15ª Reunión de Trabajo de Expertos en Mamíferos

Acuáticos de América del Sur

9º Congreso SOLAMAC

Puerto Madryn, 16 al 20 de septiembre de 2012

STENO BREDANENSIS IN RIO DE JANEIRO, SOUTHEASTERN BRAZIL: INSIGHTS ON ECOLOGICAL PARAMETERS

R.R. Carvalho

1,2,3 ; L. Bittencourt

1; L. Flach

4; J. Laílson-Brito

1 & A.F. Azevedo

1

1 Laboratório de Mamíferos Aquáticos e Bioindicadores “Profª Izabel Gurgel” – Universidade do

Estado do Rio de Janeiro (UERJ) ² Programa de Pós Graduação em Oceanografia/UERJ

³ Bolsista CAPES 4 Instituto Boto-Cinza, Rua Santa Terezinha, Vila Muriqui.

Information on rough-toothed dolphin (Steno bredanensis) is scarce for the coast of

Brazil and little is known about its ecology and population parameters. Between 2008

and 2012 surveys were conducted in coastal waters of Rio de Janeiro city (RJ) aiming at

providing information on ecological parameters of S. bredanensis along the coast.

These surveys were conducted following a predefined zigzag transect. All transect lines

were two kilometers distant from each other and had a perpendicular distance from the

coast of eight kilometers. When a group of dolphins was sighted, information of group

size, behavior and depth were collected every five minutes. The photo-identification

technique was conducted aiming at identifying the group members. Frequencies of

occurrence (FO) were calculated for each dolphin identified by the formula FO = (ni x

100)/Na, where (ni) is the total number of days an individual was identified and (Na) is

the total number of survey days. It was possible to compare the identified animals in RJ

with a catalog of Steno bredanensis photographed in Ilha Grande Bay (IGB), located

140km south of Rio de Janeiro city. A total of 26 surveys were conducted in RJ and

sightings were possible in nine (34.6%) days. Groups (N=13) were encountered in

depths from 9 to 50.9 meters (22.2 ± 8) and varied in size from 2 to 48 individuals (33.3

± 15). The sightings of rough-toothed dolphins in RJ were predominant (N=6; 66.6%)

between June and July. However, sightings also occurred on April, May and November

with groups (N = 3) varying from 15 to 48 (33.3 ± 20.6) in size. Feeding (53.9%) was the

most common behavior, followed by traveling (36.7%), milling (6.3%), resting (2.3%) and

socializing (0.8%). It was possible to verify that during feeding behavior Cutlassfish

(Trichiurus lepturus) was one of the prey items of S. bredanensis in RJ. However, it was

not possible to estimate its importance in relation to other possible preys. A total of 127

animals could be catalogued in RJ. Of these, 63 were re-sighted in this area.

Frequencies of occurrence varied between 11.1% and 100% (31.5 ± 22). Seven

matches were possible among animals identified in IGB and RJ. The annual re-sightings

and higher values of feeding behavior are an indication of seasonal site fidelity with

feeding purpose. Moreover, animals re-sighted in both bays showed that some

individuals are able to use other coastal areas along Rio de Janeiro State.