FOOD HABITS OF THE FRANCISCANA PONTOPORIA BLAINVILLEI (CETACEA: PLATANISTIDAE) FROM SOUTH AMERICA
JOHN E. FITCH California State Fisheries Laboratory, Long Beach, California 90802
AND ROBERT L. BROWNELL, JR. Los Angeles County Museum of Natural History, Los Angeles, California 90007
ABSTRACT The stomachs of 11 franciscanas, Pontoporia blainvillei (Gervais & D'Orbigny, 1844), captured offshore between Punta del Diablo and Playa la Coronilla, Uruguay, during February 1969, were examined for food. Of nine with fish remains, seven also contained other items: three, both squid and shrimp, and four, squid only. Two stomachs were empty. By utilizing the 132 fish otoliths from these nine stomachs, it was determined that at least 79 individuals were involved. Midshipmen, Porichthys porosissimus, and cutlassfish, Trichiurus lepturus, together accounted for 81 per cent of the piscine diet (72 and 9 per cent, respectively), while six other species (Macrodon ancylodon, Menticirrhus sp., Stromateus brasilien- sis, Urophycis sp., a pomadasyid, and an unknown) made up the remain- ing 19 per cent. The squids, identified from their beaks, were Lolliguncula brevis, but the shrimp could not be determined except to family Penaeidae. Based upon known habits and habitats of the prey species, the fran- ciscanas had been feeding at, or near, the bottom in the area of capture, and selectivity obviously plays an important role in their feeding behavior.
INTRODUCTION During February 1969, at the fishing village of Punta del Diablo, Uruguay, one of us (R.L.B.) removed and saved for laboratory examina- tion the stomach contents of 11 franciscanas (Pontoporia blainvillei [Gervais & D'Orbigny, 1844]) or La Plata dolphins. These dolphins had been caught by native fishermen in gill nets set at various depths above the bottom in approximately 20 m of water 20 to 30 km offshore, between Punta del Diablo and Playa la Coronilla, Uruguay. The nets are checked by the fishermen each morning, weather permitting, and franciscanas, sharks, and other enmeshed animals are taken out, the nets reset, and the catch brought ashore. On the beach, the blubber is cut from the dolphins, and the oil is rendered out for sale to the tanning industry. The dolphin carcasses, once the blubber is removed, are either thrown into the sea or left for foraging village pigs. Six previous reports on food habits of Pontoporia blainvillei span more 1971J Fitch & Brownell: Food Habits of the Franciscana 627 TABLE 1 FIELD DATA AND VITAL STATISTICS FOR 11 SPECIMENS OF Pontoporia blainvi/lei CAPTURED AT PUNTA DEL DIABLO, URUGUAY, FEBRUARY 1969
Field Length Weight Matu- Stomach number Date (em) (kg) rityt contents:!:
RLB 450 3 134 28.0 im. B, 0, S RLB 458 7 119 20.0 im. B, 0, S RLB 459 7 93 12.0 im. empty RLB 462 7 113 18.0 im. B, 0, S RLB 463 7 137 19.5 ad. B, 0 RLB 464 7 110 15.5 im. 0 RLB 465 7 137.5 29.5 ad. B, 0 RLB 466 7 138 28.0 ad. 0 RLB 467 7 128.5 24.5 im. B, 0 RLB 468 7 102.5 15.0 im. empty RLB 469 9 132.5 23.5 im. B, 0 t Maturity: im., immature: ad., adolescent. :f: Stomach contents: B, squid beaks; 0, otoliths: S, shrimp.
than a century, yet they contain little specific information. Four of the six accounts mention fish in the diet, but quantitative and qualitative data are vague or lacking. Burmeister (1867) reported finding "teeth (beaks) of a Cephalopodous animal, belonging to the family [sicJ Loligo, and also the lenses of the eyes of animals of the same group." Two years later he found in the first stomach of P. blainvillei, a fish 8 inches long, which he called "Peje-Rey {Atherina argentinensis Cuv. Valenc)," and some elytra of the beetle "Colymbetes" (Burmeister, 1869). "Curbinas" (Sciaenidae) and "lisas" (Mugilidae or Atherinidae) were noted by Lahille (1905), and in 1940, Cabrera & Yepes stated that franciscanas feed upon mullet, shrimp, and octopus. The two most recent reports list clupeids (almost 90 mm in length) and shrimps, Penaeus spp. (approximately 100 mm long) from the stomachs of two franciscanas captured off the coast of Santos, Brazil (Carvalho, 1961), and unidentified shrimp remains from specimens netted ofIUruguay (Van Erp, 1969).
