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First record of Omura's whale, Balaenoptera omurai, in Sri Lankan waters

Article · June 2017with40 Reads
DOI: 10.1186/s41200-017-0121-2
Abstract
An unusually coloured, small baleen whale was documented off the southern coast of Sri Lanka in February 2017 during routine field surveys. Based on five distinct morphological characteristics including jaw asymmetry, presence of a prominent central rostral ridge, blaze on right side, asymmetrical chevron on left and right sides and a strongly falcate dorsal fin the individual was positively identified as an Omura’s whale (Balaenoptera omurai). This discovery represents the first confirmed sighting of Omura’s whale in Sri Lankan and therefore central Northern Indian Ocean waters.
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M A R I N E R E C O R D Open Access
First record of Omuras whale, Balaenoptera
omurai, in Sri Lankan waters
Asha de Vos
Abstract
An unusually coloured, small baleen whale was documented off the southern coast of Sri Lanka in February 2017
during routine field surveys. Based on five distinct morphological characteristics including jaw asymmetry, presence
of a prominent central rostral ridge, blaze on right side, asymmetrical chevron on left and right sides and a strongly
falcate dorsal fin the individual was positively identified as an Omuras whale (Balaenoptera omurai). This discovery
represents the first confirmed sighting of Omuras whale in Sri Lankan and therefore central Northern Indian Ocean
waters.
Keywords: Northern Indian Ocean, Sri Lanka, Omuras whale, Sri Lanka, Distribution, Balaenoptera omurai
Background
Originally misclassified as a pygmy form of Brydeswhale
(Balaenoptera edeni) in the 1970s, the Omuras whale has
since been described as a distinct baleen whale species of
the family Balaenopteridae (Wada et al. 2003). Sasaki et al.
(2006) showed that in fact the Omuras whale represents
an ancient independent lineage that diverged around 17
million years ago within the Balaenopteridae.
This species is currently confirmed from the north-
eastern and South Atlantic, western Pacific and Indian
Ocean. The records from the Indian Ocean are largely
from the eastern Indian Ocean and more recently, with
the discovery of a resident population of Omuras whales
in Madagascar, the southwestern Indian Ocean and one
from Iran in the northwest Indian Ocean.
This discovery represents the first confirmed docu-
mentation of Omuras whale within Sri Lankan waters
and therefore the first from the central Northern
Indian Ocean.
Results
An Omuras whale was photographed on 5 February
2017 during routine blue whale photo-identification sur-
veys. The solitary individual was documented approxi-
mately 7 km from shore in water between 5565 m deep
(Fig. 1). As the research vessel was switched off, the
animal approached the boat enabling a series of photo-
graphs highlighting a number of key morphological
characteristics to be taken. These characteristics include,
jaw asymmetry (Fig. 2a and b), prominent single central
rostral ridge and not three as found in B. edeni (Fig. 2b),
blaze on right side (Fig. 2c), asymmetrical chevron on
both right and left sides (Fig. 2c and d) and falcate dorsal
fin (Fig. 2e). These characteristics allow us to morpho-
logically distinguish this individual from Brydes whales
that are commonly recorded in Sri Lankan waters.
The following morphologically diagnostic features
enabled the identification of this individual as an
Omuras whale (Fig. 2).
1. Jaw asymmetry
As described by Cerchio et al. (2015), this individual
showed evidence of asymmetrical colouration of the
lower jaws, with a darkly pigmented left jaw (Fig. 2a)
and lightly pigmented right jaw (Fig. 2b).
2. Presence of a prominent single medial ridge
The prominent rostral ridge and absence of
pronounced lateral ridges (only lightly visible)
enabled differentiation from the more commonly
sighted Brydes whale with central ridge and lateral
ridges (Wada et al. 2003).
3. Presence of right side blaze
As described by Cerchio et al. (2015)white
pigmentation is more extensive on the right side
of the body compared to the left. This individual
Correspondence: ashadevos@gmail.com
Oceanswell and The Sri Lankan Blue Whale Project, 131 W.A.D. Ramanayake
Mawatha, Colombo 2, Sri Lanka
© The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0
International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and
reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to
the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver
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de Vos Marine Biodiversity Records (2017) 10:18
DOI 10.1186/s41200-017-0121-2
also showed evidence of a lightly pigmented blaze
anterior to the eye only present on the right side
and multiple dark stripes bisecting the blaze.
