09 January 2007

Dolphins of the Ionian Sea

this article was written on April 15th, 2006, during the first Earthwatch expedition managed by the Tethys team in the Amvrakikos Gulf, Greece

It is mid April in Vonitsa, a very quaint village on the southern shore of the Amvrakikos Gulf. We have been surveying the Gulf for five days and have sited dolphins in groups ranging from two to six, but the sea conditions have been quite temperamental. Above sea state 3 it is very difficult to spot emerging dorsal fins with the naked eye. However, today we head out in our NovaMarine RIB at 08.30 hrs to our most easterly transect in glass-like waters with the sun shining over the mountainous landscape.

Seconds after reaching our transect starting point, Silvia Bonizzoni, Research Team Member, shouts ‘OUT, 11 O’CLOCK!’. A dorsal fin has been spotted approximately 100 metres from our boat. The PI, Joan Gonzalvo, takes a GPS reading of the first sighting and then approaches the dolphin spotted. The team gets prepared to start recording data. Marisa, HSBC fellow from Brazil, has the electronic NetPad ready to start inputting dolphin behaviour; Helen, US volunteer, is handed the stopwatch to try and time the longest dolphin dive; her daughter Jena, and I are positioned to spot any other surfacing dolphins and Marcia, another HSBC fellow from Brazil, is ready to log our GPS location every minute.

At closer range we spot many dolphins; ‘OUT, 3 O’CLOCK - TWO’, ‘OUT, 7 O’CLOCK – FOUR’, ‘OUT 12 O’CLOCK – THREE ADULTS, ONE JUVENILE’. We are quickly surrounded by these beautiful creatures and the team tries its best to estimate a total group size, but struggles to stay with our focal group, as the dolphins merge in and out of clusters. We estimate over 30, mostly adults but we also spot some juveniles and calves. Some fins are easily recognizable, with many nicks or clear white markings. Silvia and lead PI, Giovanni Bearzi, have been studying the photo-id of these animals for 5 years and easily recognize some of them as they emerge. Ones with very distinctive marks have been affectionately named, such as Pita, who has had the tip of his dorsal fin chopped off, and Elikas (meaning propeller in Greek), who has a large gash behind its dorsal fin from having had an accident with a boat propeller, possibly from bow riding.

The timer rings after 5 minutes and it is time to start recording the dolphins’ behaviour. Some surface feeding is happening which explains the large flock of seagulls crying above our heads. The gulls often follow the dolphins and therefore can act as good indicators when surveying for cetaceans. Some individuals become curious and start to approach our boat, the team becomes very excited as a few begin to bow ride, turning on their sides as they approach to get a better look at us looking at them. In the distance, some are showing signs of social behaviour by leaping great distances out of the water together, and occasionally we see and hear percussive behavior as they belly flop on their sides against the surface of the ocean. With so many dolphins it is hard to keep up with all of the interactions and activity that is occurring but it produces an unforgettable experience for all onboard.

Throughout the hour of recording behaviour and counting group size, Joan has been busy capturing photo-ids of the surrounding dolphins. There is a real art to capturing that perfect picture. The light has to be right, there can’t be too many splashes to hide the markings of the fins, and the best shot is when you catch them leaping with dorsal fin and belly in view, so that you are able to sex the animal later. You can never tell if you have taken the perfect shot until you analyse the photos when you return, so Joan continues to photograph all emerging fins and finishes with 210 images.

We stop survey at 12.00 hrs and start to return back to base after an action packed and awe-inspiring day. The next step after lunch is to crop all of the photos and try to match them against an existing catalogue of individuals. This can be a time consuming but rewarding task when you identify your animals seen that day.

The day ends with a delectable dish prepared by the Brazilian fellows, some authentic Greek wine and sweets. The group camaraderie makes the whole experience even more enjoyable, with wonderful discussion of the day’s events.

