Identification of Sotalia fluviatilis (Tucuxi)

Outside of Previously Reported Range

Talamanca Dolphin Foundation, Manzanillo, Talamanca, Costa Rica

Manzanillo, Talamanca, Costa Rica (SL, VS)

408 South Willson, Bozeman, MT 59715 USA

Abstract

Sotalia fluviatilis (tucuxi dolphins) were identified and observed on the southern Caribbean coast of Costa Rica, north of their previously reported range. From 5 April to 26 May, 1997, Sotalia fluviatilis, Tursiops truncatus (bottlenose) and Stenella frontalis (Atlantic spotted) dolphins were identified and observed from boats by sight and photographs. A photographic catalogue of distinct dorsal fins of some dolphins in the study area was begun. Behavior of groups of tucuxi-only, tucuxi-bottlenose and bottlenose-only was observed, raising some important questions about interspecific behavior of tucuxi-bottlenose groups. Consistency of location of tucuxi supports the concept of tucuxi having a limited home range for a given population. Underwater topography and the presence of muddy river runoff in the study area were documented as aspects of tucuxi habitat.

This study was designed to: 1) verify the presence of tucuxi (Sotalia fluviatilis) outside of its previously reported range, 2) add new information to the limited body of knowledge about this species, including interaction with other species of dolphins, 3) document habitat of the tucuxi in this area, and 4) document the presence of other dolphin species in the area.

The authors recently identified several different species of dolphins, one of which was tucuxi, in a coastal area on the Caribbean coast of Costa Rica, north of the previously reported northern range of this species (Panama). Local fishermen and skin divers have been encountering these dolphins in the near-shore waters and rivers of Costa Rica for generations. They recognized that some of the dolphins they saw were significantly smaller than others, and suspected they were a different kind of dolphin, referring to them as the "small ones", and also, "buffeo". In reviewing the literature, the authors found that no scientific study or identification of these dolphins on the Costa Rican coast had been previously reported.

To further substantiate the existence of the tucuxi in Costa Rican waters, an exploratory study was designed and conducted by the authors. The location chosen for this study was a coastal area where local fishermen and divers have consistently seen dolphins for decades. It is a partial bay, delineated by Punta Mona, a small key about 8 km north of the Panama border; and the Gandoca River, which is located approximately half way between Punta Mona and the border of Panama. The Gandoca River mouth is sometimes naturally closed off from the open ocean, and not the source of consistent muddy water found in the study area. This partial bay is characterized by a coral reef adjacent to the island, and a gently sloping series of sand shelves, which extend from the beach to 40 meters in depth off shore. At 3-4 km from shore, the slope changes to near vertical and vertical walls, dropping to a 104 fathom (197 m) tongue of deep water connecting the bay to the open sea. There is a shallow sand shoal in front of Mile Creek in the middle of the study area, and a small rock reef in front of Black Creek. Turbid water runoff enters the bay from the Sixaola River, which is the border of Costa Rica and Panama. This river is approximately 600-800 meters wide at its mouth. The "dirty water line", marking the juncture of the clear ocean water and the muddy Sixaola River water, is very visible within the study area, and shifts in relative location depending on rain, wind, current and sea state.(Fig. 1)

The tucuxi (Sotalia fluviatilis), a name given to this small dolphin by the Tupi Indians of the Amazon, is found in rivers, estuaries, lakes and nearshore marine waters of northeastern South America and eastern Central America (Ellis, 1982; Klinowska, 1991; Leatherwood and Reeves, 1983). The overall distribution of tucuxi has been reported to extend from Brazil to Panama. The freshwater form of tucuxi has been reported to inhabit the Amazon and Orinoco River drainages of South America. It is commonly seen in the Amazon, and has been found as far inland as southern Peru. The marine form of tucuxi has been previously reported to extend from the Florianopolis region, Brazil (27 degree 35’S, 48 degree 34’W), north to Panama (approximately 9 degree 22’N, 79 degree 54’W) (Borobia, 1991; Geise, 1991; Leatherwood, 1983). The abundance and status of these tucuxi populations are virtually unknown (Klinowska, 1991).

