The aerial and shipboard observation of polar bears along coastline of Wrangel Island

The aerial and shipboard observation of polar bears along coastline of Wrangel Island

8 February 2013

No reliable assessments of the numbers and status of the Chukchi Sea - Alaska population of the polar bear are available to date (Vongraven and Peacock 2011). In 2005-2009 on the Wrangel Island a census of the polar bears that landed on standard routes in the western part of the island (Ovsyanikov and Menyushina 2010). The numbers of the animals were estimated at 150-600: 150-200 in 2005 and 2006, 550-600 in 2007; 250-300, - in 2008; and 250-300 in 2009. In this case, the number of the animals actually sighted on the island was 104 in 2005, 99 in 2006; 391 in 2007; 200 in 2008; 183 in 2009.


Under the program of the study of the polar bear in the Russian Arctic, an assessment of the numbers of the polar bear in the Russian Arctic on the Vrangel Island was performed in 2010 in the course of the passage of the expedition ship «Mihail Somov ». The ship observations in the region of the village Ushakovskoe were performed on 5-7.10.2010. During the first day, 8 polar bears were recorded on the second day 6, on the third day, 6. For several days, groups of one (occasionally, two) adult individuals and two cubs were recorded, both at the shoreline and on the slope. The flyover of the Wrangel Island was also performed on 8.10.2012. The weather favored the observations except a small area (19 km) of cape Western to Cape Thomas, where due to the strong winds and the low dense clouds the ship had to go farther from the shoreline.


We recorded 115 bears, which were in the coastal zone at a distance of 3-5 km deep into the Island. The greatest number of bears (39) was recorded in the northeast of the island at the spits Bruch, Adrianovv, Chicherin, Mushtakov. On cape Warring, 9 animals were recorded; on Cape Blossom, 23; on the western coast south of the Cape Ptichy Bazaar 12. On Cape Litke and its vicinity (up to 5 km) on the shore west of Bezymyannye Mountains, in the vicinity of the river Neozhidannya, in the western Krasin Bay between Cape Hawaii and Cape Utes Bolshevika, no bears were sighted. A large numbers of single bears were sighted in the northwest of the Island (outside of the census routes of the Reserve employees) far away from the traditional denning areas of the bears.


The majority of sightings were recorded on the shore-line adjacent to the vast plain areas. .There were many bears that occurred on the spits parallel to the shore. Some individuals were sighted on the gray ice crust in the lagoons between the spits and the shore. Mostly single adult individuals occurred. When the island was flown over, no large groups (more than 6 individuals) were recorded. The physical condition of the animals was characterized as a normal, without considerable deviations towards high fatness or extreme exhaustion.


To estimate the numbers of the bears we developed the following simplest model with assumptions as follows: 1) the island is represented as a circle of 50 km in radius, 2) the activity zone of the bear is within 12 km from the shore, 3) the population density of bears is regular at a fixed distance from center of the Island, increasing from the zero on the inner boundary of the zone of activity to the maximum on the shore, following the cubic law (y~x3, where x is the distance from the internal boundary of the ring ), 4) in a two-kilometer shore zone at the same moment there are 100 individuals. For such a model, the total number of bears on the Island is 187. It should be noted that for the actual estimate of the number this simplified can-not be used and is only adduced as reference for further analysis.


The table represents the zones of a model area whose external boundary coincides with the shoreline and the inner passed at a different distance from the shore and the inner boundary passes at a different distance from the shore (from 500 m to 8 km). For each zone, the area is reflected in relation to the activity zone within 12 km from the shore and absolute and relative number.


Distance from the coast (km)







Number of bears







Relative density of population (%)







Relative area of the habitat (%)








At a distance of 2 km from the shore, 100 individuals were sighted. That value is one of the model‘s parameters. In a three-kilometer zone there are 131 individuals. In case the model is correct and on condition that all the bears recorded in the course of the aerial survey were up to 3 km from the shore, the result is that the observers recorded 88% of the individuals. It that zone is to be expanded to 5 km, one third (31% of the individuals) fail to be recorded. In this case at a width of the shore zone of observation of 3 km, 28% of the activity zone is ob-served, and at a width of the zone of 5 km, 45%. According to the model, 31% of all the bears were at a distance of up to 1 km from the shore; 53%, up to 2 km from the shore; and 70%, up to 3 km. At a distance of over 8 km from the shore there is concurrently a pair of bears, i.e., 1% of the bears at 30% of the area under consideration.


The Island perimeter being 350 km and in case of sighting of 8 individuals from board the ship in the shore area of ±6 km from Ushakovsky and extrapolation of those findings to the entire Island, it can be deduced that on the shore within the light day one can sight 240 individuals. If in the model parameters instead of the cubic density increase towards the shore, a square increase is assumed, the number of bears on the Island will be estimated at 227.


To analyze the ice conditions affecting the numbers of bears on the Wrangel Island, a spatial index of ice cover was estimated, characterizing annually from June 15 to September 15 for each surface feature, the relative number of the days when the ice concentration is over >95% (Fig. 2). Except the water area section situated south of the Wrangel Island, from the other sides it was surrounded by more packed ice than usual. Hence, there are grounds to believe that in the autumn 2010, there could be fewer bears on the Island than in the years with lower ice cover.


The authors are thankful to the Northern Directorate for Hydrometeorological Serice, the crews of the research expedition ship ―Mikhail Somov and the helicopter of the 2nd and the helicopter of the 2nd ОАОА. The aerial survey was performed with permission and with immediate participation of the Director of the Reserve А.R. Gruzdev The study was supported by the Russian Geo-graphical Society.


Solovyev B.A., Platonov N.G., Rozhnov V.V., Mordvintsev I.N.