Fraser's dolphin (<i>Lagenodelphis hosei</i> Fraser, 1956) in southern Brazil

Abstract

The Fraser's dolphin, Lagenodelphis hosei Fraser, 1956, is distributed in tropical oceanic waters worldwide. There is little information on the biology and distribution of this species in the Southwestern Atlantic Ocean. From September to November 1997, 10 stranded Fraser's dolphins were collected along the northern Rio Grande do Sul coast, southern Brazil. The reproductive status was determined for seven animals; the sample was comprised mainly of sexually mature dolphins. Total length varied from 241.0 to 245.0cm for females and 216.0 to 258.0cm for males. Several fetal bones were found in the vaginal channel of one female. Analyses of stomach contents from six animals revealed remains of coastal species of cephalopods, fishes and crustaceans, suggesting that these dolphins were feeding nearshore prior to stranding. Five dolphins had large quantity of the parasite Phyllobotrium delphini (larval stage) in the blubber layer, particularly in the genital region. Although this species is considered to be tropical in distribution, the records from the Southwestern Atlantic are concentrated in temperate areas (30-35°S). Fraser's dolphin strandings in Rio Grande do Sul were not isolated events, and several other were recorded for the Brazilian, Uruguayan and Argentinean coast in the same and subsequent years. This may represent a complex phenomenon involving several causes, such as transient oceanographic events, diseases and other variables.