A new method of counting phoca vitulina ssp. Stejnegeri (phocidae, carnivora) on the commander islands (Russia)

Abstract

The Kuril Seal Phoca vitulina ssp. Stejnegeri is a permanent inhabitant of the coast of the Commander Islands. The ecology of the Kuril Seal, and in particular, the features of its life cycle, the population structure and the level of fertility are poorly known. Most publications are devoted to the study of populations and spatial distribution of this animal on the islands. From June to October 2017, the current occurrence, features of spatial distribution, reproductive success of Phoca vitulina ssp. Stejnegeri, seasonal dynamics of the number and the comparison of the accuracy of various methods of its counting have been carried out on Bering Island, Toporkov Island, Ariy Kamen Island, and at a site Bobroviye Kamni on Medniy Island. The material on the number and spatial distribution of the seals was collected using an unmanned aerial vehicle, quadrocopter (drone). In this study, the Kuril Seal was first counted on the islands by aerophotography. The determination of the population size has been carried out during the active reproduction phase of the Kuril Seal-from mid-June to 10th July 2017. Our study showed that the accounted abundance of the Kuril Seal was 1543 individuals, including 343 pups on Bering Island and Toporkov Island. The abundance of Phoca vitulina ssp. Stejnegeri on Medniy Island has been counted using the extrapolation method. It was estimated at 689 individuals. And the total number of this animal on the Commander Islands was 3344 individuals. For the first time, we obtained data on the proportion of pups (22.2%) of the Kuril Seal on the Commander Islands in rookeries during the breeding season and the specific birth rate (17.4%) was calculated. Up to 69.3% of the total number of Kuril Seals is present in large rookeries and only a small portion is presented by small groups or individuals. The proportion of pups born in large rookeries is 72%. We found an increase of the Phoca vitulina ssp. Stejnegeri abundance in the rookeries during the moult period (August). The abundance of individuals continued to grow in some rookeries in September. A comparison of the accuracy of the visual, traditional on the Commander Islands, method of animal counting with data obtained using the aerophotography method showed that in the case of counting from the boat, an observer can register an average of 67.7% of adult individuals and 24% of pups. In case of observation from the first seaside terrace of a shore, the observer can see 39.6% of individuals (adults and pups). And in case of observation from the slopes (height of 17 m and higher) the observer can see up to 62% of individuals (adults and pups). To discuss the long-term dynamics of the number of Kuril Seals on the Commander Islands it is required to conduct a detailed analysis of all available data, as they were collected by using different methods, which are not correctly comparable with the newly obtained results.