Photo-identification boat cruises targeting bottlenose and common dolphins were conducted in the Dzharylgach Bay, at depths between 5 and 9 m, and the sea area of the Karkinit Bay near the Dzharylgach Island, at depths between 3 and 12 m.
A boat and a yacht used for operations in the Dzharylgach area, summer 2017.
Summary of tracks for four photo identification surveys in the Dzharylgach area, July 2017.
In total, photo-identification boat cruises were conducted between June 23 and August 9, 2017. The total effort was more than 1300 km.
The surveys were recorded, using protocols of effort and of cetacean sightings.
The linear transect survey (LTS) was conducted in the areas 5-8 m deep in the Dzharylgach Gulf (the greatest survey area in 2017 was 116 km2) and 5-14 m deep in the Karkinit Gulf (the greatest area of 143 km2), and the results were separately calculated for each stratum.
The survey platform was the yacht 8.8 m long; two pairs of observers, equipped by binoculars (10×40 and 10×50), changed after 30 minutes, and a dedicated operator recorded the data. The survey was conducted under good weather conditions (sea state less than 2 points of the Beaufort scale, visibility more than 5 km, zero precipitation). Boat speed was on average 9.5 km/h, at maximum 11 km/h. The observer eye height was 2.5 m. Tracks and coordinates were recorded, using the GPS navigator Garmin eTrex 30. Protocols of effort and registrations were filled in during the surveys.
Line transect survey in the Dzharylgach area.
Species, group size, distance and angle from the moving boat were recorded at each encounter. In addition, behaviour types were recorded: fast movement, normal movement, feeding, etc., as well as behaviour in relation to the boat: avoiding, attraction or neutral. Density and abundance, cluster (group) density were estimated by analytical tools based on detection probability functions for distance sampling (Buckland et al., 2001), using Distance 7.0 software.
Harbour porpoises formed groups up to 8 animals, median = 1. They were randomly dispersed both within and outside of the Dzharylgach Gulf. The greatest groups were recorded in the centre of the bay, sometimes approaching the Skadovsk port area. In the Karkinit Gulf the greatest groups occurred south to the Dzharylgach Island.
Sightings of harbour porpoises near the Dzharylgach Island in 2017.
Common dolphins occurred in groups up to 12 individuals, median = 3. The common dolphins strongly tended to the Dzharylgach Gulf, and only few of them were observed in the Karkinit Gulf. The greatest groups were recorded both in the middle and in the easternmost part of the Dzharylgach Gulf, north to and near the tip of the island. There were juveniles and calves in 30% of groups. There were 65 photo identified individuals. At least some of the dolphins were classified as summer residents. There were direct observations of dolphin feeding and courtship behaviour in the eastern part of the Dzharylgach Gulf.
Sightings of common dolphins near the Dzharylgach Island in 2017.
Bottlenose dolphins were recorded in groups up to seven individuals, median = 2. There were juveniles in 27% of sightings. All the sightings were on the open sea side or near the tip and the north side of the island rather than in the Dharylgach Gulf. At least, 27 dolphins were photo identified. A few individuals were re-sighted between two years, 2016 and 2017, and even more within the same year. Most of them were re-sighted at least 4 times. Two of them were re-sighted during both summer periods at the same locality, near the tip and southern side of the island. They showed distinct hunting, game and mating behavior. Therefore, a significant portion of the bottlenose dolphins were classified as summer residents.
Sightings of bottlenose dolphins near the Dzharylgach Island in 2017.
Thus, the sea area near the Dzharylgach Island, including the Dzharylgach Bay, was confirmed as an important summer habitat for all three species of cetaceans.
Gladilina, E. V., Vishnyakova, K. A., Neprokin, O. O., Ivanchikova, Yu. F., Derkacheva, T. A., Kryukova, A. A., Savenko, O. V., Gol’din, P. E. 2017. Linear transect surveys of abundance and density of cetaceans in the area near the Dzharylgach Island in the north-western Black Sea. Vestnik zoologii, 51(4): 335–342.