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Abstract:
We followed line-transect distance sampling survey protocols for estimating abundance of Svalbard reindeer in Sassendalen, Svalbard in July 2021.
Rangifer tarandus
Quality
For the distance sampling survey, we allocated 10 transect lines in north-south direction, from the mountain foothills to the riverbanks, on each side of a large river in Sassendalen, Svalbard. We chose one random latitude for the first line and placed additional parallel transect lines systematically apart 2.5 km east or west from this latitude to reduce the potential of overlapping reindeer observations and violation of the assumption of independence for DS surveys. We chose this systematic orientation across the valley (i.e., riverbed to mountain side or vise-versa) to reduce any bias from potential gradients in animal density related to e.g., plant phenology and/or habitat configuration. The strip length of each of the transects varied depending on the length from the mountain side to the riverbank (1.2 km to 2.9 km). The survey was conducted within the same three-day period 14-17 July 2021.
The 10 transects were walked by one observer at a constant speed (2–3 km h-1) without stops, except during measurements. We used a handheld GPS and a compass to keep the line direction, and single reindeer or clusters were detected on both sides of the transect line with the naked eye. When a reindeer or reindeer group was spotted, the observer looked only in its direction until measurements were taken. To respect the assumption of constant detection along the transect line, no scanning of the surroundings was done when stopping to take measurements. Each observation was measured by laser binoculars (10×42 Leica Geovid) to the nearest meter and a compass was used to measure the angle from the observer to the reindeer. Note that this method only captures the total number of reindeer and no structural information on age and does not record the population structure (i.e., age and sex) of the reindeer. The geographic position of the observer was also recorded. For practical reasons using the laser, measurements were taken to the largest reindeer (e.g., a mother rather than her calf) or the middle individual of a group of adults. From the distance sampling survey, the GPS positions of reindeer groups was calculated and used in the final dataset. For further details and application of the method on Svalbard reindeer see Le Moullec et al. 2017, Le Moullec et al. 2019.