4. Asymmetrical chevron on both right and left sides
Lightly pigmented chevron anterior to the dorsal fin
evident on both sides but more pronounced on right
side of the body, displaying a double-banded pattern
also described by Cerchio et al. (2015).
5. Strongly falcate dorsal fin
The dorsal fin was pointed, strongly falcate and
backswept (Wada et al. 2003; Cerchio et al. 2015;
Jefferson et al. 2008; Ranjbar et al. 2016)
Apart from the distinguishing characteristics, this indi-
vidual also possessed a mark that resembled a tyre mark
on its left dorsal flank and an entanglement scar on the
tip of its left rostrum. Both these markings appear to be
made by external interactions and are not characteristics
of this species.
Discussion
The morphological characteristics described through the
photographs taken on 5 February 2017 provide evidence
for the presence of Omuras whales in Sri Lankan waters
and thereby the central Northern Indian Ocean. A previ-
ous record from Iran already indicated presence of this
species within the western Northern Indian Ocean
(Ranjbar et al. 2016). This is the only confirmed record
of an Omuras whale in Sri Lankan waters to date. This
is a new record within an expected range within which
few sightings/records have previously been available.
The detailed description of the external features of this
species provided by Cerchio et al. (2015) were useful for
the identification of this individual within Sri Lankan
waters. The key features of interest that enable us to
discern between Omuras and Brydes that are often
recorded in these waters include the prominent dorsal
ridge on the rostrum (Brydes whales often have three
head ridges; the central ridge is flanked by two lateral
Fig 1 Map showing sighting location of Omuras whale off southern Sri Lanka encountered on 5 February 2017. Black dot on southern coast
represents the location of the sighting, which was approximately 6.9 km offshore in water that was between 5565 m deep
de Vos Marine Biodiversity Records (2017) 10:18 Page 2 of 4
rostral ridges), body colouration (Brydes whales are dark
throughout their bodies), and the shape of the dorsal fin
(which is small and falcate in relation to that of the
Brydes whale) (Yamada 2009).
The tyrelike markings observed on the left dorsal
flank of this individual may represent attachment sites of
a remora (Echeneidae) as speculated by Cerchio et al.
(2015). Remoras are commonly seen attached on blue
whales in Sri Lankan waters, but do not leave any visible
markings of this nature likely due to a difference in the
physical characteristic of the dermis (Cerchio, pers.
Comm..).
This individual also showed evidence of an entangle-
ment scar on the left side of its upper jaw indicating that
this is a potential threat for this species in these waters.
Because the range of this species is still unknown the
threats they face are yet unclear making the documenta-
tion of this entanglement scar particularly important.
Bycatch in local fisheries has been reported from
Songkhla, Thailand (Adulyanukosol et al. 2012), and
given its penchant for shallow water habitats, bycatch is
likely a threat throughout its range (Cerchio et al. 2015).
In Sri Lankan waters, ship-strike is the leading
population-level threat to blue whales, followed by
Fig 2 Omuras whale documented off southern Sri Lanka on 5 February 2017. The morphological characteristics captured in these images distinguish
this individual from Brdyes whales that are commonly seen in Sri Lankan waters. These characteristics include; Jaw asymmetry with aleft jaw being
dark in colour compared to the bright jaw which is light in colouration; cprominent single ridge on rostrum and weak lateral ridges on each side;
Chevron on dright (more prominent) and eleft sides;andfstrongly falcate dorsal fin. Other markings of note include aentanglement
scar on left upper jaw and gtyre markon left dorsal flank
de Vos Marine Biodiversity Records (2017) 10:18 Page 3 of 4
incidental catch which includes both entanglement and
bycatch (de Vos et al. 2016). Given the smaller size of
Omuras whales compared to blue whales it can be con-
sidered a particularly pertinent threat to this species in
Sri Lankan waters.
