A Loggerhead Sea Turtle (Caretta Caretta) Preying on Fish Within a Mixed Species Feeding Aggregation...

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A Loggerhead Sea Turtle (Caretta caretta) Preying on Fish Within a Mixed-Species

Feeding Aggregation

Author(s): Shigetomo Hirama and Blair Witherington

Source: Chelonian Conservation and Biology, 11(2):261-265. 2012.

Published By: Chelonian Research Foundation

DOI: http://dx.doi.org/10.2744/CCB-0918a.1

URL: http://www.bioone.org/doi/full/10.2744/CCB-0918a.1

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Chelonian Conservation and Biology, 2012, 11(2): 261–265g 2012 Chelonian Research Foundation

A Loggerhead Sea Turtle (Caretta caretta)

Preying on Fish Within a Mixed-Species

Feeding Aggregation

SHIGETOMO HIRAMA1

AND BLAIR WITHERINGTON1

1Florida Fish and Wildlife Conservation Commission, 9700 South

A1A, Melbourne Beach, Florida 32951 USA [[email protected];

[email protected]]

ABSTRACT. – Loggerhead sea turtles (Caretta caretta)

feed predominantly on marine crustaceans, mollusks,

and other hard-shelled macroinvertebrates. In this

note, we report on a subadult loggerhead observed to

be feeding on live fish swarming around the turtle in a

prey-fish ball. The observation suggests that logger-

heads occasionally prey upon certain pelagic fish

species other than those encountered as carrion or

fishing bait, and may explain accounts of turtles

impaled by billfish (Istiophoridae) rostra.

Loggerhead sea turtles (Caretta caretta) inhabit

tropical, subtropical, and temperate waters worldwide.

As they become large immature and adult turtles,

loggerheads occupy predominantly benthic habitats in

neritic waters (Bolten 2003). In Florida (USA) logger-

heads forage within coastal inlets (Butler et al. 1987),

lagoons (Ehrhart et al. 2007), bays (Lutcavage and

Musick 1985; Schroeder and Foley 1995), and on

deepwater (.

10-m–deep) offshore reefs (Girard et al.2009) in the Gulf of Mexico and Atlantic Ocean. Due to

difficulties associated with offshore research, loggerhead

foraging in habitats distant from land is not well studied

relative to foraging in coastal habitats. When loggerhead

diet has been described in the literature, the information

has come principally from analyses of gut contents in

shore-stranded turtles.

Gut contents of stranded loggerheads have included

predominantly marine crustaceans, mollusks, and other

hard-shelled macroinvertebrates (Lutcavage and Musick

1985; Dodd 1988; Ruckdeschel and Shoop 1988; Burke

and Standora 1993; Plotkin et al. 1993; Lazar et al. 2010).

In addition to these naturally occurring prey items, longlinefishing baits (Revelles et al. 2007) and discarded fish

(White 2004) have also been recorded from loggerhead gut

contents.

Given their apparent preference for slow-moving

prey and their limited capacity for rapid movement (S.

Hirama and B. Witherington, pers. obs.), loggerheads

would not be expected to eat live, fast-moving pelagic

fishes. However, many pelagic fishes form compact, ball-

shaped schools that may change their vulnerability to

predation (Pitcher and Parrish 1993). A prey-fish ‘‘ball’’

NOTES AND FIELD REPORTS 261



typically contains small fish close to the water’s surface

(Marchal and Lebourges 1996). The schooling of these

prey fish is thought to confuse predators and increase prey

survivorship (Partridge 1982; Milinski 1984; Magurran and

Pitcher 1987). In the present article, we describe a

loggerhead sea turtle that was a focal point

of a prey-fish ball, allowing the turtle to feed on the

constituent fish.Observation Note. — On 30 July 2009, at approxi-

mately 1900 hrs, we were returning to port after

conducting offshore vessel transects for oceanic juvenile

sea turtles in the northern Gulf of Mexico. Approximately

26 km from shore, lat 29u259040N, long 85u059440W,

in water 18 m deep, we observed a large immature

loggerhead (approximately 70-cm straight carapace

length) at the surface (Fig. 1). Above the turtle, seabirds

in a mixed-species flock were diving and feeding on fish.

The seabird species included black terns (Chlidonias

niger , Fig. 1D), Audubon’s shearwaters (Puffinus lhermi-

nieri), royal terns (Thalasseus maximus, Fig. 1C), and

sandwich terns (Thalasseus sandvicensis, Fig. 1D). As weapproached the feeding site, we observed that the seabirds

were feeding on fish swimming out from water and onto

the loggerhead’s partially exposed carapace (Fig. 1A).

