OCCURRENCE OF TIGER SHARK (GALEOCERDO
CUVIER) SCAVENGING ON AVIAN PREY AND ITS
POSSIBLE CONNECTION TO LARGE-SCALE BIRD
DIE-OFFS IN THE FLORIDA KEYS
A. J. GALLAGHER(1,2)*, T. JACKSON(4),
(1)
AND
N. HAMMERSCHLAG(1,2,3)
Leonard and Jayne Abess Center for Ecosystem Science and Policy, University of Miami,
P.O. Box 248203, Coral Gables, FL 33124, USA
(2)
RJ Dunlap Marine Conservation Program, University of Miami, 4600 Rickenbacker Causeway,
Miami, FL 33149, USA
(3)
Rosenstiel School of Marine and Atmospheric Science, University of Miami, 4600 Rickenbacker
Causeway, Miami, FL 33149, USA
(4)
NOAA Fisheries, Southeast Fisheries Science Center, 75 Virginia Beach Drive,
Miami, FL 33149, USA
Biological Sciences
OCCURRENCE OF TIGER SHARK (GALEOCERDO
CUVIER) SCAVENGING ON AVIAN PREY AND ITS
POSSIBLE CONNECTION TO LARGE-SCALE BIRD
DIE-OFFS IN THE FLORIDA KEYS
A. J. GALLAGHER(1,2)*, T. JACKSON(4),
AND
N. HAMMERSCHLAG(1,2,3)
(1)
Leonard and Jayne Abess Center for Ecosystem Science and Policy, University of Miami,
P.O. Box 248203, Coral Gables, FL 33124, USA
(2)
RJ Dunlap Marine Conservation Program, University of Miami, 4600 Rickenbacker Causeway,
Miami, FL 33149, USA
(3)
Rosenstiel School of Marine and Atmospheric Science, University of Miami, 4600 Rickenbacker
Causeway, Miami, FL 33149, USA
(4)
NOAA Fisheries, Southeast Fisheries Science Center, 75 Virginia Beach Drive,
Miami, FL 33149, USA
ABSTRACT: The tiger shark, Galeocerdo cuvier, is the largest predatory fish in tropical waters.
Due to its wide-ranging movements, diverse diet and perceived potential threat to humans, the feeding
behavior of this species has received significant attention in the scientific literature for over 40 years.
Such studies have identified various prey items and feeding strategies for tiger sharks worldwide, and
new insights into the life-history (i.e. movement, diet, reproduction) of this currently threatened
predator are useful in conservation and management initiatives. Here we describe observations of tiger
shark scavenging on a terrestrial avian species off the Florida Keys and its potential connection to
several large-scale bird die-offs within the region.
Key Words:
bird, movement, diet, elasmobranch, conservation
THE tiger shark (Galeocerdo cuvier) is a large semi-coastal/oceanic species,
which populates temperate and tropical waters (Compagno, 2005). Due to its
wide-ranging diet, the tiger shark has long been regarded as a generalist
predator in various ecosystems (e.g., Springer, 1960; DeCrosta et al., 1984;
Lowe et al.; 1996). Studies assessing the dietary breadth of tiger sharks have
identified several prey items, with the most commonly consumed being teleost
fishes, marine reptiles, marine mammals, and sea birds (Heithaus, 2001;
Simpfendorfer et al., 2001; Meyer et al., 2010). Additionally, the discovery of
foreign, non-digestible items inside tiger shark stomachs has further supported
this predator’s reputation as an opportunistic forager/scavenger (Linaweaver
and Backus, 1969; Lowe, 1996). While there is a wealth of studies describing
tiger shark life history characteristics such as diet, the most descriptive
accounts of such have been conducted in the Indian and the Pacific Oceans
* Corresponding author email: [email protected]
264
No. 4 2011]
GALLAGHER ET AL.—TIGER SHARK DIET
265
(e.g., Simpfendorfer et al., 1992; Heithaus, 2001; Heithaus et al., 2002;
Papastamatiou et al., 2006).
Here we describe a rare observation involving a tiger shark scavenging on a
terrestrial species of avian prey in the Atlantic Ocean. We combine movement
data collected from the satellite-tagged tiger shark to examine the scavenging
event in relation to various large-scale bird die-offs in the Florida Keys.
MATERIALS AND METHODS—As part of a larger study on the abundance and life histories of
large coastal sharks in the subtropical Atlantic, we initiated a satellite tagging study of tiger sharks
off the Florida Keys (USA). Sharks were captured using baited drumlines as described by
Hammerschlag et al. (2011). Drumlines were deployed for 1 h before being checked for shark
presence. On November 13, 2010, we captured a 255 cm (TL 5 total length) female tiger shark in
US federal waters, off the reef edge in the middle Florida Keys (N 24.69, W 80.85). While gathering
tissue samples and taking measurements, the shark regurgitated a large collection of partially
digested primary and secondary contour feathers held together by shorn ligaments and digestive
juices (Figure 1A). The regurgitated specimen was immediately frozen and brought back to the
laboratory for later identification. Prior to release, the shark’s dorsal fin was affixed with a SPOT5
satellite tag to provide high-resolution information on its migratory behavior, providing
geolocation data each time tag breaks the surface. Over the next two weeks, the tiger shark
moved approximately 200 km in a northerly direction, displacing a tight affinity for the southeast
coastline of Florida (Figure 2).