The population of Omuraswhalesoffnorthwest
Madagascar was preferentially seen in water that was
4202 m deep with SST between 27.4 and 30.2 °C
(Cerchio et al. 2015). The sighting reported here was
made in waters 5565 m deep within 7 km of the
coast providing further evidence that these whales
prefer shallow shelf waters.
Cerchio et al. (2015) suggested that because extensive
genetic sampling of Brydes whale populations in the
North Indian Ocean did not reveal evidence of B. omurai
(Kershaw et al. 2013), the distribution of this species is
discontinuous with the Madagascar population being po-
tentially isolated from the eastern populations. However,
this record from Sri Lankan waters and a previous record
from Iran (Ranjbar et al. 2016) may provide some evi-
dence of connectivity across their range.
Given the rarity of this sighting it is important to con-
tinue to monitor and record sightings of this species,
document resightings of individuals across years and
within seasons to estimate population abundance and
define movements and ranges, clarify the distinction
between Omuras and Brydes whales to ensure accurate
records and identify the threats faced by this species.
The images illustrate the characteristic features of this
species and highlight the importance of field surveys and
photo-identification work that enable the discovery and
description of new species and provide opportunity to
expand our knowledge of the marine mammals inhabit-
ing our oceans. As such, please submit any images of
Brydes whales or Omuras whales from Sri Lankan
waters, to the respective catalogues by contacting the
corresponding author.
Conclusions
This is the only confirmed record of Omuras whales
from Sri Lankan waters and the central Northern Indian
Ocean. It is a new record within an expected range
within which few sightings/records have previously been
available and may provide some evidence of connectivity
with the populations in the eastern Indian Ocean.
Acknowledgements
All research reported in this manuscript was conducted under a Department
of Wildlife Conservation, Sri Lanka permit (number WL/3/2/1/18). I would like
to acknowledge Robert Brownell Jr. and Salvatore Cerchio for help in confirming
the sighting. Further, I wish to thank my field team Ariesha Wikramanayake, Ben
Yexley and Rosalind Bown for their assistance through the field period. Finally, I
wish to thank Andrew Lewin for help in producing the map indicating the
location of sighting.
Funding
Fieldwork was conducted using funds from a National Geographic Emerging
Explorer grant.
Availability of data and materials
The datasets used and/or analysed during the current study are available
from the corresponding author on reasonable request.
Authorscontributions
AdV conducted the fieldwork, analysed the photos and wrote the paper.
Competing interests
The author declares that she has no competing interests.
Consent for publication
Not applicable.
Ethics approval and consent to participate
Not applicable.
PublishersNote
Springer Nature remains neutral with regard to jurisdictional claims in
published maps and institutional affiliations.
Received: 27 April 2017 Accepted: 5 June 2017
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de Vos Marine Biodiversity Records (2017) 10:18 Page 4 of 4
  • [Show abstract] [Hide abstract] ABSTRACT: A juvenile rorqual live-stranded on Qeshm Island, Iran, in the northern Strait of Hormuz, Persian Gulf, in September 2007. The cause of stranding remains unknown but the whale (QE22.09.2007) showed no severe traumatic injuries nor was it emaciated. Six key morphological features, diagnostic in combination, allow positive identification as Omura's whale Balaenoptera omurai, a species that has not before been reported from the NW Indian Ocean. Features include diminutive body size (397 cm); an unusually large number of ventral grooves (n=82) and grooves near the midline extended caudad of the umbilicus; a strongly falcate, pointed dorsal fin; asymmetric colouration of the head (especially lower jaws) reminiscent of fin whale, and unilateral dark (eye, ear, flipper-to-flank) stripes; faint/incomplete lateral rostral ridges; and extremely low number of short, broad baleen plates (204 in right jaw). The likelihood for the existence of a local B. omurai population in the eastern Persian Gulf or Arabian Sea is deemed higher than the wandering of a small juvenile or mother/calf pair from any of the known distant distribution areas in the eastern or south-western Indian Ocean. This is the first record of Omura's whale for the Persian Gulf and Iran. Combined with two recent strandings of similar juveniles in the Atlantic (Mauritania, Brazil) it suggests that B. omurai may have a significantly wider (sub) tropical distribution than hitherto assumed.
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