We recorded a series of 114 images with a Canon single

lens reflex camera with a 400-mm focal length, f5.6

telephoto lens. Approximately 20 m from the turtle, we

entered the water to observe the loggerhead from beneath

the surface. Upon reaching the turtle, we recorded 82

images with a Canon Power Shot A710IS camera within

an underwater housing. From our observations and

recorded images, we noted that the school of prey fish

was in a compact spherical ball similar to that described

in the literature (Clua and Grosvalet 2001), except that aturtle was at its center (Fig. 2). We observed 6 species of

fish near the loggerhead. The prey fish aggregation

consisted of 3 species, round scad ( Decapterus punctatus;

Carangidae) and sardines ( Harengula jaguana and

Sardinella aurita; Clupeidae). We observed that predator

fish, little tunnies (Euthynnus alletteratus), were congre-

gating and striking from below in order to feed on the

prey fish at the perimeter of the ball. We also observed

five sharksuckers (Echeneis sp.) circling and occasionally

attaching to the turtle, and lesser amberjacks (Seriola

fasciata) also maneuvering tightly around the turtle. The

loggerhead repeatedly made lateral head movements with

its mouth held open. On at least 3 occasions, the turtle

closed its mouth on a fish that had swum between its jaws,

allowing the turtle to crush the fish and swallow it. These

consumed fish could not be specifically identified, but

were one of the 3 prey species, Decapterus punctatus,

Harengula jaguana, and Sardinella aurita.

Discussion. — Schools of prey fish decrease their

surface-area-to-volume ratio by forming a ball swarm,

and further limit their exposure to fish predators by

swarming near the water’s surface. However, this surface

concentration made the prey fish we observed susceptible

to predation by seabirds. Seabirds commonly associate

with dolphins and tunas, and in oceanic waters these birds

may rely on prey fish available at the surface because of

these subsurface predators (Ashmole and Ashmole 1967;

Au and Pitman 1986). We hypothesize that the prey-fish

school we observed received additional antipredator

advantages in being sheltered by the loggerhead. The

presence of the turtle likely prevented the approach of predators from the side of the school occupied by the

turtle, and when at the center of the ball, the loggerhead

likely prevented predators from striking through the

school. In our observed case, although the prey fish

may have benefitted from their proximity to the turtle, a

trade-off was predation by the turtle.

Direct observations of loggerheads feeding on food

items in the wild are rare. Although there are some first-

hand records of interactions between loggerheads and

their prey (e.g., Sauls and Thompson 1994), most

information on loggerhead foraging comes from ex post

facto examination of ingested items. One might infer that

most fish found in loggerhead digestive tracts were deadwhen eaten, given that most fish can easily escape the

sluggish movements limiting a loggerhead’s predatory

capacity (Shoop and Ruckdeschel 1982; Lutcavage and

Musick 1985). For example, Plotkin et al. (1993) inferred

that fish parts found in the digestive tract of stranded

loggerheads were from fish eaten as carrion because the

guts also contained large numbers of the scavenging

gastropod Nassarius acutus. Seney and Musick (2007)

found Atlantic menhaden ( Brevoortia tyrannus), Atlantic

croaker ( Micropogonias undulatus), striped bass ( Morone

saxatilis), bluefish (Pomatomus saltatrix), and seatrout

(Cynoscion sp.) in digestive tracts of loggerheads. These

authors reasoned that most of these fish had been fed uponas they were either alive or freshly dead, having been

restrained or killed by commercial fishing nets. A low

frequency of scavenging mud snails in the gut contents

supported this observation. In contrast, Revelles et al.

(2007) were unable to explain the origins of clupeid fish,

which were the highest-frequency item in digestive tracts

from 19 dead loggerheads in the western Mediterranean.

Tomas et al. (2001) found that teleost fishes were the

principal constituent within gut contents of 54 logger-

heads captured by trawls in the western Mediterranean.

The ingested fish included 13 species, including two

clupeids (Sardina pilchardusa and Alosa alosa). The

authors concluded that the clupeids had been discarded

bycatch, but that the short-snouted seahorse ( Hippocam-

pus hippocampus), a slower-moving benthic fish also

found in some of the turtle stomachs, may have been

consumed alive (Tomas et al. 2001).

