Aerial surveys were carried out in 2009 and 2010.

Comprehensive studies on the beluga whale abundance and distribution of the northern and south-western parts of Okhotsk Sea were conducted only three times in 1980-s. Most of published papers provide only direct visual count estimates without any math analysis. The absence of standardized method makes comparison of the data between years difficult if not impossible. During almost 20 years, until 2009, aerial surveys of the Okhotsk Sea beluga whales have not been conducted; the abundance of whales is unknown. Here we present a summary of the results of 2009 and 2010 aerial surveys and provide the beluga whale abundance estimates for each of the survey regions of the Okhotsk Sea.

Aerial surveys with the modern technical equipment were conducted in late summer from a specially equipped airplane AN-38 using the same method in 2009 and 2010. Almost all the Okhotsk Sea coastal waters were covered. In 2009, before conducting the main abundance survey, we flew a series of reconnaissance flights in the western part of the sea (Shantar region) and covered the entire water-area of the bays using the parallel track-line method. We found belugas only in coastal zones, which proved economical ineffectiveness of such method in the given region. In future, parallel or chain-saw track-line survey was conducted only in Sakhalinsky Bay and the Amur Estuary. In other regions, the survey was conducted as a continuous coastal flight (direct count) that allowed detection of all beluga coastal aggregations. Each year, we surveyed the western part of the sea twice: in 2009, the first series of flights was conducted on August 5-8, and the second one – on September 11-13; in 2010 both surveys were conducted in August with a 15-day interval (August 7-8 and 23-24). The other regions were surveyed once each year. Flight altitude on-effort was predominantly 400 m, but could range from 300 to 700 m.

Beluga abundance estimate was calculated based on visual observations corrected and supplemented – especially for dense aggregations – with the photo-material analysis. Due to the large size of the water-area surveyed, we divided it onto the survey regions that corresponded to geographic features of the coastal water-area. Abundance estimate was conducted separately for each survey region. For the southern part of Sakhalinsky Bay and the Amur Estuary, beluga abundance was calculated in the program ―BELUKHA 2 with the extrapolation method. For the other regions where we conducted direct count, beluga abundance was taken to be equal to the number of animals detected by the observers, and in cases of large aggregations – visually observed number corrected with photographs. All estimations did not take into account belugas invisible to observers due to being underwater (no availability correction); thus, we consider the obtained results as ―minimal abundance. As a result of our flights, we found out that in August-September belugas mainly concentrate in the mouths of big rivers. The major beluga aggregations (over 100 individuals) that we detected may be grouped according to two regions spatially set apart: northeastern part of the Okhotsk Sea (Gizhiginskaya, Penzhinskaya gulfs and the coastal waters of western Kamchatka) and western part of the Sea (The Amur Estuary, Sakhalinsky Bay, the bays: Baikal, Nikolaya, Ulbansky, Tugursky, and Udskaya Gulf).

In the north-eastern part of the Okhotsk Sea, between August 21 – September 7, 2009, we detected 1027 beluga whales. In addition, a group of 15 whales was recorded for Tauyskaya Gulf. Penzhinskaya Gulf was surveyed under poor conditions (low fog), there for we suspect an underestimate for this survey region in 2009. In 2010 (August 13-19), we found 1333 belugas in the north-eastern part of the Sea; in Tauyskaya Gulf no belugas were sighted. The coastal waters of Penzhinskaya Gulf were surveyed under the good weather conditions, and the number of observed belugas doubled that from the previous year. We consider the results for 2010-survey are more demonstrative for this part of the Sea, and suggest that the 2010 beluga abundance estimate be used for this region. During the first beluga count in the western part of the Okhotsk Sea (survey 2009-1), 1853 belugas were observed. During the second survey, 1567 belugas were detected. As show our data, relatively few belugas were detected in Sakhalinsky Bay in survey 2009-1. This fact has lead to a low estimated abundance, which can be explained by ineffective (reconnaissance) route design that mainly covered the open part of the bay not typically used by belugas in summer. A significant difference (August vs. September flights) in numbers of whales observed in the Shantar region bays may have been caused by the worse weather conditions in September or/and by the fact that the flights were conducted at different tide phases.

In 2010-1 survey we visually detected 4470 whales. During the second series of flights we did not have a chance to survey Udskaya Gulf, the place for the largest in the Shantar region aggregation of belugas. Therefore, the data from 2010-2 survey may not be used for the abundance estimate in the western part of the Sea. In the rest of the survey regions of this part of the sea we found 2220 belugas. We consider survey 2010-1 be the most representative and comprehensive for the western Okhotsk Sea, and suggest the data obtained during August 7-8 flights are used for the total Okhotsk Sea beluga abundance estimate

Thus, our estimate of minimal beluga abundance in the Okhotsk Sea, based on the data from the surveys of a satisfying quality, equals 6116 (СV=6.8%) whales.

1. A.N. Severtsov Institute of Ecology and Evolution RAS, Moscow, Russia

2. Scientific Research Institute "Giprorybflot", St. Petersburg, Russia

3. ―Dolphin and I‖, Ltd., Moscow, Russia

4. Geographical faculty of M.V. Lomonosov Moscow State University, Moscow, Russia

Glazov D.M.1, Chernook V. (I.2), Shpak O.V. (1,3), Solovyev B.A. (1,4), Nazarenko E.A. (1), Vasilev A.N. (2), Chelintsev N.G. (1), Kuznetsova D.M. (1), Mukhametov L.M. (1,3), Rozhnov V.V. (1).