METHODS AND MATERIALS The carcasses of 11 dolphins netted by fishermen were examined (Table 1), and the contents of each stomach were placed in a pan, where extraneous amorphic material was gently rinsed away. The remaining fragments, consisting primarily of fish otoliths, vertebrae and miscellaneous bones, cephalopod beaks, and shrimp were preserved in 50 per cent isopropyl alcohol. Formalin solutions cannot be used to preserve stomach contents where mollusk shells or fish otoliths are present, because the acids in 628 Bulletin of Marine Science [21 (2)
0\ \D .. V'l V'l 0\ .•.. '" N N l"'l N ,...., 0-'< " l"'l '
~<;) 'tl c... .~ ,--, r-.. -ci oj -....- flo. oj '--' " " r:l 0 5 0 " ~ 0. ~ :I: U " <: ~.~ ~I::,," r-.. r-.. '" ::E ~" -....-N N ~ 0 £:'" '-" .c" N I-< c" ' RESULTS Nine of the 11 dolphin stomachs contained recognizable remains from fish, squid, and shrimp. Two stomachs were empty. The squid beaks, present in seven stomachs, were from Lolliguncula brevis, one of several loliginid squids that occur in the area (Gilbert L. Voss, personal communi- cation). The shrimp were too digested to identify, except as members of the family Penaeidae; these were present in three of the 11 stomachs, but were not common in any. The 132 otoliths represented a minimum of 79 fishes belonging to eight species in six families (Table 2). Details regarding the fishes these otoliths represent are presented below in a family-by-family account. Batrachoididae Porichthys porosissimus (Valenciennes) Fig. I,F The 97 sagittae of midshipman are from a single species of Porichthys, and because of this they present an enigma. Gilbert (1968), in a review of the western Atlantic members of the genus, ascribed the range for P. porosissimus as Cape Henry, Virginia, to Necochea, Argentina, and designated as the lectotype (from among 10 syntypes in the Museum Na- tional d'Histoire Naturelle, Paris) a specimen from Rio de Janeiro, Brazil. The otolith he illustrated for P. porosissimus was from a fish collected in the Gulf of Mexico, and this otolith is distinctly (and specifically) different from the sagittae of Porichthys recovered from the dolphin stomachs. This can mean but one thing: namely, that the extensive latitudinal distribution ascribed by Gilbert for P. porosissimus is actually the overlapping range of two (at least) difficult-to-distinguish, yet distinct, species. The solution to this problem hinges upon determining whether the lectotype designated by Gilbert for P. porosissimus has (or did have, prior to preservation) otoliths similar to those found in the stomachs of Pontoporia, or whether they resemble those from Porichthys caught in the Gulf of Mexico. Gilbert (1968) did point out in his discussion of P. porosissimus that the species "apparently reaches a larger maximum size at the southern limits of its range" (p. 704), and that "individuals from southern Brazil and Uruguay, ... have somewhat higher [gill-raker] counts" (p. 705), but 630 Bulletin of Marine Science [21 (2) concluded that he had "no explanation for this." At the request of one of us (J.E.F.), Gilbert reexamined X-rays of his four largest individuals from Uruguay and southern Brazil, and these distinctly showed otoliths identical with the type that we found in the dolphin stomachs. If the lectotype of P. porosissimus contains this same type of otolith, the mid- shipman found in United States coastal waters south of Virginia will be- come Porichthys plectrodon Goode & Bean, 1882 (Carter R. Gilbert, personal communication). Two sizes of otoliths were present in the stomachs of Pontoporia. Seven- teen of the 97 ranged from 0.8 to 1.5 mm long and could have been trans- ferred to the dolphin stomachs from the digestive tracts of one of the other prey species, very likely Trichiurus or Lolliguncula. The other 80 otoliths were 4.2 to 10.0 mm long and represented midshipmen ranging to the maximum size (315 mm SL) reported by Gilbert. Midshipmen typically inhabit a muddy or sandy-muddy bottom, where they often lie partially or almost totally buried during daylight. They are most active at night, but even then they seldom swim any great distance up into