FOOD OF A KILLER WHALE: EAGLE STING-RAY,MYLIOBATIS FOUND IN THE STOMACH OF
A STRANDED ORCINUS ORCA *HUGO P. CASTELLOModulo de Comunidades Nectonicas-Base Oceanografica Atlantica
Rio Grande, Brasil

ABSTRACTThe killer whale, Orcinus area feed on a variety of foods including sea mammals, sea birds, fishes and squids. Among fishes, teleosts seem to be more
frequently found in the stomach content than elasmobranchs. There are somerecords where electric ray, skates- and sharks are mentioned as preyed by killerwhales.
Eagle sting-ray, Myliabatis teeth plates were the only remain found in thestomach of a killer whale stranded on the beach of Rio Grande do Sul, Brazil.
As in the case of sharks that prey on sting-rays, six broken stings were foundembedded on the jaw and snout tegument. By comparison of the teeth plates,
the total length of the Myliobatis rays was estimated in a range of 65 to 81 ems.
INTRODUCTION

During the first week of November 1976 a killer whale, Orcinus area was stranded
3 km South of Lagoa dos Peixes bar and 120 km North of Rio Grande (R.S.,Brasil). During the last week of December two trips were made by the staff of theMuseu Oceanografico to the stranding place. During the first trip color slides
were obtained and the possibility of retrieving a part of the_ skeleton was considered. On the second trip, the complete head and the left flipper (M.0.R.G.
Cetacean coll. n° 37) were collected, some measurements were taken and the stomach content was preserved and identified.
The 5.60 m long male killer whale was almost dried and partially hurried insand above the high tide line. Through a left lateral cut the liver was reachedand under it the stomach was found. Numerous ray teeth, one cartilage, a broken shell and sand were retrieved.
STOMACH CONTENT

The teeth were identified as belonging to the eagle sting-ray, Myliobatis, a common venomous ray of the SW Atlantic waters and abundant during the summer
along Rio Grande do Sul coasts.

* Contribution of the Base Oceanografica Atlantica n° 1
Sci. Rep. Whales Res. Inst.,
No. 29, 1977, 107-111.

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CASTELLO

Teeth plates and venomous spines of the Whip rays, Dasyatis; Butterfly rays,Gymnura; Cow-nosed rays, Rhinoptera and Eagle rays, Myliobatis were dissected forcomparison with those obtained from the stomach content.
Two kind of Myliobatis teeth could easily be recognized, long rectangular ones
with slightly curved edges placed at the middle of the teeth plate and small polygonal ones on both sides of the middle series.
VENOMOUS STINGS
The killer whale was carefully inspected. The tegument had been loosing oil andwas partially dried. All injuries and scars were opened with scalpels and 6 piecesof broken venomous stings were easily seen and extracted from inside the tegument
at the following places:
sting A: 3.5 cm long at 10.5 cm distance, sligthly to the left of the tip ofsnout, upper jaw
sting B: 1.9 cm long at 4.0 cm distance below the 3rd upper right tooth,lower jaw
sting C: 4.3 cm long at 8.0 cm distance below the 8th lower tooth, lowerjaw
sting D: 1.0 cm long at 4.5 cm distance below the 4th lower tooth, lower jaw
sting E: 2.0 cm long at 9.0 cm distance below the 5th upper tooth, upper jaw
sting F: 2.0 cm long at 13.0 cm distamce from the tip of snout, lower jaw
KILLER WHALE FOOD HABITS
The killer whale of the West coast of North America feed on a variety of foods,including four main kinds: sea mammals (whales, dolphins, seals and sea otters);
sea birds; fishes (ling cod, Ophiodon; salmon, Oncorhynchus) and squids (Scheffer andSlipp, 1948).
The different preys of Orcinus orca had been carefully listed, including 10species of cetaceans, 8 pinnipeds, 11 teleosts, 6 other vertebrates and 3 varieties ofelasmobranchs (Martinez and Klinghammer, 1969).
It has been reported that a killer whale was observed to be feeding on an electric ray, Torpedo californica (Norris and Prescott, 1961) while unidentified skates andsharks are also mentioned among their diet (Tomilin, 1967).
The killer whales from the coastal waters of Japan feed mostly on fishes andcephalopods, but also feed on large numbers of cetaceans and pinnipeds (Nishiwakiand Handa, 1958).
The stomach content of 10 killer whales studied in the Eastern North Pacificcontained the remains of at least three California sea lions (Zalophus californianus;
four Steller sea lions (Eumetopias jubatus); seven Elephant seals (Mirounga angustirostris; two harbor porpoises (PhocOena phocoena); two Dall porpoises (Phocoenoidesdalli); one minke whale (Balaenoptera acutorostrata); two Opah fishes (Lampris regius);
one Pacific halibut (Hippoglossus stenolepus); two carcharinid sharks and one squidSci. Rep, Whales Res. Inst.,
No. 29, 1977.