We have another early rise tomorrow at 07.00hrs so everyone heads to bed and falls asleep listening to the friendly local Greek villagers enjoying their small town night life on a Saturday night. It is hard to believe that there is only one more survey day left.

Jen Alger

For more information on Earthwatch expeditions click here

04 January 2007

Di che tursiope si tratta?

Nella letteratura scientifica si parla spesso di tursiopi (in inglese ‘bottlenose dolphins’), ma a volte non è chiaro a che specie ci si riferisca.

Di tursiopi infatti ne sono state riconosciute (finora) almeno due specie: il Tursiops truncatus (common bottlenose dolphin) e il Tursiops aduncus (Indian-Ocean bottlenose dolphin). In italiano il primo è chiamato semplicemente ‘tursiope’, il secondo ‘tursiope indo-pacifico’, anche per il fatto che in Mediterraneo vive solo la prima specie.

Quando si ha a che fare con articoli pubblicati qualche tempo fa, prima che avvenisse questa divisione tassonomica, è a volte difficile capire di che specie si stia parlando. Sono infatti quasi tutti ‘bottlenose dolphin’ Tursiops truncatus.

Di questi animali viene spesso magnificata la grande adattabilità e flessibilità di comportamento, organizzazione sociale, dieta etc. Si tratta effettivamente di animali molto opportunisti e di abitudini elastiche, ma a rigore, trattandosi di due diverse specie, non è corretto mettere insieme i comportamenti dei tursiopi italiani con, ad esempio, quelli studiati a Shark Bay, in Australia. I secondi appartengono infatti alla specie aduncus.

Una certa tendenza a mantenere lo status quo da parte di tanti ricercatori, ignorando alcune recenti scoperte a favore della ‘tradizione’, fa sì che si continui a discutere di tursiope come se ne esistesse una sola specie. Eppure, i motivi per abbandonare il vecchio per il nuovo ci sarebbero.

Già una decina d’anni fa Richard G. LeDuc ha dimostrato che esistono differenze sostanziali all’interno del genere Tursiops, e che tale genere è sicuramente polifiletico. In altre parole, LeDuc, insieme ai suoi colleghi Barbara E. Curry e William F. Perrin, sostengono che all’interno del genere esistano diverse specie, e che il genere necessiti di una revisione sostanziale.

E’ interessante notare che non si tratta solo di un puntiglio da superspecialisti, destinato a restare oggetto di uggiose disquisizioni accademiche. La specie Tursiops aduncus, infatti, risulterebbe più simile al genere Stenella di quanto non lo sia al genere Tursiops. Potrebbe quindi trattarsi addirittura di una Stenella aduncus!

Quali che siano le future suddivisioni tassonomiche, alcune organizzazioni autorevoli (ad esempio l’International Whaling Commission - IWC- e la World Conservation Union - IUCN) hanno già adottato la tassonomia aggiornata accettando le due specie truncatus e aduncus.

E' probabile che nel prossimo futuro spunteranno altre specie o sottospecie, data la grande variabilità morfologica, genetica, molecolare etc. che si riscontra nelle diverse popolazioni di tursiopi che abitano le acque temperate e tropicali di tutto il Pianeta.

Si vede quindi quanto sia inopportuno mettere in uno stesso contenitore i tursiopi di Shark Bay, che usano le spugne come strumenti e formano ‘bande’ di maschi note per segregare le femmine e costringerle all’accoppiamento, con i tursiopi nostrani, che certe cose (a quel che risulta) proprio non le fanno.

Giovanni Bearzi

Per approfondimenti:

Cetacean taxonomy and common names

Leduc R.G., Curry B.E. 1997. Mitochondrial DNA sequence analysis indicates need for revision of the genus Tursiops. Report of the International Whaling Commission 47:393.

LeDuc R.G., Perrin W.F., Dizon A.E. 1999. Phylogenetic relationships among the delphinid cetaceans based on full cytochrome b sequences. Marine Mammal Science 15:619-648.