the water column. Trichiuridae Trichiurus lepturus Linnaeus Fig. I,E Four of the stomachs of Pontoporia contained sagittae of the Atlantic cutlassfish. These 12 otoliths represented a minimum of seven individuals and were the second most abundant fish species eaten by these dolphins. Six of the 12 otoliths were relatively undigested, and these measured 4.2 to 5.3 mm long; the fish that the largest of these came from probably exceeded a meter in length. All of the dolphin stomachs that contained otoliths of Trichiurus also contained "swollen dorsal-fin elements" (Fierstine, 1968) which are abundant and readily observable in X-rays of many large, adult trichiurids. A fifth stomach (RLB 462, Table 2) con- tained five of these swollen bones, but no otoliths of Trichiurus. Tucker (1956) studied material from all parts of the world, and con- cluded that Trichiurus was represented by a single variable species, T. lepturus. He did not supply details as to behavior, but other authors report that Trichiurus "lives principally in the upper layers of the sea, being found from the surface to 191 fathoms (350 m)" (Wheeler, 1969); "is known to migrate into relatively shallow water to spawn" (Herald, 1961); is "caught in the open seas and bays, and estuaries" (Marshall, 1964); and occurs "in schools in shallow coastal and estuarine waters" (Munro, 1967). In the eastern north Pacific, Trichiurus is readily attracted to a bright light suspended above the surface at night. Otter trawls, and other bottom-fishing gear, almost invariably catch greater numbers of cutlassfish 1971] Fitch & Brownell: Food Habits of the Franciscana 631 FIGURE 1. Inner faces of teleost otoliths (sagittae) found in stomach of Pontoporia, captured off Uruguay during February 1969. Orientation (right or left) and length (mm) are noted for each figured otolith. A, Macrodon ancylodon, I., 14.0; B, pomadasyid, r., 1.7; C, Urophycis sp., I., 9.7; D, Stromatells brasiliensis, I., 7.1; E, Trichillrus lepturus, I., 4.3; F, Porichthys porosissimlls, I., 8.2; G, Menticirrhus sp., r., 3.5. Photos by Jack W. Schott. than do midwater or surface-fishing nets. T. lepturus probably exceeds five feet in length when fully grown. Sciaenidae Macrodon ancylodon (Bloch & Schneider) Fig. 1,A Two dolphins had fed upon this important food fish which occurs in small loose schools at or near the bottom in relatively shallow coastal waters 632 Bulletin of Marine Science [21 (2) (possibly to depths of 35 m). The pair of sagittae in the stomach of RLB 466 (Table 2) were in excellent condition and measured 14.0 mm long. These compare favorably in size to those from large adults, possibly 350 mm SL (Yamaguti, 1967). The remaining otolith of Macrodon was only 2.0 mm long, and very likely had been transferred to the dolphin stomach from a squid that had eaten the tiny fish it came from. Menticirrhus sp. Fig. I,G Six otoliths in three dolphin stomachs were from Menticirrhus. All were too digested to identify to species or to determine sizes of the fishes they came from. Members of this genus that have been studied are strictly bottom-dwelling species, preferring sandy to sandy-muddy habitat and relatively shallow depths. Travassos & Paiva (1957) listed two species of Menticirrhus for Brazilian waters; assuming no others are present, M. martinicensis is the more likely candidate of the two. Gadidae Urophycis sp. Fig. l,e Five otoliths of Urophycis were found in two of the dolphin stomachs (Table 2), and the pair of these that were relatively undigested measured 9.7 mm long. Although U. brasiliensis is the only member of the genus re- ported from the area, we have not seen otoliths from any South American Urophycis so we hesitate to identify our material to species or to comment on probable sizes. Urophycis is a bottom-dwelling fish, but on rare oc- casions, individuals or an entire school will forage for food a short distance above the bottom. Stromateidae Stromateus brasiliensis Fowler Fig. I,D One dolphin had eaten two of these fishes, one recently enough that the pair of otoliths, each 7.1 mm long, were in excellent condition. Haedrich ( 1967) reported that S. brasiliensis