Monitoring of the grey dolphin, Sota/ia fluviatilis ( Cetacea: Delphinidae ), off Fortaleza, Ceará State, Brazil.

Abstract

The grey dolphin, Sotalia fluviatilis, has its distribution in the Central and South Americas, from Honduras to Santa Catarinn, Brazil. In Fortaleza (03º43' S, 38º30' W), groups of the grey dolphin occur frequently throughout the year. This paper studies the distribution, abundanceand behavior ofthis cetacean, at Enseada do Mucuripe in Fortaleza, between January/92 and December/93. The distribution of sightings, and displacement routes ofSotalia fluviatilis at the Enseada, evidenced
the preferential use of the sites Praia Mansa and Praia de Iracema on diferent timings, suggesting movement patterns from resting and feeding areas respectively. l.Argest and smallest frequencies of sightings at Praia de Iracema occurred respectively at the first and fourth quarters. l.Argest frequencies happened at low tide .. The total number of individuais sought per day of observation varied between one and ten, and largest frequency of occurrence was of five individuais in the area. Annual variations in group size may be related with the high accidental mortality of dolphins in fishing nets, recorded during the study period. Aerial (total and partia I) and fishing (single, in group randomly, in group coopera tive) behaviors were observed on 38 occasions. Aerial behavior usually occurred in deeper areas after intense fishing activity in the group. The cooperative fishing was characterized by a sequence of movements apparently ordinnted, concentrating and trapping schools in deeper waters, bringing them to shore were feeding occurred. This behavior could be repeated several times a day.