Durante le nostre uscite in mare non è sempre facile distinguere la Balenottera comune (Balaenoptera physalus) dalla Balenottera boreale (Balaenoptera borealis).
Sebbene la Balenottera comune sia in generale notevolmente più grande di quella boreale, vediamo spesso animali ancora giovani e, quindi, non ancora completamente cresciuti. A complicare le cose, nei misticeti (i cetacei con i fanoni) le femmine sono più grandi dei maschi, ma non è facile stabilirne il sesso osservandole dalla barca. Non è perciò raro incontrare balenottere comuni e boreali di lunghezza e massa corporea comparabili, a seconda dell'età e del sesso.
Come è possibile, allora, distinguere queste due specie?
Caratteristica unica della Balenottera comune è il colore bianco in corrispondenza della mandibola destra, che è chiaramente distinguibile dal grigio uniforme della 'guancia' sinistra e dal grigio uniforme di entrambi i lati delle Balenottere boreali. 

 

C'è un animale leggendario, che anima la fantasia di grandi e piccini come e più dei giganteschi dinosauri di Hollywood.
A differenza dei dinosauri, però, si tratta di un animale che è possibile incontrare in carne e ossa, dato che la Balenottera azzurra, l'animale più grande che sia mai esistito sul nostro pianeta, vive ancora nei nostri oceani rivelandosi ai curiosi ed emozionatissimi 'whale watchers' con un soffio che può superare i 9 metri di altezza.

Il soffio della Balenottera azzurra (Balaenoptera musculus)

Oltre che per la considerevole stazza e per l'altezza del soffio, la Balenottera azzurra è facilmente distinguibile dagli altri misticeti per via dei riflessi azzurrognoli sul dorso e per le modeste dimensioni della pinna dorsale (vedi foto di sotto).

 
L'inconfondibile dorso e pinna dorsale della Balenottera azzurra   

Qui alle Azzorre, nell acque intorno all'isola di Pico, è molto raro che una Balenottera azzurra mostri la coda prima di immergersi ed è proprio per questo che siamo particolarmente felici di aver assistito a tale evento, per ben due volte, durante l'uscita di Whale Watching di ieri mattina.

Ecco le foto dell'intera sequenza di immersione:

Come in tutti i misticeti (i cetacei con i fanoni), le Balenottere azzurre femmine sono più grandi dei maschi. Sebbene ciò possa apparire come un'anomalia nel dimorfismo sessuale, da un punto di vista evolutivo questo ha un senso. In inverno, infatti, le balenottere migrano verso latitudini più basse, dove danno alla luce e allattano i propri piccoli.
Le acque tropicali e subtropicali, benché calme e termicamente più confortevoli per i nuovi nati, sono in generale poco produttive. La radiazione solare stratifica la colonna d'acqua, limitando la possibilità di riciclo dei nutrienti. Come risultato, le mamme balenottere si trovano ad affrontare lo sforzo del parto e dell'allattamento proprio nel periodo dell'anno in cui possono nutrirsi di meno o non si nutrono affatto. Non deve perciò sorprendere che la selezione naturale abbia privilegiato femmine di grandi dimensioni, in grado di affrontare il titanico sforzo della maternità senza subirne un deperimento irreversibile.
Questo è davvero titanico - un piccolo di Balenottera azzurra può bere circa 400 litri di latte al giorno!

Una cascata d'acqua dalla coda di una Balenottera azzurra

La stagione dei giganti continua e, come diciamo sempre, l'oceano è il luogo dove è lecito aspettarsi l'inaspettato.
A presto qui sul Blog di CW Azores ;-)

Have you ever wanted to see a Blue whale; to hear it blow and smell its breathe?

Follow this sequence of photographs; observe, watch and wonder...

Identification of Fin whales Balaenoptera physalus and Sei whales Balaenoptera borealis, the two baleen species we see most frequently, is not always easy. Separating individuals of the two species travelling together is not straight forward. The largest Fin whales are always bigger than the largest Sei whales but we do not always encounter full grown animals or the largest individuals. Males of both species are appreciably smaller than the females too. We may therefore encounter individuals of either species in a variety of sizes depending on their age and sex. For example it is very possible to encounter a large female Sei whale travelling in loose association or even close proximity to a small male Fin whale.

