Rare or cryptic? The first report of an Omura's whale (Balaenoptera omurai) in the South Atlantic Ocean

Abstract

The Omura's whale (Balaenoptera omurai), previously referred to as a small form of Bryde's whale, was described in 2003 as a distinct baleen whale species of the family Balaenopteridae. Omura's whales are currently confirmed to occur in three of the world's oceans; the western Pacific, Indian, and northeastern Atlantic. Here we report the genetic identification and a morphological description of a 4.16 m female calf of an Omura's whale found stranded in Pecém beach (03°32′11.6″S, 38°47′51.8″W), northeastern Brazil, in 2010. The three mitochondrial DNA markers (control region, cytochrome b, and cytochrome c oxidase subunit 1) unequivocally identified the specimen as a B. omurai, providing the first report of this species in the South Atlantic Ocean. The morphological identification of the specimen was limited due to the absence of the skull and loss of color pattern, but the proportions of the body were not consistent with the other balenopterid species and a single rostrum ridge distinguished it from Bryde's whales. This, together with the record of another juvenile in Mauritania, suggests the existence of an autochthonous Atlantic population of Omura's whales and indicates a necessity of reassessment of specimens indicated as Bryde's whale in the region.

Global Distribution of Omura’s Whales (Balaenoptera omurai) and Assessment of Range-Wide Threats

“…Documented mortalities include ship strikes, fisheries bycatch, and local traditional hunting, and there exist clear threats from coastal development and industry. Given the potential for the species to be characterized by small localized populations, and the currently documented low genetic diversity throughout its range (Wada et al, 2003;Cerchio et al, 2015;Cypriano-Souza et al, 2016), it may be particularly vulnerable to impacts from existing anthropogenic threats. Our review of accounts provides a first global assessment of range that could be useful in assessing risks, by modeling habitat suitability on a global scale and mapping the overlap of Omura's whale habitat with anthropogenic threats such as shipping traffic, fisheries and industrial activities.…”

“…Western South Atlantic Ocean (see Figure 6 for Detail) Brazil A single stranded whale was genetically identified as an Omura's whale from Pecém beach, São Gonçalo do Amarante, Ceara State in northeastern Brazil. The specimen was incomplete (missing most of the skull) but estimated "within a few centimeters" to be a 4.16 m female (Cypriano-Souza et al, 2016), and therefore a calf still dependent on its mother. Together with the Mauritania account, also of a dependent calf, the authors argue that these strandings more likely represented a regional population or populations as opposed to vagrants from another ocean basin, furthering the evidence for extension of the species range into the Atlantic Ocean.…”

“…Moreover, the exclusively tropical and warm-temperate distribution results in many documented populations occurring off the coasts of developing countries, for which there is typically little regulation of such threats and anthropogenic activities. If results from initial population studies in Madagascar bear out to apply range-wide, and the species is characterized by small, localized populations, with low range-wide genetic diversity (Wada et al, 2003;Cerchio et al, 2015;Cypriano-Souza et al, 2016), then they may be particularly vulnerable to such anthropogenic impacts that could cause small populations to decline. The distribution of the species in typically remote and poorly surveyed regions exacerbates the problem, in that both occurrence of interactions and magnitude of impacts is difficult to impossible to document.…”

Cetacean movements in coastal waters of the southwestern Atlantic ocean

“…As of October 2018, 47 cetacean species were reported in Brazilian aquatic environments (Santos et al 2010a, Cypriano-Souza et al 2017, which represents ca. 50% of all described species worldwide (see Committee on Taxonomy 2017).…”

Occurrence of Omura’s whale, Balaenoptera omurai (Cetacea: Balaenopteridae), in the Equatorial Atlantic Ocean based on Passive Acoustic Monitoring

“…The current distribution of Omura's whale includes the tropical and warm temperate Indo-Pacific, Indian, and North and South Atlantic Oceans (Wada et al 2003;Cerchio et al 2015;Jung et al 2016;Cypriano-Souza et al 2017;Ottewell et al 2016;Ranjbar et al 2016;Yamada 2018, Cerchio et al 2019). In the Atlantic Ocean, the only evidence of the presence of B. omurai is based on two beach cast specimens: 1) a specimen stranded in September 2010 on the beach of Pecém, Ceará, Northeast Brazil (3.53378° S, 38.79772° W) in the western South Atlantic (Cypriano-Souza et al 2017); and 2) a specimen stranded in November 3 2013 near Chott Boul on the coast of Mauritania (16.54146° N, 16.45055° W) in the eastern North Atlantic (Jung et al 2016).…”