Habitat preference and subgroup association of the common bottlenose dolphin in the Aegean Sea

Bc. Nikola Semeráková

Master's thesis

Abstract:

The Mediterranean subpopulation of bottlenose dolphins (Tursiops truncatus) is vulnerable, according to the International Union for Conservation of Nature Red List (IUCN). Due to its coastal habitats, this species is endangered by cumulative stressors, human activities, and other escalating pressures. Photo-identification (photo-ID) method was used to identify and create a catalogue of dorsal fins of bottlenose dolphins and provide evidence about the distribution of habitat preference and groups association between the summer (April – September) and winter (October – March) seasons. The photo-ID dataset was collected during boat surveys year-round between January 2015-August 2021 in the eastern Aegean Sea. A geographic information system (QGIS) was used to illustrate sightings of identified dolphins between seasons and group size within bathymetry distribution. Over seven years, 500 dedicated boat surveys with 22,300 km of active search effort (Beaufort sea states ≤3) were conducted, and 131 bottlenose dolphins were documented and subsequently resighted in the photo-ID catalogue based on their dorsal fins. The encounter rate of sighted bottlenose dolphins was 2.6 dolphins per 100 km and 1.4 photo-identified bottlenose dolphins per 100 km. The main objectives were to investigate the influence of environmental variables (bathymetry, distance from shore, sea surface temperature, salinity, chlorophyll) on bottlenose dolphins' distribution and group size during seasons (summer and winter). The Mann-Whitney U test showed that environmental factors (bathymetry, distance from shore, sea surface temperature, salinity) significantly influenced the distribution of bottlenose dolphins between seasons, except for chlorophyll concentration. The mean group size was 6.23 individuals, ranging between 1 and 18 dolphins. A Mann-Whitney U test revealed that the group size of identified dolphins was significantly larger during the winter than the summer season. Analysis of a general linear model (GLM) demonstrated no correlation in group size of identified bottlenose dolphins with depth and distance from the coast. The obtained results about habitats and social groups are essential for adequate protection and identifying special management measures, planning, and conservation activities in this study area.

Keywords

Tursiops truncatus, photo-identification, seasonal distribution, group size, encounter rate

Language used: English

Date on which the thesis was submitted / produced: 31. 3. 2022

Thesis defence

• Supervisor: Ing. Miloslav Petrtýl, Ph.D.

Czech University of Life Sciences Prague

Faculty of Agrobiology, Food and Natural Resources

Master programme / field:
Engineering Ecology / Nature Conservation