Blue whales passing around Azores

Abstract

Blue whale (Balaenoptera musculus) is an endangered species sighted every year
around the Azores. They pass by the archipelago during their spring migration, while travelling to their feeding grounds in the North Atlantic. We have analysed blue whale sighting data registered between 2006 and 2012 off the south coast of São Miguel (Azores) during commercial whale watching tours with Futurismo Azores Whale Watching. From 2009 onwards, records are more continuous and more complete than in previous years. In total we registered 76 encounters with blue whales, of which 30% were in 2010 and 40% in 2012. Our sightings were mostly between March and June, although one encounter was registered in July 2006 and another in September 2012. Individuals were photographically identified, resulting in 45 different whales over the 7 year study period. Eight whales were resighted in the area over a maximum period of five consecutive days, but there were no resightings over longer time. The number of blue whale sightings varied between years so it would be interesting to study this temporal distribution related to oceanographic features, like upwelling events, chlorophyll concentration or sea surface temperature. Looking forward, it would be also appealing to compare our blue whale catalogue to others of the Atlantic, and try to reveal more about their migrations and check for individual matches, since we did not find any between the studied years so far.

Full text

Laura González1,2, Clara Sardà1 & Miranda van der Linde1
1 Futurismo Azores Whale Watching, Ponta Delgada, São Miguel, Azores.
2 Department of Applied Physics, Vigo University, Vigo, Spain.
Corresponding author:
North Atlantic blue whales (Balaenoptera musculus)
are seen in tropical and warm temperate latitudes
during winter months, and further north in summer 1. In
the Azores they have been seen mainly during the spring
months 2.
The aim of this study is to determine the temporal
distribution of blue whales off São Miguel (Azores) and to
photographically-identify individuals registered between
2006 and 2012.
We have analysed blue whale sighting data registered
between 2006 and 2012 off the south coast of São Miguel
(Azores), during commercial whale watching (WW) tours
with Futurismo Azores Whale Watching. From 2009
onwards, records are more continuous and more
complete than in previous years. Animals were spotted
from land and from WW vessels by specialised observers.
Photos were also taken during this period, and those of
sufficient quality to distinguish natural marks and the
shape of the dorsal region, were used for identification
(Fig.1).
• 45 blue whales, have been identified, 20 from both sides.
- 8 whales were resighted, but only on consecutive days
(maximum interval of 5 days).
•77 sightings were registered on 62 different days
between 2006 and 2012, most of them in the last three
years (Table 1).
•Blue whales pass the Azores every year, mainly between
March and May (92.3%) (Table 1, Fig.2).
Bm18_right
Bm18_left
Bm7_right
Bm7_right
Fig.1. Examples of identified whales: shapes, colour patches, unique marks.
The next step along this line of research would be to analyse
patterns in temporal distribution in relation to Chlorophyll A
measures and sea surface temperature, and to link these factors
with upwelling events and phytoplankton blooms.
In the framework of this photo-ID project we propose a
comparison analysis with other catalogues in the Atlantic Ocean,
especially with the eastern population one, in order to learn more
about the blue whale migration.
Laura González
We would like to thank the Futurismo Azores
Whale Watching team, biologists and guides who have collected data for this
study, and especially, to thank the skippers and lookouts who have worked with
us everyday.
1) Reeves, R.R.; Smith, T.D.; Josephson, E.A.; Clapham, P.J. & Woolmer, G.
(2004). Historical observations of humpback whales and blue whales in the North Atlantic Ocean:
clues to migratory routes and possibly additional feeding grounds. Marine Mammal Science 20(4):
774-786. 2) Visser, F.; Hartman, K.L.; Pierce, G.J.; Valavanis, V.D. & Huisman, J. (2011). Timing of
migratory baleen whales at the Azores in relation to the North Atlantic spring bloom. Mar. Ecol.
Prog. Ser. 440:267-279.
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Table 1. Monthly and annual % of blue whale sightings.
Fig. 2. Temporal distribution of Balaenoptera musculus off São Miguel (2006-2012).