A review of Balaenoptera strandings along the east coast of South America

Abstract

The genus Balaenoptera comprises seven species and 15 subspecies whose conservation statuses range from “Endangered” to “Least Concern” and “Data Deficient”. In addition to data from whaling and offshore cruises, much of the information related to these whales in the Southwestern Atlantic Ocean (SWAO) comes from beached carcass analysis. We reviewed published and unpublished confirmed records of Balaenoptera strandings along the east coast of South America (from ∼12∘N to 55∘S) to evaluate spatio-temporal ecological and habitat use patterns. A total of 223 strandings from the seven species were documented from 1865 to 2018: B edeni, more recently referred to as B. brydei in the SWAO (n=83), B. acutorostrata (n=64), B. bonaerensis (n=23), B. borealis (n=19), B. physalus (n=25), B. musculus (n=8), and B. omurai (n=1). As expected, most of the species occurred in higher numbers during the winter and spring migration seasons to/from low latitudes. Balaenoptera brydei and some individuals of B. acutorostrata were found year-round along the Brazilian coast. Although we may be underestimating the total number of strandings because unidentified whales were not included, and some records were probably not recorded considering the vast area as well as effort differences among regions, this is the most complete data set for strandings in Eastern South America. This supported different theories, such as possible sexual segregation for B. borealis (especially of pregnant females), a calving area for the same species in mid-latitude waters of the SWAO, and a larger B. acutorostrata calving area than previously expected (from ∼17∘S to 35∘S). The apparent increase in efforts towards beach surveys in Eastern South America, such as a network for marine mammal stranding information in Brazil (REMAB), will be of great value to fill knowledge gaps related to Balaenopteridae species in the area.