There are few experiences with captive tucuxi to contribute to general knowledge of this species. A small number of tucuxi were captured in the Amazon in the 1960’s and 1970’s for exhibition in the US and Europe. Some survived (Klinowska, 1991). The Cousteau Expedition to the Amazon in 1984 retained and observed a tuacuxi mother and calf in a temporary pool for two days in the Amazon (Cousteau, 1984). But the process of capturing live tucuxi in nets without harming them is made difficult by their relatively fast breathing rate (about every 30 seconds) making them vulnerable to drowning, and their susceptibility to shock (Herald, 1967). They are not considered as adaptable to captivity as other species, notably bottlenose (Martin, 1990). Tucuxi are also considered sacred animals in some areas where they are found, and local superstitions and beliefs further discourage capture or disturbance of these dolphins (Klinowska, 1991).

In order to effectively identify and study tucuxi in the wild, it is important to distinguish them from both the bottlenose

(Tursiops truncatus), also found in the same coastal and estuarine habitat; and the boto (Inia geoffrensis), sometimes sharing its riverine habitat.

The principal identifying features of the tucuxi are: 1) a relatively small body size (1.3-1.8 m)(Carwardine, 1995); 2) a stubby, robust body shape; 3) a tooth count of 26-35 pairs in each jaw; and, 4) a nearly triangular dorsal fin (Leatherwood, 1983; Ellis, 1982).

Color of the tucuxi differs according to habitat, but in general, the back is dark (ranging from blackish, through brown and dull lead gray, to pale bluish gray) and the belly light (ranging from white, to gray, to pink). The dorsal and ventral fields extend onto the face and flanks to various degrees. Tucuxi living in clearer coastal waters are generally darker than those living in the turbid Amazon. (Leatherwood, 1983)

The body of the tucuxi is similar to that of the bottlenose except that tucuxi have a slightly longer, more prominent beak, less clearly demarcated from the forehead than the bottlenose, and the body of the tucuxi as a whole, is stubbier (Leatherwood, 1983). Tucuxi are smaller than bottlenose, with a maximum length of 1.8 m, as compared to the maximum length of a bottlenose of 3.9 m (Carwardine, 1995). Young bottlenose dolphins are about the size of an adult tucuxi. Even though some tucuxi share similar coloration with some bottlenose (grayish above and lighter below), the dorsal fin of the tucuxi is lower in profile (only 110 to 127 mm high). Also, the shape of the dorsal fin is almost triangular, curving only slightly backward near the peak, as compared to the taller, broader-based, and more falcate dorsal fin of the bottlenose. (Leatherwood, 1983; Ellis, 1982).

Another dolphin sometimes sharing the tucuxi's riverine habitat, is Inia geoffrensis (the boto, or Amazon River dolphin) (Ellis, 1982). The boto, however, is distinguished from the tucuxi by its larger size (1.8-2.5 m)(Carwardine, 1995), its long narrow snout, and a low triangular ridge replacing the dorsal fin. The boto is also a slower and less active swimmer than the tucuxi (Leatherwood, 1983), and has a bluish-gray, vivid pink, or off-white body color.

Tucuxi emit an unusual double pulse structure of signals. These consist of both clicks of very high intensity, with a high repetition rate, and short duration, as well as a single whistle of pure tone and rising frequency (Norris, et al, 1972). Sonar click trains have been recorded in the Amazon and Orinoco Rivers from free ranging Sotalia and Inia (Kamminga, et al, 1993).

It is thought that a specific population of tucuxi remain within a limited home range (Leatherwood and Reeves, 1983). Any relationships between these various populations is unknown at this time (Klinowska, 1991).

The greatest threat to tucuxi at the present is probably modern fishing practices and the greatly increased intensity of fishing effort along the coasts and in the rivers within their range. Competition between man and dolphin for fish is still minimal in many areas, as the dolphins generally prey on sizes and classes of fish below those of commercial interest (da Silva, 1996). But, tucuxi are easily captured in monofilament gill nets, shrimp traps and seine nets, with drifting and fixed gill nets being the most lethal for tucuxi (da Silva, 1996). Other causes of tucuxi mortality are largely unknown.

Photoidentification of tucuxi and boto dolphins in the Colombian Amazon, using unique dorsal markings and natural pigmentation patterns, has been successful in identifying individual animals. (Gonzalez, 1994).

Material and methods of processing

Fifteen (15) observational excursions were made into the study area between April 5 and May 26, 1997. The study area was entered between 7:05 - 8:58 AM, based on recommendation from local fishermen and captains as the best time to see dolphins. Approximately two hours were spent in observation. (One trip was made in the afternoon between 16:00 and 17:30.) A total of four local boats (dugout canoes and open skiffs, most equipped with 25 hp engines), and eight different local boat captains were used. The research team consisted of primary observer, recorder, captain, and often one or more additional observers.

