Bottlenose dolphins off Croatia
Losinj bottlenose dolphin community
A resident group of bottlenose dolphins inhabiting the area of Kvarneric, and in particular the eastern side of Losinj and Cres islands in the northern Adriatic Sea, is one of the best studied community of dolphins in the Mediterranean Sea. The research, started in 1987 by Tethys, is continued by Blue World since 2000.
This individual, nicknamed Belugo, has been seen around Losinj over the past
two decades and may be over 30 years old. Photo © Blue World.
The photo-identification catalogue of dolphins currently holds over 200 individuals. Many of these are regularly re-sighted, indicating a high level of year-round site fidelity, although their range is considered greater than the main study area. The community initially estimated at around 120 individuals, during the last decade faced a decline and is now estimated to be around 100 animals.
A number of different studies on this group of bottlenose dolphins have been carried out including the analysis of their distribution and habitat use; their behavioural budget, diet, growth and reproduction; a comparison of skin abnormalities, deformities and injuries with 9 other populations worldwide; preliminary assessment of fish resources utilised by fishermen overlaps with dietary needs of the bottlenose dolphins; and impact of boat disturbance and ambient marine noise on dolphin behaviour and distribution. Each of these studies in comparison to similar studies worldwide showed a remarkable adaptability of bottlenose dolphins to their environment and a form of “local culture”.Distribution of bottlenose dolphins of the Kvarneric was assessed through boat-based surveys and photo-identification techniques. Between 1995 and 2003 a decline in abundance of 39% was observed, which aroused great concern.
This observation was exacerbated by changes in habitat use caused by the increasing number of pleasure boats within the newly-created (but not yet enforced) Losinj Marine Protected Area. The apparent survival rate of adults was estimated to be significantly lower than for any other bottlenose dolphin populations in the world. In addition, first-year calf survival was low, and a decreasing trend in fecundity rate was observed.
Population viability analyses indicate that the current rate of human-induced mortality is unsustainable. The chance of local extinction risk within the next three generations was estimated to be high (35%). According to the IUCN Red List Criteria, the Kvarneric population should be listed as Endangered.
The Losinj community is threatened by the planned development of unregulated mass tourism, and by the related disturbance and noise pollution resulting from coastal construction. Unregulated boating was identified as one of the main reasons behind the observed decline in numbers, and dolphins abandoning this area. Other threats include declining prey resources and pollution.
Bottlenose dolphins are the only regular cetacean species in the Losinj and Cres archipelago. In recent times, three other species have been recorded occasionally in the area. The short-beaked common dolphin was fairly abundant historically, but now is almost absent. Other species recorded in the area include striped dolphins, Risso's dolphins and fin whales.
Bottlenose dolphins photographed near Losinj, Croatia. Photos © Tethys Research Institute.
Vis archipelago bottlenose dolphin community
Provisional information gathered from opportunistic sightings and strandings point to potential differences in cetacean fauna between the southern and the northern part of the Adriatic Sea. This is most likely related to the strong latitudinal and longitudinal asymmetries in bathymetry and associated habitat types.
In 2007 Blue World started a research project in the Vis archipelago. Preliminary results suggest that this is an interesting area for dolphin studies. Dolphin encounter rate was 0.113 dolphins/km, with a sighting frequency of 0.025 sightings/km in good conditions, i.e. twice that found in the north-eastern Adriatic. The mean group size of bottlenose dolphin groups was estimated at 5.2, ranging from 1 to 14 individuals. Standard photo-identification methods resulted in a catalogue of 89 mature and 26 immature individuals. No matches were found with two other catalogues from the northern and central parts of the Croatian coast.
A fin whale was also sighted once, and several opportunistic reports occurred during the season in the same area.
Maximilian - the first newborn recorded near the Croatian island of Vis.
Photo © Blue World.
Cetacean Alliance investigators:
For more information, see:
Information presented here also based on:
Fortuna C.M. 2006. Ecology and conservation of bottlenose dolphins (Tursiops truncatus) in the north-eastern Adriatic Sea. Ph.D. thesis, University of St. Andrews, UK. 275 pp.