is the only member of the genus known along the Atlantic coast of South America, and gave its range as Tierra del Fuego north to Rio Grande do Sui, Brazil. Hart (1946) reported that, in the Patagonian region, individuals of Stromateus move shoreward to spawn in early summer, and at this time they aggregate in dense concentrations. During fall and winter, they move offshore into water as deep as 200 m and scatter. He also reported seasonal latitudinal movements for these fishes. Both individuals fed upon by RLB 463 (Table 2) had been adults; Hart 1971] Fitch & Brownell: Food Habits of the Franciscana 633 ( 1946) reported that adults of S. maculatus (= brasiliensis) range from 25 to 34 cm long and weigh 200 to 470 g. Pomadasyidae Unknown pomadasyid Fig. I,B One tiny otolith, 1.7 mm long, was too badly digested to identify beyond family. It probably had been transferred to the dolphin stomach from the digestive tract of either Trichiurus or Lolliguncula. Unidentified Fishes Four otoliths were too digested to identify with certainty. Two of these (in RLB 465, Table 2) were from a tiny fish, and are believed to have been transferred to the dolphin stomach from either Trichiurus or Lolli- guncula. DISCUSSION Fitch & Brownell (1968) bave shown the value of otoliths for determin- ing feeding habits of cetaceans, and Clarke ( 1962) pointed out that cephalopods can be identified by their beaks alone. Since fishes and cephalopods, heavily fed upon by cetaceans, are seldom found in a whale, dolphin, or porpoise stomach except as an otolith or a beak, it is necessary to retain and identify these structures if one wishes to conduct a meaningful food-habit study. By utilizing beaks and otoliths, we were able to identify seven kinds of fishes and a squid as having been fed upon by P. blainvillei, and to recognize that an additional fish species was involved in the diet. Based upon the known habits and habitats of these prey species, it can be speculated that these 11 dolphins had fed at or near the bottom, and that "selection" was involved in their feeding behavior. The greatest number of otoliths in the stomach of a single animal was 29 (RLB 464, Table 2). These represented a minimum of 15 midshipmen (determined by separating otoliths into rights and lefts, rather than dividing the total by two) and one Macrodon. The otolith of Macrodon may not have been from a primary prey of the dolphin, however. The greatest variety of otoliths in a single stomach occurred in specimen RLB 465 (Table 2). These were otoliths of the following: Porichthys, Trichiurus, Menticirrhus, Urophycis, and an unknown species. In this case also, at least one pair of otoliths had been transferred to the dolphin stomach from some other prey species. When any fish-eating predator becomes prey for some larger animal, the otoliths in its stomach are liberated in the larger animal by digestive action. 634 Bulletin of Marine Science [21 (2) Most squids feed voraciously on small fishes; as revealed in recent studies of Dosidicus by one of us (J.E.F.), over 200 otoliths turned up in the stomach of a 21-cm (mantle length) squid. Trichiurus is also noted for its voracious appetite and piscivorous feeding habits. Both of these are suspect in accounting for the tiny otoliths of Porichthys, Macrodon, the pomadasyid, and one of the unknowns. ACKNOWLEDGMENTS This investigation was supported in part by the National Science Founda- tion through a grant to Fitch (GB-6490) for his research on otoliths. Miss Rachel Ness helped with the field work, and Braulio R. Orrejas-Miranda, Museo Historia Natural, Montevideo, prepared the Spanish summary for us. Clifford H. Fiscus, Marine Mammal Biological Laboratory, Seattle, and Gilbert L. Voss, University of Miami, identified the squid beaks; Carter R. Gilbert, University of Florida, supplied additional information on western Atlantic species of Porichthys and their otoliths; and Mrs. P. Patricia Powell, Librarian, California State Fisheries Laboratory, put our literature citations in good order. Robert J. Lavenberg, Los Angeles County Museum of Natural History, and Dale W. Rice, U. S. Fish and Wildlife