Island-wide Transect Survey

A line-transect survey utilising Distance sampling methodologies (Distance sampling methodologies) will provide abundance estimates and map distribution island wide for all inshore cetacean species encountered during the study within 10km from shore.

Platform

Results from a pilot survey carried out in 2014 (Pilot 2014 design and Pilot 2014 results), pointed out that dolphins were strongly attracted to the research vessel, which violates one of the key line-transect method assumptions, that animals do not respond to the survey platform before they are detected by the observers. If this assumption is not met density estimates will be positively biased, resulting in numbers up to six times higher than when the response movement is not taken into account (Cañadas et al., 2004).

To minimize dolphin attraction, an aerial-based survey was planned using a 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 is owned by the Falkland Islands Government Aerial Service – FIGAS (www.fig.gov.fk/figas).

The survey was carried out flying at 150 m of altitude and at 90 knots of speed (about 167 km/hour).

The FIGAS Britten-Norman BN-2B Islander, Bravo-Oscar, used for the aerial survey.

Study area and survey design

The study area measures 19,314 km2 and covers the waters within 10km from the main two islands (East Falkland and West Falkland) as well as the 778 smaller satellite islands with the exception of Beauchêne Island lying about 54 kilometres south the main Islands. The study area was divided in 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 and generally oriented perpendicular to the coast north-south were generated by the software Distance 6.2. Overall, the total length of the designed transects was 4,317 km. Accordingly, the estimated time to survey the planned transects, considering transfer time (to and from airports and from transect to another), is 52 hours divided in 9 days.

For the data collection protocol used, see HERE.

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.

Preliminary results

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. A map with the routes covered and sightings of the two target species is shown in below. Results will be available soon.