After entering the study area, the boat slowed its pace to search for dolphins. When the first group of one or more animals was spotted, the boat slowly approached the animals and then idled or cut the engine to minimize impact on the dolphins' behavior. As soon as dolphins were within observable range, a GPS position was recorded (Table 1). When possible, the approximate distance of the pod from the "dirty water line" was also noted.

Observations were recorded on standardized forms and included weather, sea conditions, any bird and fish activity, and dolphin behavior and activity. Dolphins within approximately 20 m. of the boat became a focal group and were visually followed and photographed whenever possible. Behavioral data were recorded in the following manner: visual observations and behavior were described primarily by the principal observer and photographer, supplemented at times by the recorder, captain, and any secondary observer(s). Once a group of one or more dolphins was spotted, it was assigned a number and date, and observed as unobtrusively as possible. Daylight observation continued until sufficient data was collected or until the dolphins left the area. Approximate size, coloration, and shape of dorsal fins were used to identify and differentiate species. Photographs were taken when possible, and correlated on the data sheet to pertinent information. The number of dolphins in the pod was estimated by number of visible animals at any one time, in addition to those at different surface locations within close proximity. Distinctive markings or shape of dorsal fins were recorded, photographed (when possible), and named for future recognition.

Behaviors were identified using previously accepted cetacean research terminology, as well as some further descriptions, as listed and described below. Previously used terminology included: milling, resting, fluke slap (tail slap), spy hops (head rise), nose outs, head outs, synchronized surfacing, leap, breach, pectoral fin slap, bow riding, surfing on wake of boat, fluke extension (tail wave), slow swim, traveling.(Kaufman and Forestell, 1986; Norris, 1994) Other behavioral descriptions used by the research team were: peduncle lift, snort, chasing, rough physical contact at surface, "wheezing" sound at inhale, surfing (on wake of boat), approaching, diving under boat, leaving area of boat, rolling over on side at surface, tail out, following and chasing fish, and backward breach. These behaviors were observed with such frequency that inclusion with the more accepted behavior descriptions seemed warranted.

Photographs were taken above water with two different 35 mm cameras, one equipped with a 300-mm lens, a second with a 38-115mm lens. A combination of color Ektachrome and Kodachrome print and slide film were used. Dorsal and body shots were used to substantiate species identification, behaviors, and to begin cataloging individual animals for repeat sightings, continued tracking and observation.

(A video recording was taken of tucuxi and other dolphins in the study area in June, 1997, to add further photographic information to this present study, but was not included in the data of this study.)

From April 5 to May 26, 1997, a total of fifteen (15) excursions were made into the study area, with dolphins sighted on fourteen (14) of those excursions. A total of (218) dolphins (tucuxi, bottlenose, and spotted) were sighted, with some obvious re-sightings made on different days. Dolphins having easily identifiable and unique dorsal fins, from shape or natural markings, were identified, named, and photographed, when possible. A catalogue of these individual dolphins was begun for tracking re-sightings and behavioral data. The closest and clearest dorsal ID shots were of bottlenose (Fig. 2) Several shots verified identification of the tucuxi species and confirmed tucuxi-bottlenose groupings, but were not close enough to identify an individual tucuxi dolphin (Fig. 3).

The number of sightings for each dolphin species, the boat and captain used, and the GPS position of the sighting may be seen in (Table 1). (Fig. 1) places the position of the sightings on a map of the study area. Tucuxi were identified from (N9:35.889) to (N9:37.688), north of its previously reported range of (N9:22’) in Panama. Tucuxi were identified by their more triangular shaped dorsal fin, smaller body size, and body coloration consisting of a dark gray back turning to pinkish-white on the belly. Tucuxi were seen and observed both in exclusive groups, as well as within groups of mixed tucuxi-bottlenose (Fig. 3). Bottlenose were also seen in exclusive groups. One group of spotted dolphins was sighted.

Group sizes for tucuxi-only ranged from (1-15), mixed tucuxi-bottlenose from (4-21), bottlenose-only from (2-8) and the group of spotted from (15-20). Six(6) groups of tucuxi-only, five(5) groups of bottlenose-only, eleven(11) groups of mixed tucuxi-bottlenose, and one(1) group of spotted dolphins were sighted (Table 1).

Some individual bottlenose with unique dorsal fins were identified, photographed, and given names. They will be entered in a catalog of individuals animals that will be used for continuing identification, re-sighting, and tracking purposes. Some of the unique and characterizing features of dorsal fins were: white marks of different sizes on the anterior portion of the fin, top part of fin apparently cut off, a folded over fin, and a variety of shapes of fins.