One question about loggerhead feeding behavior

concerns the extent to which they are opportunistic

feeders or are selective of targeted food items (Dodd

1988). Although we do not present a sample sufficiently

large to answer this question, we do offer an observation

of opportunistic feeding on live prey fish in which a

262 CHELONIAN CONSERVATION AND BIOLOGY, Volume 11, Number 2 – 2012



Figure 1. A surfacing subadult Caretta caretta, with Decapterus punctatus, Harengula jaguana, Sardinella aurita, and Seriola fasciata swimming close to the turtle’s carapace (A, B), and Thalasseus maximus (C), Thalasseus sandvicensis, and Chlidonias niger (D) flying over prey fish.

Figure 2. Underwater images of a subadult Caretta caretta with Decapterus punctatus, Harengula jaguana, Sardinella aurita,Echeneis sp., and Euthynnus alletteratus.




loggerhead exhibited predatory behavior that would not

seem to be effective in feeding on its more commonly

encountered benthic prey species. In the loggerhead we

observed, success in capturing prey fish seemed to be

linked to the swarming tactic used by the prey fish, a

tactic presumed to reduce predation by larger fish. We

propose prey-ball feeding as an explanation for the

occurrence of tightly schooling pelagic fish in loggerheaddiet samples.

It remains unclear how commonly prey-fish school

around loggerheads, but we point to additional observa-

tions that could be explained by these events, such as

interactions between billfishes (Istiophoridae) and sea

turtles. Frazier et al. (1994) describe four confirmed

cases of turtles (loggerhead; olive ridley, Lepidochelys

olivacea; leatherback, Dermochelys coriacea; green

turtle, Chelonia mydas) being impaled by billfish rostra.

In their interpretation, the authors concluded that the

interactions may have occurred incidentally due to prey

fish (the billfishes’ target species) congregating around

the turtles.We suggest two areas of caution in drawing conclu-

sions from fish found in the gut contents of loggerhead sea

turtles. One is that certain pelagic fish species may

occasionally be preyed upon while alive and are not

always encountered as carrion or fishing bait. A second

caution is that researchers are probably correct in

identifying other fishes found in loggerhead diet samples

to be the result of net-catch, discarded bycatch, or fishing

bait, especially if there is additional supporting evidence.

ACKNOWLEDGMENTS

The observation was made during work funded by

grant NA09NMF4720040 from the NOAA, National

Marine Fisheries Service (NMFS), and by Florida’s

Marine Resources Conservation Trust Fund. Work was

carried out under a NMFS Permit for Scientific Purposes

under the Endangered Species Act (permit 14726). The

authors are grateful to D. Adams and E. Matheson for their

comments and assistance with fish identification. We

thank J. Boyett, B. Crowder, A. Foley, R. Hardy, A.

Meylan, and T. O’Meara for providing comments on the

manuscript.

LITERATURE CITED

ASHMOLE, N.P. AND ASHMOLE, M.J. 1967. Comparative feeding

ecology of sea birds of a tropical oceanic island. Peabody

Museum of Natural History, Yale University, Bulletin 24.

New Haven, CT: Peabody Museum of Natural History.

AU, D.W.K. AND PITMAN, R.L. 1986. Seabird interactions with

dolphins and tuna in the eastern tropical Pacific. Condor 88:

304–317.

BOLTEN, A. 2003. Variation in sea turtle life history patterns:

neritic vs. oceanic developmental stages. In: Lutz, P.L.,

Musick, J.A., and Wyneken, J. (Eds.). The Biology of Sea

Turtles, Volume II. Boca Raton, FL: CRC Press Inc, pp. 243–

257.

BURKE, V. AND STANDORA, E. 1993. Factors affecting strandings

of cold-stunned juvenile Kemp’s Ridley and loggerhead sea

turtles in Long Island, New York. Copeia 4:1136–1138.

BUTLER, R., NELSON, W., AND HENWOOD, T. 1987. A trawl survey

method for estimating loggerhead turtle, Caretta caretta,

abundance in five eastern Florida channels and inlets. US

National Marine Fisheries Service Fishery Bulletin 85(3):

447–453.

CLUA, E. AND GROSVALET, F. 2001. Mixed-species feeding

aggregation of dolphins, large tunas and seabirds in the

Azores. Aquatic Living Resources 14:11–18.

DODD, C. 1988. Synopsis of the Biological Data on the

Loggerhead Sea Turtle Caretta caretta (Linnaeus 1758). US

Fish and Wildlife Service Biological Report 88(14),

110 pp.

EHRHART, L., REDFOOT, W., A ND BAGLEY, D. 2007. Marine turtles

of the central region of the Indian River Lagoon System,

Florida. Florida Scientist 70(4):415–434.