The avian specimen was photographed and sent to various specialists and bird experts. Tom
Webber, Bird Collection Manager of the Florida Museum of Natural History, positively identified
the specimen as the left wing from an American Coot (Fulica americana; Tom Webber, pers comm;
Figure 1B). In addition to positive photographic identification, the physical specimen was similarly
identified as a coot by a staff of veterinarians specializing in avian rehabilitation from the Miami
Museum of Science (S. Montgomery and G. Mealey, pers comm.).
DISCUSSION—Birds have previously been documented as a prey item of
tiger sharks in the Pacific (e.g., Papastamatiou et al., 2006; Whitney et al.,
2007). For example, off Hawaii, tiger sharks instinctively forage on juvenile
fledging albatross at the French Frigate Shoals (e.g., Lowe et al., 1996). Our
observation, although just one event, is relatively rare and provides additional
evidence for tiger shark and bird predator-prey interactions in the Atlantic
Ocean. To our knowledge, there have been only four previous scientific reports
describing avian remains in the stomachs of tiger sharks in the Atlantic Ocean,
this being the second documented occurrence of a terrestrial avian prey eaten
by a tiger shark (Gudger, 1949; Saunders and Clarke, 1962; Dodrill and
Gilmore, 1978; Carlson et al., 2002). All previous reports have discovered
feathers and bones from terrestrial and other marine birds through stomach
dissection. In this study, the tiger shark regurgitated an American Coot, a
freshwater swimming rallid that is found in temperate wetlands and marsh
systems across the Southeastern North America (Brisbin et al., 2002). The
regurgitation and non-digested status of this prey item may signify recent
consumption due to the early stages of physical and chemical digestion.
Three days prior to our observation reported here, forty large birds were
discovered floating dead, moribund, or stressed in the waters of Biscayne Bay,
Florida (N 25.59, W 80.26, marked ‘‘X’’ in Figure 2). The mass of birds
266
FLORIDA SCIENTIST
[VOL. 74
FIG. 1. (A) Largely undigested remnants of a left wing of an American Coot, regurgitated
from our 255 cm tiger shark. (B) American coot wing from the Bird Collection of the Florida
Museum of Natural History (photo: Tom Webber).
No. 4 2011]
GALLAGHER ET AL.—TIGER SHARK DIET
267
FIG. 2. Two-week movement path from our satellite tagged shark starting on November 13,
2010 (marked with star). Location of initial bird die-off also noted.
included turkey vultures (Carthartes aura), hawks (Buteo spp.) and American
Coot (Fulica Americana; Florida Keys Wild Bird Center). Satellite-tag data
from this tiger shark show a direct northerly movement past the region where
the above bird die-off occurred, followed by several highly tortuous
movements in a restricted area from Ft. Lauderdale to Miami (Figure 2).
These types of convoluted, back-and-forth movements of sharks have been
previously thought to occur in response to areas of high resource availability
and/or a change in habitat quality (Sims et al., 2006; Weng et al., 2008).
Moreover, any scavenging by tiger sharks on dead or moribund floating birds
would occur at the surface. It is likely that the deposit and outflow of the
strong uropygial and sensory cues emitted from the mass of dead and/or dying
birds could change the movement of local marine predators and attract sharks
(acute sensory predators) to opportunistically scavenge on the birds. Interestingly, over the next 10 days, an estimated 400–500 additional terrestrial bird
carcasses were also found floating in the waters of Florida Bay and Everglades
National Park (V. Nograd, pers. comm.). These locations are within close
268
FLORIDA SCIENTIST
[VOL. 74
temporal and spatial proximity to where we observed the tiger shark
regurgitate the American Coot.
While not in any way decisive, it is plausible that the tiger shark we tagged
may have encountered the bird die-off, scavenged, then moved back north, a
scenario corroborated by our satellite tagging data, time-window and locations
of the die-off events, and home range of tiger sharks in this region (Authors,
unpublished data). While the causes of these bird die-offs still remain nebulous,
pathogenic infection has been suggested as a potential driver. Accordingly,
such a mass transfer of disease into marine food webs could be a cause for
environmental and ecosystem-level concern.
ACKNOWLEDGEMENTS—We thank the interns and staff of the RJ Dunlap Marine Conservation
Program for their ongoing field support, as well as C. Slonim, C. Hammerschlag-Peyer, S.
Genovese, J. Serafy and K. Broad, G. Maranto from the Abess Center. For bird information and
assistance with specimen identification, we also thank the NOAA Southeast Fisheries Center, T.
Curtis, T. Webber from the Florida Museum of Natural History, S. Montgomery and G. Mealey of
the Miami Museum of Science, and V. Nograd of the Florida Keys Wild Bird Center.