The "dirty water line", marking the boundary of river confluence with clear, open sea water, varied in relative location from day to day depending on rain, sea state, current, and wind. It was often noticed to be near dolphin sightings in which tucuxi were included.

Of the twenty-five(25) pods of dolphins encountered during the fifteen(15) excursions of the study, behavior of the dolphins varied considerably. These variations were both toward the research boat as well as within the group. As the boat spotted and approached a group of dolphins, there often seemed to be a difference in response, depending on the species of the dolphins. Groups of tucuxi-only seemed often to avoid close contact with the research boat, effectively keeping a distance of 200 ft or more, while maintaining their activity of resting, milling or following fish.

Groups consisting of tucuxi-bottlenose mixed, or bottlenose-only, showed more activity within the pod, and also more interest in the research boat. They often marked the boat's approach with tail slaps, followed by one or more animals approaching the boat with "head outs" and/or "spy hops", and then diving and passing under the boat, surfacing on the other side. Loud "snorts", up to 5 or 6 in succession, were sometimes heard from a single dolphin at the initial stage of the encounter. On numerous occasions, a low-keyed, unmistakable "whistle" or "wheeze" could consistently be heard on the inhale of one of the bottlenose.

Eleven(11) of the groups consisted of mixed tucuxi-bottlenose. On five or six occasions, when such a mixed group contained only one tucuxi with the rest bottlenose, vigorous splashing at the surface, and distinctly "rough" physical behavior was observed, lasting for 10-15 seconds. This activity seemed unique to this particular group or group configuration.

On five excursions, schools of herring were observed in the area, and on these days there were more birds in the area (pelicans, frigates, and scouas), sometimes diving for fish. The dolphins, on these days, also seemed to be following the herring and feeding, as evidenced by erratic, accelerated bursts of speed at the surface, rapid swimming, alternating between spreading out and bunching together, and lower interest in the research boat. These behaviors, interpreted as feeding behaviors, were further supported by several local fishermen/boat captains who said the dolphins like herring of the 20-24 cm size.

Other behavior of groups of mixed tucuxi-bottlenose, and bottlenose-only were: synchronized surfacing, pectoral slaps, breaching, leaping, salmon leaping, peduncle waving, rolling over on side at the surface, and backward leaps. Some days, the activity level observed was higher than others, and continued for longer periods of time. There was no obvious reason for this variation.

The consistent encounters with tucuxi and bottlenose dolphins in the study area during the months of April and May, 1997 confirm the local reports of a resident population of several species of dolphins in Costa Rican waters. The confirmation of the little-known tucuxi, north of its previously known range of Panama, is of considerable interest. Further investigation and research is needed to learn more about the year-around population, behavior patterns, range, and habitat of the tucuxi, and their interaction with other dolphin species.

A 12-month study would help determine movement patterns based on seasons. Examining water temperature, water composition and oceanographic climate changes could yield valuable additional data in better understanding tucuxi habitat.

The consistent, tightly grouped sightings of tucuxi within the study area seems to support the belief that tucuxi remain within a limited home range. Further investigation, identification and tracking of individuals and groups, may reveal aspects of habitat, population and social factors that influence the home range of this species. Continuing to add to a directory of individually recognizable dolphins of all species in this area would be helpful in tracking individuals and observing patterns of behavior.

The early morning hours during April and May did result in consistent sightings in the study area, and in a variety of behaviors to observe. Observation extended to all daylight hours would yield more information about daily behavior patterns.

The interspecific behavior of rough surface activity observed in the group(s) of bottlenose with one tucuxi warrants further observation and study.

Audio recordings of tucuxi sounds in this region could be added to those already recorded from tucuxi in the Amazon. Such recording data may eventually help determine the functions of these sounds, as well as identifying possible communication and dialects between populations.

The accessibility to the dolphins in this area is relatively easy, and is both an advantage for those wishing to see and study them, and a disadvantage when considering potential harm to the dolphins and their habitat. The study area is located in a remote area of Costa Rica, on the southern Caribbean coast. The closest village with reliable boat access is Manzanillo, whose small local economy is based on fishing, diving and eco-tourism. It has been isolated by poor roads and lack of telephone and electricity until the late 1980's.

