Eighth International Aerial Survey of Cetacean and Sea Turtle Abundance in the Adriatic Sea

Eighth International Aerial Survey of Cetacean and Sea Turtle Abundance in the Adriatic Sea

An international aerial survey of cetaceans and sea turtles is currently under way, covering the entire Adriatic Sea. The aim of the survey is to determine the abundance and distribution of protected marine species and to collect the data needed to assess their conservation status and monitor long-term changes in marine ecosystems.

The Eighth International Aerial Survey of Cetacean and Sea Turtle Abundance in the Adriatic Sea began on 31 July 2026. The research team carried out its first survey flights over the Strait of Otranto and the southern Adriatic, operating from Brindisi Airport, where the team was based for the first three days of the survey. The team then relocated to Dubrovnik, from where survey flights over the southern and central Adriatic continued. To date, the team has completed a total of 40 survey flights over the Adriatic. Due to a forecast change in weather conditions, the research aircraft is currently on Lošinj, from where the survey will continue over the northern Adriatic.

The survey in the Adriatic is being conducted by a team of scientists coordinated by the Blue World Institute and Blue World Vis, with the participation of scientists from the Croatian Natural History Museum. The survey coordinator for the Adriatic is Associate Professor Draško Holcer, PhD, of the Croatian Natural History Museum. The research team also includes Assistant Professor Grgur Pleslić, PhD, of the Blue World Institute and Maša Frleta-Valić, MSc in Ecology, of Blue World Vis.

“We conduct the survey in accordance with an internationally accepted aerial survey methodology. The aircraft follows predetermined survey lines, which in the Adriatic are spaced 15 kilometres apart, and whenever animals are sighted, their distance from the survey line is determined. During data analysis, abundance is estimated within the areas covered by the researchers, after which the final total abundance for the entire survey area is calculated. The use of a standardised method ensures systematic coverage of the entire Adriatic and the collection of comparable data throughout the survey area,” says Dr Holcer.

The Croatian part of the survey is being carried out as part of the project “Nature under Observation – Monitoring the Conservation Status of Species and Habitat Types”, implemented by the Ministry of Environmental Protection and Green Transition and the Institute for Environment and Nature, with co-financing from the European Union. The project contributes to fulfilling the Republic of Croatia’s obligations under the Habitats Directive (HD).

The Italian part of the survey is being conducted by ISPRA as part of the official national monitoring programme under the Marine Strategy Framework Directive (MSFD) and the LIFE MareNatura project, led and coordinated by Mr Giancarlo Lauriano of the Italian Institute for Environmental Protection and Research (ISPRA).

Both national programmes contribute to Croatia’s and Italy’s international obligations under the ACCOBAMS Agreement and the ACCOBAMS Survey Initiative (ASI). ASI is an international initiative of the Agreement on the Conservation of Cetaceans of the Black Sea, Mediterranean Sea and Contiguous Atlantic Area (ACCOBAMS), through which data on the abundance and distribution of cetaceans and other large marine vertebrates are collected in a coordinated and simultaneous manner across the entire Mediterranean and Black Sea regions. This year marks the second implementation of the initiative.

“During July and August, surveys under the ASI II programme are being conducted throughout the Mediterranean Sea. Given the specific characteristics of individual areas and the need to determine the abundance and presence of certain species that occur in low numbers in the Mediterranean, such as sperm whales or Cuvier’s beaked whales, aerial surveys are occasionally combined with vessel-based surveys that record whale vocalisations. This year, in addition to participating in the Adriatic survey, I also took part in aerial surveys in the Ionian Sea conducted during July,” says Ms Frleta-Valić.

The Blue World Institute, ISPRA and the Croatian Natural History Museum have been collaborating on aerial surveys since 2010, when the first aerial surveys of the entire Adriatic Sea were conducted, followed by repeat surveys in 2013. For the first time, these surveys made it possible to estimate the abundance and distribution of bottlenose dolphins (Tursiops truncatus) and other cetacean species across the entire Adriatic, laying the foundations for the long-term monitoring of these protected species.

“Our insistence on conducting a joint survey of the entire Adriatic is based on the fact that large marine vertebrates do not recognise national borders. Dolphins we encounter on the Croatian side today may already be in Italy tomorrow. Conducting multiple separate monitoring programmes across the Adriatic would significantly undermine our understanding of actual changes in abundance and patterns of habitat use,” adds Dr Holcer, who has led these surveys since their inception.

Following a similar approach, the first survey covering the entire Mediterranean was conducted in 2018 as part of the ACCOBAMS Survey Initiative (ASI-1), which also included the Adriatic. In 2019 and 2020, additional surveys of the northern and central Adriatic were carried out as part of the LIFE Euroturtles project, while in 2021 and 2022 the surveys once again covered the entire Adriatic Sea.

“Thanks to the continuous series of surveys carried out since 2010, the Adriatic Sea today represents the area in which the abundance and distribution of cetaceans and sea turtles are the best monitored in the entire Mediterranean, primarily due to the large number of surveys conducted and the extensive total area covered by research flights,” stated Dr Pleslić.

The data collected during this survey will contribute to national monitoring programmes, international reporting and regional analyses within the ASI-II initiative. Together with the results of previous surveys, they will enable continuous monitoring of population status across the Adriatic and the entire Mediterranean and contribute to more effective protection and management of marine species and ecosystems.

The Blue World Institute of Marine Research and Conservation is a Croatian non-profit, non-governmental organisation based on the island of Lošinj. Our work covers the entire Adriatic Sea, with a primary focus on the study of large marine vertebrates – cetaceans, sea turtles and cartilaginous fish. Our activities aim to conserve marine biodiversity, raise public awareness, protect the marine environment as a whole and promote sustainable development. We strive for excellence through our three core programmes – research, education and conservation.

BLUE WORLD INSTITUTE OF MARINE RESEARCH AND CONSERVATION
Kaštel 24, 51551 Veli Lošinj
info@plavi-svijet.org
Tel: +385 51 604 666

Authors
Draško Holcer, PhD