LITERATURE CITED
BRISBIN, I. L. JR., H. D. PRATT, AND T. B. MOWBRAY. 2002. American Coot (Fulica americana) and
Hawaiian Coot (F. alai). The Birds of North America. No. 697.
CARLSON, J. K., M. A. GRACE, AND P. K. LAGO. 2002. An observation of juvenile tiger sharks
feeding on clapper rails off the southeastern Coast of the United States. Southeast. Nat.
1:307–310.
COMPAGNO, L. J. V., M. DANDO, AND S. FOWLER. 2005. Sharks of the World, Collins Field Guide.
Harper Collins Publishers, London, 368 pp.
DECROSTA, M. A., L. R. TAYOR JR. AND J. D. PARRISH. 1984. Age determination, growth, and
energetics of three species of carcharhinid sharks in Hawaii, in Proceedings of the Second
Symposium on Resource Investigations in the Northwest Hawaiian Islands, Vol. 2, May 25–
27, 1983. University of Hawaii Sea Grant MR-84-01, pp. 75–95.
DODRILL, J. W. AND G. R. GILMORE. 1978. Land birds in the stomachs of tiger sharks Galeocerdo
cuvieri (Peron and Leseur). Auk. 95:585–586.
GUDGER, E. W. 1949. Natural history notes on tiger sharks, Galeocerdo tigrinus, caught at Key
West, Florida, with emphasis on food and feeding habits. Copeia. 1949:39–47.
HAMMERSCHLAG, N., A. J. GALLAGHER, AND D. M. LAZARRE. 2011. A review of shark satellite
tagging studies. Journal of Exp. Mar. Biol. and Ecol.
HEITHAUS, M. R. 2001. The biology of tiger sharks, Galeocerdo cuvier, in Shark Bay, Western
Australia: sex ratio, size distribution, diet, and seasonal changes in catch rates. Environ.
Biol. Fish. 61:25–36.
———, L. M. DILL, G. J. MARSHALL, AND B. BUHLEIER. 2002. Habitat use and foraging behavior of
tiger sharks (Galeocerdo cuvier) in a seagrass ecosystem. Mar. Biol. 140:237–248.
LINAWEAVER, T. H. III AND R. H. BACKUS. 1969. The natural history of sharks. Doubleday and Co.
Inc, Garden City, New York. 293 pp.
LOWE, C. G., B. M. WETHERBEE, G. L. CROW, AND A. L. TESTER. 1996. Ontogenetic dietary shifts
and feeding behavior of the tiger shark, Galeocerdo cuvier, in Hawaiian waters. Environ.
Biol. Fish. 47:203–211.
MEYER, C. G., Y. P. PAPASTAMATIOU, AND K. N. HOLLAND. 2010. A multiple instrument approach
to quantifying the movement patterns and habitat use of Tiger (Galeocerdo cuvier) and
Galapagos sharks (Carcharhinus galapagensis) at French Frigate Shoals, Hawaii. Mar. Biol.
157:1857–1868.
No. 4 2011]
GALLAGHER ET AL.—TIGER SHARK DIET
269
PAPASTAMATIOU, Y. P., B. M. WETHERBEE, C. G. LOWE, AND G. L. CROW. 2006. Distribution and
diet of four species of Carcharhinid shark in the Hawaiian Islands: evidence for resource
partitioning and competitive exclusion. Mar. Ecol. Prog. Ser. 320:239–251.
SAUNDERS, G. B. AND E. CLARK. 1962. Yellow-billed cuckoo in stomach of tiger shark. Auk. 79:118.
SIMPFENDORFER, C. A. 1992. Biology of tiger sharks (Galeocerdo cuvier) caught by the Queensland
shark meshing program off Townsville, Australia. Aust. J. Mar. Freshwater Res. 43:33–43.
———, A. B. GOODREID, AND R. B. MCCAULEY. 2001. Size, sex and geographic variation in the diet
of the tiger shark, Galeocerdo cuvier, from Western Australian waters. Environ. Biol. Fish.
61:37–46.
SIMS, D. W., M. J. WITT, A. J. RICHARDSON, E. J. SOUTHALL, AND J. D. METCALFE. 2006. Encounter
success of free-ranging marine predator movements across a dynamic prey landscape. Proc.
R. Soc., B. 273(1591):1195–1201.
SPRINGER, S. 1960. Natural history of the sandbar shark, Eulamnia milberti. US Fish Bull. 61:1–38.
WENG, K. C., D. G. FOLEY, J. E. GANONG, C. PERLE, G. L. SCHILLINGER, AND B. A. BLOCK. 2008.
Migration of an upper-level trophic predator, the salmon shark, Lamna ditropis, between
distant ecoregions. Mar. Ecol. Prog. Ser. 372:253–264.
WHITNEY, N. M. AND G. C. CROW. 2007. Reproductive biology of the tiger shark (Galeocerdo
cuvier) in Hawaii. Mar Biol. 151:63–70.
Florida Scient. 74(4): 264–269. 2011
Accepted: June 21, 2011
Florida Academy of Sciences. 2011
E