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Understanding Blue Whales off Azores.

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Abstract

Every year great baleen whales appear around Azores archipelago. We have analyzed data registered from whale watching platforms off São Miguel since 2008 to 2014. We recorded 7597 sightings of 21 different species, and of those, 643 were baleen whales. Blue whale (Balaenoptera musculus) has been the third most sighted baleen whale (95 sightings), after fin whale (Balaenoptera physalus) (330) and sei whale (Balaenoptera borealis) (159). All blue whale sightings but one were made between March and June, been more than 75% in April-May. To identify habitat preferences we applied Generalized Additive Models (GAMs) and analyzed these presence/absence data according with several physiographic (depth, slope, distance to the coast and position), and remote-sensing variables (sea surface temperature, chlorophyll a, sea surface height). We could explain more than 40% of the blue whales distribution using all these variables. During this time we have photo-identified 88 different individuals, resighting in 2014 three whales already seen in earlier years. These findings suggest the possibility of two of them travelling together during the last two years. For a better understanding of blue whales migration, we suggest to take into account in the models other variables as distance to the oceanographic fronts, as well as try different temporal resolution variables. In another hand, comparing our photo-id catalogue with others in the Atlantic will be essential to confirm possible migration routes.
Laura González1,2, Miranda van der Linde1 & Jesús M. Torres Palenzuela2
Laura González
Blue whales (Balaenoptera musculus) occurrence in N and NW
North Atlantic has been already studied [1,2]. However, even
they are seen regularly every year around the Azores, studies
about them in mid-Atlantic waters are still scarce [3,4].
The aim of this study is to assess blue whale habitat preferences
and temporal distribution off São Miguel (Azores).
Sightings and photos analyzed were collected between May
2008 and December 2014 from commercial tours of awhale
watching company off the south coast of São Miguel (Azores)
(fig.3). Blue whales presence/absence Generalized Additive
Models were developed using as absences the sightings of the
other species (binomial distribution, k=4). Environmental variables
included bathymetry [5], slope and distance to the coast, and
daily remotely sensed variables [6] (chl, SST, SSH).
99 Blue whale sightings over 7603 of 20 cetacean species were
recorded between March and June,but 1 in September (Fig.1).
Blue whales seen in spring during their north
migration. Other possible route to the S??
Fig.1. Temporal distribution. 2008 sightings were recorded only with photos.
GAM results (fig.4) indicate blue whales’ preference for
deep and cold waters, further than 10km from the coast, and
low SSH related with cyclonic eddies and thus, probably with
local upwelling events, after some chlorophyll depletion.
DEPTH DISTANCE TO
THE COAST
CHLOROPHYLL
SST
daily average
SSH
1Department of Applied Physics, Vigo University, Vigo, Spain.
2Futurismo Azores Whale Watching, Ponta Delgada, São Miguel, Azores.
Fig.4. GAM results for blue whale habitat preferences.
88 photo identifications with 3interannual resightings were
found (Fig.2).
1st sighting : 13/03/2012. Re-sighting: 17/04/2014
1st sighting : 13/03/2012. Re-sighting: 19/04/2014
88 id. Long-term travelling companions?
New dynamic oceanographic variables (mesoscale
circulation features) into the models.
[1] Doniol-Valcroze et al. (2012). Endang Species Res,17(3), 255-268. [2] Pike et al. (2009). NAMMCO Sci. Publ. 7:19-29. [3] Silva et al. (2013). PLoS ONE 8(10) [4] Visser et al. (2011). Mar. Ecol. Prog. Ser. 440: 267-279.
[5] GEBCO_08 Grid, version 20091120, http://www.gebco.net [6] Copernicus Marine Service Products 2015, http://marine.copernicus.eu/
Corresponding author: lauragonzalez@uvigo.es
Fig.3. A) Blue whale sightings
over the bathymetry map of
the study area.
B) Density map.
A) B)
Sightings in 2014 2013 2012 2011 2010 2009
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