Frontiers in Marine Science (Jun 2014)
Looking for North Atlantic Baleen Whales: When are they coming to the Azores?
Abstract
The archipelago of the Azores is like an oasis in the middle of the Atlantic Ocean. Surrounded by deep waters, those islands are a “must stop” place for every traveler, including, of course, cetaceans. Around the archipelago more than 24 different species of whales and dolphins can be seen. Some of them are resident such as the common dolphin or the emblematic sperm whale. But others are seasonal or sporadic, such as the spotted dolphin or the big baleen whales. The aim of this study is to assess the temporal distribution of the baleen whales sighted off Azores. We analyzed data gathered off the south coast of São Miguel (Azores) from 2006 to 2013 from whale watching vessels. The whale watching company is located in Ponta Delgada and it works all throughout the year, always when the weather, the sea state and the number of tourists allow doing it. In Azores, whale watching companies use to locate cetaceans from land, with specialized lookouts spotting the animals from strategic points on the shore (as whalers did). These lookouts use powerful binoculars to locate the animals, and then give instructions to the boats to get to them. Once there, the boat registers date, hour, sea state, visibility, position (GPS), species, number of individuals, number of adults, juveniles and calves, behavior, association with other species and if there are other boats in the area. Photos are taken whenever it is possible and they are analyzed when the quality is good enough to distinguish natural marks and shapes. Most of the photos used in this study were taken in the last 5 years. Photo-Id catalogues were created for blue whales, fin whales and humpback whales. Data collected are more complete and frequent since 2009. In this case we have analyzed a total of 7691 sightings, belonging to 20 different species of cetaceans, 14 Odontoceti and 6 Mysticeti. In the latter group we recorded 491 sightings. The three most sighted Mysticeti species were the three great baleen whales: fin whale (Balaenoptera physalus) with 221 sightings, sei whale (Balaenoptera borealis) with 143 and blue whale (Balaenoptera musculus) with 83. Those three species were sighted regularly each season every year of the study. Following them, with a much smaller number of sightings, were minke whales (Balaenoptera acutorostrata) with 16, humpback whales (Megaptera novaeangliae) with 15 and Bryde’s whales (Balaenoptera edeni) with 13. Minke, humpback and Bryde’s whales were seen more rarely, being occasionally observed around the islands. The preferred time of the year for all species except Bryde’s, were spring months between March and June (81.7% of the sightings). Blue whales were more frequent in 2010 and 2012, having the highest sighting rates in May (32 sightings), April (24 sightings) and March (20 sightings), making up 91.6% of total blue whale records. Having into account March 2014 photos, we identified 75 different blue whales, and from those, only two were re-sighted in different years. One was firstly sighted on April 2010 with a calf and re-sighted alone on March 2014; and the other was firstly sighted on March 2012 and re-sighted on April 2014. 2013 was a good unusual year for fin whales, with a total number of 90 sightings seen mostly in may. Along the study period, we identified 45 fin whales, and at the moment, we didn’t get any match in different years or locations. Humpback whales were not sighted during 2006, 2007, 2008 and 2013, but we must bear in mind that our data from those years are incomplete (except for 2013). Nevertheless, they seem to have a slight preference for April-May as well. We photo-identified 12 individuals. One whale was re-sighted after only seven days, but there were no other re-sightings between seasons or years yet. For sei whales the best year was 2010, with 47 records. Most of records for both species were made in April and May, 66% of the fin whales and 54% of sei whales. Minke whales were sighted all years but 2007 and 2008. They don’t present any seasonal pattern, as they were seen in March, April, July, August and November. Bryde’s whales were sighted only in 2009 and 2013, and in both years were seen in summer (end of July-August). According to these findings we can conclude that fin whales, sei whales and blue whales are seasonal visitors in the Azores, as they are observed every year mainly in spring months between April and May. Those results agree with the hypothesis that great North Atlantic baleen whales (blue, fin and sei whales) are migratory [Olsen et al., 2009; Silva et al., 2013; Visser et al., 2011]. They pass off Azores mainly during spring months while they are travelling from their breeding grounds in low latitudes to their feeding grounds in the North Atlantic. However, if they are returning southwards to spend the winter, they have not been observed, so, if they do, they probably follow a different route. As a result, we believe that at least some blue whales usually pass along the Azores probably while they are moving to the North Atlantic feeding grounds. We have recorded two re-sightings of this species in different years, in the same area (south off São Miguel) and same time of the year (1 month lag). In another hand, we observed that minke whales, humpback whales and Bryde’s whales are only occasionally sighted around the islands. Minke and humpback don’t seem to have any preference of season, while Bryde’s were seen only in summer according to previous findings that suggest a temporal range expansion of the Eastern Atlantic population [Steiner et al., 2008]. To comprehend the occurrence of these marine mammals off Azores it would be interesting to better understand their migration and evaluate its relationship with oceanographic characteristics such as temperature, chlorophyll, currents and even geomagnetism. Next steps will be aimed at searching for these relationships and comparing our catalogues with others in the Atlantic in order to find new insights into the migration of baleen whales in the North Atlantic.
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