DOKE provided the first robust estimates of abundance and density of Commerson’s and Peale’s dolphins and baleen whales for the whole inshore Falklands waters.Aerial line-transect surveys utilising distance sampling methodologies (Distance sampling methodologies) were used.
The study area included the water within 10 km from the coast (with the exclusion of Beauchêne Island located 54km southeast of East Falkland). The area was divided into 12 strata accounting for possible differences in physical characteristics with respect to the prevailing winds and currents and the general physiography of the sea bottom. A total of 217 transects spaced between 5 and 6 km apart and generally oriented perpendicular to the coast north-south were generated to obtain a coverage probability of 0.8. Overall, the total length of the designed transects was 4317 km. Accordingly, the estimated time to survey the planned transects, considering transfer time (to and from the airport and from one transect to another) was 52 hours divided in 9 days.
Map of the Falkland Islands showing the study area within 10km from the coastline (divided in 12 strata – see black number with white buffer) and the transects (parallel black lines), obtained with the software Distance 6.2.
The survey platform was the aircraft BRAVO-OSCAR Britten-Norman BN-2B Islander with high-wing, double engine and two bubble windows on the rear allowing observation below the plane itself. The aircraft flew at an altitude of 150 m and a speed of 90 knots (~167 km/hour).
The FIGAS Britten-Norman BN-2B Islander, Bravo-Oscar, used for the aerial survey.
The research crew consisted of a data recorder and two observers. The data recorder was positioned near to the pilot; the observers were seated at the bubble windows to the rear of the plane. The researchers rotated positions in the plane according to the instructions of the data recorder, ideally every hour, and during off line effort.
Data Recorder, located on the front, near the pilot
Observers, located on the rear looking down at the the bubble windows
Observers using a chronometer to measure the angle abeam from which the perpendicular distance between the transect line and the cetacean observed will be calculated
The aerial survey was carried out on the days 18th, 19th, and 25th of March, 2nd, 6th, 9th, 17th and 23rd of Aril 2017 and 8th of May 2017.
The total number of sightings was 454 including seven species: Commerson’s dolphin (238 sightings), Peale’s dolphin (60 sightings), sei whale (74 sightings), fin whale (12 sightings), common minke whale (2 sightings – species identified by the presence of the white patch on the right pectoral fin), blue whale (2 sightings), and southern right whale (1 sighting). The remaining 65 sightings were recorded as unidentified baleen whales of which 62 were labelled as possible sei whale. Average group size in shown in Table 1.
Table 1. Species/group sightings, number of individual, group size and range made during the aerial survey.
Species | Sightings numberA | No of individuals | Group size | Standard deviation | Range |
Commerson’s dolphin | 238 | 1,082 | 4.57 | 6.17 | 1-70 |
Peale’s dolphin | 60 | 264 | 4.47 | 4.27 | 1-21 |
Sei whale | 74 | 95 | 1.28 | 0.63 | 1-4 |
Fin whale | 12 | 14 | 1.17 | 0.39 | 1-2 |
Common minke whale | 2 | 2 | 1.00 | ||
Blue whale | 2 | 2 | 1.00 | ||
Southern right whale | 1 | 1 | 1.00 | ||
Unidentified baleen whales | 65 | 80 | 1.23 | 0.52 | 1-3 |
Tot | 454 | 1,541 |
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The positions of the sightings for each species/group are shown below.
Sighting of Commerson’s (red triangles) and Peale’s dolphins (blue squares) during the aerial surveys (including navigation between transects) carried out from March to May 2017.
Sightings of baleen whales during the aerial surveys (including navigation between transects) carried out from March to May 2017.
The first ever systematically obtained estimates of abundances are the follows:
The few sightings of blue and southern right whales occurred during transits/ off effort legs or too far from the trackline and were thus not included in the analyses.
Abundance estimates are likely to be underestimated due to the fact that availability bias (i.e. the amount of time animals are available to be seen at the surface) has not been yet included in the analyses.
The project is funded by the Darwin Initiative through the UK Government