So how do we recognise each species? Well this is partly down to picking out one key feature of Fin whales that is never shown by Sei whales and, when this cannot be detected, using something many birdwatchers will be familiar with - something called 'jizz'. This is actually an acronym for General Impression of Size and Shape. 'Jizz' can be a very useful tool as each species shows a variety of traits and behaviours shown less or very infrequently by the other. Picking out these features in an animal can be sufficient to identify the species. There are, however, sightings that we can never be sure of their identity.

The key feature of Fin whales that is not shown by Sei whales is the colour of their lower jaw on the right hand side. This is always white in Fin whales and black/dark in Sei whales (see photos below). It has to be the right side too. The lower jaw on the left side of Fin whales is also dark.  

March ends, April begins and with each passing day the sun grows more strong. Plankton has begun to bloom and life in the ocean explodes into activity. This is the season of the giants and with growing anticipation we have been waiting for the great whales to pass these isles. On 30^th our patience was rewarded. During the morning when our boat was already at sea watching Sperm whales our vigias voice crackled excitedly over the radio. He had seen tall blows. This could mean only one thing – baleen whales.

Guided by the vigia we sped off in their direction. Once in the zone we soon caught sight of several blows and it was clear that more than one whale was present but what species? Initially the whales eluded us, surfacing only once or twice to catch a breath before submerging and disappearing from view again. However, soon enough each whale revealed itself. With quite prominent but swept back dorsal fins, broad backs and white under-jaws on their right sides these were Fin whales Balaenoptera physalus (see photos below). Four were present and they appeared to be travelling in two pairs. For awhile we follow one of them. Then surfacing unexpectedly on our starboard side we see a fifth smaller whale. It was pale grey, mottled and had a tiny dorsal fin. It could be only one thing – a young Blue whale Balaenoptera musculus.

 
As the Fin whale surfaces to breathe we get good views of its white under-jaw (on its right side), the twin blowhole and its broad back.

A great start but it is not only a season for giants. Now is also when we see many of the resident dolphins give birth and breed. Recent trips have encountered newborn Bottlenose dolphins Tursiops truncatus, Common dolphins Delphinus delphis and Risso´s dolphins Grampus griseus. Although new born calves of these species can be seen virtually at any time of year, here we see a clear peak in births at this time.

 
A mother Risso's dolphin passes close to shore, on the south side of Pico. The tiny dorsal fin of her newborn calf is clearly visible against her own tall, falcate and heavily scarred fin.

Recently the Common and Bottlenose Dolphins have been especially plentiful, particularly inquisitive and exuberant. They have been showing much social and sexual behaviour as increasing numbers of new calves appear.

 
Here Common and Bottlenose dolphins make close passes of our boat.

If that was not enough yesterday morning we had 'the icing on the cake'- Orcas Orcinus orca. Two, perhaps three mother and calf pairs lingered close to shore. Again on the south coast of Pico. Orcas are rarely seen here and there presence sent a buzz around the whale watching community. Three females were definitely seen but we were only sure of seeing two calves.

The unmistakeable profile of an Orca. Two perhaps three mother calf pairs were present. One female repeatedly tail slapped the water whenever she surfaced to breathe (see below).

Oddly too, we have been seeing Loggerhead turtles Caretta caretta during virtually every trip. This is unusual. Perhaps the ocean currents have been kind to us and have concentrated their numbers around the archipelago.

 
A loggerhead turtle feasts on a Portuguese-man-o-war. Sightings of these sea turtles have been common place.

Despite this bonanza of activity, there are some who remain unmoved. The local Cagarro or Cory´s shearwater Calonectris diomedea, pictured below, slept on unfazed by the Orcas, least of all by our passing boat. I guess as an experienced ocean wanderer it has seen all this before and no doubt much more besides.

 
Unfazed by all the commotion this Cory's shearwater sleeps on.