FRAZIER, J.G., FIERSTINE, H.L., BEAVERS, S.C., ACHAVAL, F.,

SUGANUMA, H., PITMAN, R.L., YAMAGUCHI, Y., AND PRIGIONI,

C.M. 1994. Impalement of marine turtles (Reptilia, Chelonia:

Cheloniidae and Dermochelyidae) by billfishes (Osteichthyes,

Perciformes: Istiophoridae and Xiphiidae). Environmental

Biology of Fish 39:85–96.GIRARD, C., TUCKER, A., AND CALMETTES, B. 2009. Post-nesting

migrations of loggerhead sea turtles in the Gulf of Mexico:

dispersal in highly dynamic conditions. Marine Biology

156(9):1827–1839.

LAZAR, B., GRACAN, R., K ATIC, J., ZAVODNIK , D., JAKLIN, A., AND

TVRTKOVIC, N. 2010. Loggerhead sea turtles (Caretta caretta)

as bioturbators in neritic habitats: an insight through the

analysis of benthic molluscs in the diet. Marine Ecology 32:

65–74.

LUTCAVAGE, M. AND M USICK , J. 1985. Aspects of the biology of

sea turtles in Virginia. Copeia 2:449–456.

MAGURRAN, A. AND PITCHER, T. 1987. Provenance, shoal size

and the sociobiology of predator-evasion behaviour in

minnow shoals. Proceedings of Royal Society B229(1257):

439–465.

MARCHAL, E. AND LEBOURGES, A. 1996. Acoustic evidence for

unusual diel behaviour of a mesopelagic fish (Vinciguerria

nimbaria) exploited by tuna. Journal of Marine Science 53:

443–447.

MILINSKI, M. 1984. A predator’s costs of overcoming the

confusion-effect of swarming prey. Animal Behaviour 32(4):

1157–1162.

PARTRIDGE, B. 1982. Structure and function of fish schools.

Scientific American 246(6):90–99.

PITCHER, T.J. AND PARRISH, J.K. 1993. Functions of shoaling

behaviour in teleosts. In: Pitcher, T.J. (Ed.). Behaviour of

Teleost Fishes. New York: Chapman and Hall, pp. 363–

439.

PLOTKIN, P., WICKSTEN, M., AND AMOS, A. 1993. Feeding ecologyof the loggerhead sea turtle, Caretta caretta, in the

northwestern Gulf of Mexico. Marine Biology 115:1–15.

REVELLES, M., CARDONA, L., AGUILAR, A., AND FERNANDEZ, G.

2007. The diet of pelagic loggerhead sea turtles (Caretta

caretta) off the Balearic archipelago (western Mediterra-

nean): relevance of long-line baits. Journal of the Marine

Biological Association of the United Kingdom 87:805–813.

RUCKDESCHEL, C. AND SHOOP, C. 1988. Gut contents of

loggerheads: findings, problems, and new questions. In:

Schroeder, B.A. (Comp.). Proceedings of the Eighth Annual

Workshop on Sea Turtle Biology and Conservation. NOAA

Technical Memorandum NMFS-SEFC-214:97–98.

264 CHELONIAN CONSERVATION AND BIOLOGY, Volume 11, Number 2 – 2012



SAULS, B. AND THOMPSON, M. 1994. Observations of a

loggerhead turtle feeding in the wild. Marine Turtle

Newsletter 67:28–29.

SCHROEDER, B. AND FOLEY, A. 1995. Population studies of marine

turtles in Florida Bay. In: Richardson, J.I. and Richardson,

T.H. (Comps.). Proceedings of the Twelfth Annual Workshop

on Sea Turtle Biology and Conservation; NOAA Technical

Memorandum NMFS-SEFSC-361 274, pp. 117

SENEY, E. AND MUSICK , J. 2007. Historical diet analysis of loggerhead sea turtles (Caretta caretta) in Virginia. Copeia 2:

478–489.

SHOOP, C. AND RUCKDESCHEL, C. 1982. Increasing turtle

strandings in the southeast United States: a complicating

factor. Biological Conservation 23(3):213–215.

TOMAS, J., AZNAR, F., AND RAGA, J. 2001. Feeding ecology of the

loggerhead turtle Caretta caretta in the western Mediterra-

nean. Journal of Zoology 255:525–532.

WHITE, M. 2004. Observations of loggerhead turtles feeding on

discarded fish catch at Argostoli, Kefalonia. Marine Turtle

Newsletter 105:7–9.

Received : 26 October 2011

Revised and Accepted : 29 December 2011

Handling Editor : Jeffrey A. Seminoff


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