We have recently had the opportunity to reopen our base on the Northern Aegean Island of Samos, which has been closed since the start of the Covid-19 pandemic. This is an exciting change of pace for Archipelagos, as this marine region is a hotspot for many species of cetaceans, creating unequalled opportunities for boat surveys and studies for our marine mammal team. Since arriving in late June, we have successfully completed boat surveys on a regular basis, including several overnight expeditions to ports of Ikaria and Karlovassi, on the northern side of Samos. Transects on the southern side of Samos have enabled repeated sightings of common dolphins, Delphinus delphis, and bottlenose dolphins, Tursiops truncatus. These surveys allow continued study of natural behaviours, acoustic patterns, and photo identification. We have even been able to identify the same dolphins between multiple boat surveys!
Multiple-day surveys in the Northern parts of Samos have allowed us to study a biodiverse deep-water region, offering fantastic sightings of Risso’s dolphin, Grampus griseus, Cuvier’s beaked whale, Ziphius cavirostris, and striped dolphin, Stenella coruleoalba. It is often unrealised that these species are present in Mediterranean waters, and thus they are frequently understudied and under-protected. We are ecstatic to have the opportunity to glimpse these rare species and to collect data that help us understand their lives better. Our research continues to preserve and protect all species found in the waters surrounding Greece and we will continue to do our best to observe and study the many cetaceans of the Mediterranean.
High quality photos taken by members of Archipelagos marine mammal research team are a crucial component to our studies of Mediterranean cetaceans. We attempt to photograph every individual of any group (pod) of cetaceans we observe while on the water. These photos enable us to separately distinguish individuals by a method called “photo-ID”. Identification is normally enabled by distinctive ‘notches’ found on dolphins’ dorsal fins, as well as differing patterns of colouration, or other scars on the body. We have successfully produced a catalogue of our common dolphin sightings around Samos since we renitiated these surveys in June – with over 50 different individuals! Several of these have been recorded multiple times, with one avid traveller having been seen 8 days apart at locations over 100km away. These results display an incredible ability of Delphinus delphis to travel large distances in short periods of time.
Whilst collating a local catalogue of our recent sightings, we are also analysing the results of boat surveys since 2014 to observe whether individuals can be identified throughout time. This has shown that the same individual has been observed in 2015 and 2021 – 6 years apart! Our catalogues are therefore an essential resource for any long-term study of cetaceans in the Aegean Sea. We continue to work hard on these, and plan to look back through Archipelagos’ incredibly detailed long history of boat surveys, dating back to 2000, to understand what is happening to the regions’ marine mammal populations.
Our team is also busy producing photo catalogues of other species, including Risso’s, striped, and bottlenose dolphins. All of these can be used in important studies of population dynamics, distances travelled, social associations and life history patterns. We look forward to finding more matches and expanding our catalogues with photos from future encounters.
Behaviour and Acoustics
Boat surveys also enable us to study the behaviour and acoustics of cetaceans. These studies utilise technology of various types, including BORIS (Behavioural Observation Research Interactive Software), video recordings and behavioural notations. While viewing dolphins we frequently recognise behavioural events such as bowing, leaping, or boat inspections which can also be related to the longer-term behavioural state, such as feeding, socialising, or travelling. During our most recent boat surveys, we have observed a variety of behaviours from many different species. For example, common and bottlenose dolphins were often found travelling in the Southern regions of Samos and have also been seen feeding along the coast. Through analysing such data, we can begin to understand how cetaceans spend their time and we try to identify key habitats that need protection.
Even when we can’t see cetaceans, bioacoustic monitoring allows us to record their presence with a hydrophone. The frequency and amplitude of dolphin clicks and whistles can be related to stress levels, and we aim to study whether this is related to anthropogenic (i.e. human produced) noise, such as boat activity. The frequency of calls vary amongst species (and even between different individuals – younger dolphins have a higher pitch!), and thus enable the identification of species without the need for above-water identification. This means our use of bioacoustics becomes interdisciplinary with all other research on boat surveys. For example, during one of the surveys over the north Ikaria trench we heard Cuvier’s Beaked Whales’, Ziphius cavirostris, clicks, and when the clicks stopped (because they were no longer diving) we spotted them at the surface and were able to take photographs of them.
By Imogen Dumville