Service, Seattle, reviewed the manuscript. SUMARIO HABIT OS ALIMENTICIOS DE LA FRANCISCANA Pontoporia blainvillei (CETACEA: PLATANISTIDAE) DE AMERICA DEL SUR Los est6magos de once franciscanas, Pontoporia blainvillei (Gervais & D'Orbigny, 1844), capturadas frente a la costa entre Punta del Diablo y Playa la Coronilla, Uruguay, durante Febrero 1969, fueron examinados para estudiar su contenido. Dos est6magos estaban vaclos. De los nueve que tenian restos de peces, siete tambien tenian restos de otros alimentos: tres, tenian calamares y camarones, y cuatro, calamares s61amente. Me- diante los 132 otolitos de peces encontrados en estos nueve est6magos, se determin6 que estos provinieron por 10menos de 79 individuos. Porichthys porosissimus y Trichiurus lepturus representaron el 81 por ciento de la dieta de peces (72 y 9 por ciento, respectivamente) mientras otras seis especies (Macrodon ancylodon, Menticirrhus sp., Stromateus brasiliensis, Urophycis sp., un pomadasido y uno desconocido) representaron el restante 19 por dento. Los calamares, identificados por sus picos, eran todos Lolliguncula brevis, pero los camarones no pudieron ser identificados mas aHa de la familia, Penaeidae. Basandose en habitos conocidos yen los habitats de las presas, las fran- ciseanas habran estado alimentandose en el fondo 0 cerea de el en el area 1971] Fitch & Brownell: Food Habits of the Franciscana 635 de captura y la selectividad indudablemente juega un papel importante en sus Mbitos alimenticios. LITERATURE CITED BURMEISTER,H. 1867. Preliminary observations on the anatomy of Pontoporia blainvillii. Proc. Zool. Soc. Lond., 1867: 484-489. 1869. Pontoporia blainvillii Gray. In Descripci6n de cuatro especies de delfinides de la costa Argentina en el Oceano Athintico. Ana1. Mus. Publico Buenos Aires, 1: 389-445. CABRERA,A. ANDJ. YEPES 1940. Mamiferos Sud-Americanos. Vida, costumbres y descripci6n. Rist. Natural Ediar, Buenos Aires, 370 pp. CARVALHO,CORY T. DE 1961. "Stenodelphis blainvillei" na costa meridional do Brasil, com notas osteol6gicas (Cetacea, Platanistidae). Revta bras. Bio1., 21: 443-454. CLARKE, MALCOLMR. 1962. The identification of cephalopod "beaks" and the relationship be- tween beak size and total body weight. Bul1. Br. Mus. nat. Hist., Zool., 8(10): 419-480. FIERSTINE, HARRYL. 1968. Swollen dorsal fin elements in living and fossil Caranx (Teleostei: Carangidae) . Contr. Sci., No. 137: 1-10. FITCH, JOHN E. ANDR. L. BROWNELL,JR. 1968. Fish otoliths in cetacean stomachs and their importance in interpreting feeding habits. J. Fish. Res. Bd Can., 25(12): 2561-2574. GILBERT, CARTERR. 1968. Western Atlantic batrachoidid fishes of the genus Porichthys, in- cluding three new species. Bull. Mar. Sci., 18(3): 671-730. HAEDRICH,RICHARDL. 1967. The stromateoid fishes: Systematics and a classification. Bull. Mus. camp. Zoo!. Harv., 135(2): 31-139. HART, T. JOHN ] 946. Report on trawling surveys on the Patagonian Continental Shelf. 'Discovery' Rep., 23: 223-408. HERALD, EARL S. 1961. Living fishes of the world. Doubleday & Co., Inc., Garden City, N. Y., 304 pp. LAHILLE, F. 1905. Las ballenas de nuestros mares. Revta Jard. zoo!. B. Aires, 1(]]) : 28-82. MARSHALL,TOM C. 1964. Fishes of the Great Barrier Reef and coastal waters of Queensland. Angus and Robertson, Sydney, 566 pp. MUNRO, IAN S. R. 1967. The fishes of New Guinea. Department of Agriculture, Stock and Fisheries, Port Moresby, 651 pp. TRAVASSOS,H. AND M. P. PAIVA 1957. Lista dos Sciaenidae marinhos brasileiros, contendo chave de identifi- cac;ao e proposta de "nomes vulgares oficiais." Bolm Inst. Oceanogr., S. Paulo, 8(1 & 2): 139-169. 636 Bulletin of Marine Science [21(2) TUCKER, DENYS W. 1956. Studies on the trichiuroid fishes-3. A preliminary revision of the family Trichiuridae. Bull. Br. Mus. nat. Hist., Zoo1., 4(3): 73-130. VAN ERP, INGEBORG 1969. In quest of the La Plata dolphin. Pac. Disc., 22(2): 18-24. WHEELER, ALWYNE 1969. The fishes of the British Isles and north-west Europe. Michigan State University Press, East Lansing, Michigan, 613 pp. YAMAGUTI, N. 1967. Desova de pescada-foguete, Macrodon ancylodon. Bolm Inst. Oceanogr., S. Paulo, 16(1): 101-106.