FOOD OF A KILLER WHALE

109(Rice, 1968).
The leatherback sea turtle, Dermochelys coriacea, has been added to the known
prey of the killer whale from the St. Vincent Island (Lesser Antilles) (Caldwelland Caldwell, 1969).
DISCUSSION

Orcinus area has been recently included on the list of Rio Grande do Sul cetaceanson the base of eight stranding records (Castello and Gianuca, in press).
The stranding of November 1976 (8th. record) took place along one of thelongest sandy beaches of the SW Atlantic coast (from Chui to Torres), where sea
lions Otaria jlavescens and fur seals, Arctocephalus australis are seldom seen.
The La Plata dolphin or " Franciscana ", Pontoporia blainvillei has been considered as a possible prey of killer whales at Punta del Diablo (Dto. de Rocha,Uruguay) waters (Brownell, 1975), but until now this has not been documented.
It is also known that sharks frequently prey upon sting-rays. Dr Perry Gilbert (1977) from Mote Marine Laboratory, Florida, USA. recalled removing 96
sting ray spines from the mouth and lips of a 4.20 m long Hammerhead shark,Sphyrna mokarran. The spines were from the common sting ray, Dasyatis americana
and the little round sting ray, Urolophus jamaicensis. Also from the jaws and neckregion of a Hammerhead shark, Sphyrna z:ygaena (3.70 m long) caught in Beaufort
North Carolina, USA., 58 stings were dissected. In a second specimen, there wereremnants of 17 caudal spines in the stomach and at least 24 spines were in thegums. Stings can also be observed embedded in the tissues covering the jaw ofCarcharinus limbatus (13 stings) and of the Sharp-nosed shark, Scoliodon terra-novae(one sting) (Gudger, 1946).
A Black-tip shark, Carcharinus limbatus from North Carolina waters (3.0 mlong and 192 kg of weight) contained pieces of the Small Devil-fish, Mobula and inthree Tiger sharks, Galeocerdo tigrinus pieces of Mobula and Whip ray (Dasyatidae)
were found (Bell and Nichols, 1921). A Whip ray spine was imbedded in themuscle at the corner of the mouth of a 1.8. m long Carcharhinus commersonni collected
at the Bay of Forida (Nichols, 1917).
From the size and number of teeth plates recovered from the stomach content
and the size and number of the stings embedded on the jaw and snout of the killer
whale, six eagle sting rays, in a range of 65-81 cm of total lenght, were eaten.
Two species of eagle sting rays are mentioned for Rio Grande do Sul waters,Myliobatis freminvillei and M. goodei (Bigelow and Schroeder, 1953 ). Unfortunately
I am not able by the moment to distinguish both species on the basis of teeth orstings.
A broken shell of the bivalve, Pitar rostratus (Koch, 1844) also found in thestomach content was probably eaten by one of the eagle rays.
When caught in the killer whale's mouth each ray had in defense lashed out
with its long tail and at least 6 of them had left with the killer whale mementos of
their fights. Apparently no vital organ was injured by any of the stings.
Sci. Rep. Whales Res. Inst.,
No. 29, 1977.

