OCCURRENCE OF TIGER SHARK (GALEOCERDOCUVIER) SCAVENGING ON AVIAN PREY AND ITSPOSSIBLE 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

Biological Sciences

OCCURRENCE OF TIGER SHARK (GALEOCERDOCUVIER) SCAVENGING ON AVIAN PREY AND ITSPOSSIBLE 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: agallagher@rsmas.miami.edu

264

(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

No. 4 2011] GALLAGHER ET AL.—TIGER SHARK DIET 265

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).

266 FLORIDA SCIENTIST [VOL. 74

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. Intere-

stingly, 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

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.

No. 4 2011] GALLAGHER ET AL.—TIGER SHARK DIET 267

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 taggedmay 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.

268 FLORIDA SCIENTIST [VOL. 74

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

E Florida Academy of Sciences. 2011

No. 4 2011] GALLAGHER ET AL.—TIGER SHARK DIET 269