment is within the preferred depth range for angel 
sharks and could represent a relatively narrow corridor 
through which angel sharks could move from the GOM 
into the Florida Straits. Additionally, based on our data 
(Fig. 6) and on visual inspection of temperature data 
presented by Soto (1985), bottom temperature on the 
South Florida Escarpment at depths between approxi¬ 
mately 150 and 250 m is within the preferred tempera¬ 
ture range of angel sharks during a portion of the year. 
However, Longley and Hildebrand (1941) did not list 
angel sharks among the fishes collected in dredges con¬ 
ducted across the South Florida Escarpment, south of 
the Dry Tortugas, and on the Tortugas Terrace, despite 
having documented other shark species, such as the 
chain dogfish ( Scyliorhinus retifer ) and Caribbean lan- 
ternshark (Etmopterus hillianus). Additional sampling 
will be required to determine whether angel sharks 
are present within the Straits of Florida, particularly 
along the South Florida Escarpment and on the Pour- 
tales Terrace where bottom temperatures are within 
the preferred range of this species. 
Velocity and direction of the Florida Current as 
it moves through the Straits of Florida and chang¬ 
es trajectory to the north off the southeastern tip of 
Florida are other possible mechanisms acting, possi¬ 
bly in concert with temperature, to limit movements 
of angel sharks between the EC and GOM. Although 
information on the swimming performance of Atlan¬ 
tic angel sharks is scant, Standora and Nelson (1977) 
examined the diel activity patterns of Pacific angel 
sharks (S. californica) associated with Santa Catalina 
Island, California. The authors concluded the species 
is relatively sedentary during daylight hours and be¬ 
comes more active at night. Mean sustained swimming 
speeds during nocturnal periods were approximately 
11 cm/s and maximum reported sustained swimming 
speed was approximately 25 cm/s. Lee et al. (1992) de¬ 
ployed an acoustic Doppler current profiler to a depth 
of 200 m in the Straits of Florida south of Looe Reef 
and recorded bottom currents up to 40 cm/s. Hamilton 
et al. (2005) analyzed data from buoy arrays moored off 
Jupiter in southeastern Florida and reported current 
speeds of over 70 cm/s at a depth of 300 m. Relatively 
high bottom current speeds and seasonal bottom cur¬ 
rent reversals (e.g., Diiing and Johnson, 1972), coupled 
with the comparatively low maximum sustained swim¬ 
ming speed of angel sharks, could make the Straits of 
Florida energetically demanding to traverse and thus a 
potential barrier for exchange between basins. 
Unlike angel sharks off the EC, angel sharks were 
not collected inshore in the GOM during fishery-in- 
dependent surveys despite extensive sampling efforts 
in shallow waters. However, of the 60,827 commer¬ 
cial shrimp trawl catches sampled by fishery observ¬ 
ers from 1981 through 2015 in the GOM from January 
to April, angel sharks were observed in 9 trawls con¬ 
ducted at depths less than 70 m (Hart 6 ). Furthermore, 
an experienced commercial shark fisherman provided 
photographs of an angel shark captured in nearshore 
waters of the northern GOM during the winter of 2018 
and reported frequent captures of angel sharks in gill 
nets off Mississippi and Alabama at depths as shallow 
as 18 m during winter months of January and Febru¬ 
ary (Stiller 7 ). Therefore, more sampling will be needed 
in the northern GOM during winter months to fully de¬ 
scribe seasonal variability in the depth range of angel 
sharks within the region. 
Angel sharks were collected throughout the north¬ 
ern GOM. However, in an area off Louisiana, between 
the Mississippi River Delta and the western edge of 
Mississippi Canyon, only 2 individuals were collected 
over the 67-year sampling period, despite 3600 trawls 
conducted in that area during that period. This hypoth¬ 
esized discontinuity in distribution could be related to 
a number of factors, including the steepness of the 
narrow shelf at the terminus of the Mississippi Delta, 
upwelling of cold water through the Mississippi Can¬ 
yon, or abiotic conditions related to discharge from the 
Mississippi River. A similar discontinuity in the distri¬ 
bution and genetic population structure of blacknose 
sharks ( Carcharhinus acronotus ) associated with the 
same area was identified by Portnoy et al. (2014) using 
molecular techniques. The authors speculated that the 
freshwater plume associated with the Mississippi River 
potentially acts as a physiological barrier between the 
eastern and western GOM for stenohaline species. Like 
blacknose sharks, angel sharks in the GOM appear to 
be stenohaline because they were collected in a nar¬ 
row range of preferred salinity (i.e., 34.7-36.3). Future 
research will be needed to address the discontinuity in 
distribution in this region and whether it is related to 
salinity. 
6 Hart. R. 2016. Unpubl. data. Southeast Fish. Sci. Cent., 
Natl. Mar. Fish. Serv., NOAA, 4700 Ave. U, Bldg. 306, 
Galveston, TX 77551. 
7 Stiller, D. 2018. Personal commun. Commercial fisher¬ 
man. 