CASTELLOllO

ACKNOWLEDGMENTS

To my friend, Prof. Norton M. Gianuca, Director of the Base Oceanografica Atlantica who identified the killer whale carcass and also to Miss Rosangela Lessa andMr. Lauro Barcellos and Mr. Rodney Nascimento who collaborated in taking measurements, color slides and helped to collect the head and flipper on the beach.
To Dr. Eliezer Rios, Director of the Museu Oceanografico who determined thebivalve shell and to Dr. Perry Gilbert; Dr. George Y. Harry, Director of theMarine Mammal Division, N.O.A.A., Seattle, Washington and Dr. James W.
Atz from The American Museum of Natural History, New York, USA. who kindly
helped me with bibliography and information.
REFERENCES
BELL, J.C., and J. T. NICHOLS, 1921. Notes on the food of Carolina Sharks. Copeia, 92: 17-20.
BIGELOW, H. B., and W. C. SCHROEDER, 1953. Sawfishes, Guitarfishes, Skates, Rays. Mem. Sears
Found. Mar. Res.. I, part 2: 1-514.
BROWNELL, R. L., 1975. Progress Report on the biology of the Franciscana dolphin, Pontoporia blainvillei,in Uruguayan waters. J. Fish. Res. Ed. Canada, 32 (7): 1073-1078.
CALDWELL, D. L., and M. C. CALDWELL, 1969. Addition of the Leather back sea turtle to the known preyof the killer whale, Orcinus orca. J. Mamm., 50 (3) : 636.
CASTELLO, H.P., and N. M. GIANUCA, (in press). Contribution to the study of the Cetacean fauna of Rio
Grande do Sul, Brasil. Atlantica, F.U.R.G. (Rio Grande).
GILBERT, P., 1977. Personal communication.
GUDGER, E.W., 1946. Does the sting ray strike and poison fish(!s? Sci. Montly 63 (2): 110-116.
MARTINEZ, D. R., and E. KLINGHAMMER, 1969. The behavior of the whale, Orcinus orca ; a review of theliterature.
Tierpsychol., 27: 828-839.
NORRIS, K. S., and J. H. PRESCOTT, 1961. Observations on Pacific cetaceans of Californian and Mexican ,waters. Univ. Calif. Publ. Zool., 63: 291-402.
NICHOLS, J. T., 1917. Ichthyological notes from a cruise off Southwest Florida, with description of Gobiesox
yuma, sp. nov. Bull. Amer. Mus. Nat. Hist., 37: 873-877.
NrsHIWAKI, M., and C. HANDA, 1958. Killer whales caught in the coastal waters of.Japan for recent tenyears. Sci. Rep. Whales Res. Inst., 13: 85-96.
RrcE, D. W., 1968. Stomach contents and feeding behavior of killer whales in the Eastern North Pacific.
Norsk Hvalfangst-Tid., 2 : 35-38.
SCHEFFER, V. B., and J. W. SLIPP, 1948. The whales and dolphins of Washington State with a key to thecetaceans of the west coast of North America. The Amer. Mir/land Nat., 39 (2): 257-337.
ToMILIN, A. G., 1967. Mammals of the U.S.S.R. and alijacent countries. vol IX. Cetacea. Israel Program for
Scientific Translations, Jerusalem, 717 p.

z.

Sci. Rep. Whales Res. Inst.,
No. 29, 1977.

FOOD OF A KILLER WHALE

EXPLANATION OF PLATE
PLATE I
Fig. I. Left middle series teeth of the upper plate (n° 1) of an eagle sting-ray,
Myliobatis estimated to be 81.5 cm long, eaten by the killer whale. Right-Lower
plate of the same specimen.
Fig. 2. Eagle ray teeth in different positions, three first rows are middle teeth,
fourth row are lateral ones.
PLATE II
Fig. I. Dorsal aspect of the lower teeth plate (n° 3) of an eagle sting-ray eaten by
the killer whale.
Fig. 2. Ventral aspect,
PLATE III
Fig. I. Labial cartilage of an eagle-sting ray found in the stomach content.
Fig. 2. Rests of a Pitar rostratus bivalve shell, probably eaten by one of the stingrays.
PLATE IV
Six pieces of eagle ray stings that were embedded on the jaw and snout of the killer
whale.

Sci. Rep, Whales Res. Inst.,
No. 29, 1977.

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