The Gandoca-Manzanillo Wildlife Refuge includes the village of Manzanillo and surrounding terrestrial and off-shore region, and has been established to protect the rich bio-diversity of this tropical eco-system. Greater understanding and awareness of the marine life of the area, including dolphins, could contribute greatly to the goals of the Refuge, while at the same time taking advantage of the protection already intended for the wildlife of this region.

Acknowledgments

The authors owe much to the Talamanca Dolphin Foundation for the outcome of this initial project. We also thank Mary Ahlers for her contributions in data collection and observation, and the numerous native residents of Manzanillo who shared personal experiences and information about the dolphins of the area, and offered time and enthusiasm to the project. We also thank Dr.Paul Forestell, of Southampton College and the Pacific Whale Foundation, for his guidance in data collection. Jim DiBerardinis generously gave technical assistance and support throughout the study.

References

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Carwardine, M. (1995). In Whales, Dolphins and Porpoises, DK Publishing, Inc., New York,pp. 172-173.

Cousteau, J. & Richards, M.(1984). Sorrow In a Magic Land. In: Jacques Cousteau’s Amazon Journey. Harry N. Abrams, Inc., New York,pp.165-176.

Ellis, R.(1982). Dolphins and Porpoises. Alfred A. Knopf, New York, pp. 55-57.

Geise, L.(1991). Sotalia guianensis (Cetacea, Delphinidae) population in the Guanabara Bay, Rio de Janeiro, Brazil. Mammalia,Vol.55(3)pp.371-380.

Gonzalez, F.(1994). Use of Photoidentification to Study the Amazon River Dolphin Inia Geoffrensis in the Colombian Amazon, Marine Mammal Science,Vol.10(3),pp.348-353.

Herald, E. S.(1967). Boutu and Tookashee-Amazon dolphins. Pacific Discovery. Vol.20(1),pp.2-9.

Kamminga, C., Van-Hove, M. T., Engelsma, F. J., Terry, R. P.(1993). Investigations on Cetacean Sonar X: A comparative analysis of underwater echolocation clicks of Inia spp. and Sotalia spp. Aquatic Mammals. Vol. 19(1),pp.31-43.

Kaufman, G. & Forestell, P.(1984). Hawaii's Humpback Whales. PWF Press, Kihei, HI.

Klinowska, M.(1991). Dolphins, Porpoises and Whales of The World. The IUCN Red Data Book. IUCN, Gland,Switzerland and Cambridge,UK, pp.132-137.

Layne, J.N.(1958). Observations on Freshwater Dolphins in the Upper Amazon. Journal of Mammalogy. Vol.39,No.1,pp.1-22.

Leatherwood, S. & Reeves, R. R.(1983). Tucuxi. In: Sierra Club Handbook of Whales and Dolphins. Sierra Club Books, San Francisco,pp. 184-187.

Martin, A. R.(1990). Tucuxi. In: The Illustrated Encyclopedia of Whales and Dolphins. Portland House,New York,NY, p.135.

Mitchell, E.D.(Ed.)(1975). Review of the Biology and Fisheries for Smaller Cetaceans. Report of the meeting on smaller cetaceans, International Whaling Commission. Journal of Fishing Resources Board of Canada. Vol.32(7), pp.875-1240.

Norris, K.(1994) The Hawaiian Spinner Dolphin. University of California Press.

Norris, K.S., Harvey, G.W., Burzeel, L.A., & Krishna Kartha, T.D.(1972). Sound Production in the Freshwater Porpoises Sotalia cf. fluviatilis Gervais and Deville and Inia geoffrensis Blainville, in the Rio Negro, Brazil. Investigations on Cetacea. Bern, Institute of Brain Anatomy, University of Berne, Vol.4,pp.251-59.

da Silva, V.M.F & Best, R.C.(1996). Freshwater Dolphin/Fisheries Interaction in the Central Amazon (Brazil). Amazoniana. Vol.14(1-2),pp.165-175.

Walker, E.P.(1975). Mammals of the World, Third ed. Johns Hopkins University Press, Baltimore,London,pp. 1111-1112.

Captions of Figures and Table

Fig. 1. Study area: Costa Rica, Caribbean Coast.

Table 1. Summary of observational data and locations.

Fig. 2. a. two bottlenose dorsals

b. bottlenose dorsal

c. "Snow Cap" (bottlenose)

d. two bottlenose (behind)

Fig. 3. a. tucuxi(left), bottlenose(middle & right)

b. tucuxi(left), bottlenose(middle & right)

c. single tucuxi

d. tucuxi(left), unknown species(right)

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