Latest revision as of 14:31, 27 March 2017

Abstract

The present paper elaborates on the status of both harbor and spotted (largha) seal populations on the Komandorsky Islands. Local populations of these seals have doubled since the 1980s. The total population of harbor and spotted seals at both Bering and Medny Islands is now estimated to be 4000–4300 animals. Various methods of counting have been applied. A methodological approach to counting seals on the Komandorsky archipelago is described.

Keywords

Harbor seal ; Spotted seal ; Bering Islands ; Komandorsky archipelago

Introduction

True seals of the Komandorsky Islands are mainly represented by two species: the Kuril subspecies of harbor seal (Phoca vitulina stejnegeri ), and the spotted seal (Phoca largha ). The ribbon seal (Histriophoca fasciata ) and the northern elephant seal (Mirounga angustirostris ) are two other species that sporadically appear swimming into the waters of the islands. Remains of the bearded seal (Erignathus barbatus nauticus ) have been noted on the islands. One exception is the authors' observation of a young individual bearded seal resting for a few days on the reef near the shore of Nikolskaya Bay during the autumn of 2012. Formerly known as Bering ringed seals (Pusa hispida krascheninnikovi ) were relatively frequently observed on the islands ( Barabash-Nikiforov, 1947 ; Marakov, 1967  ;  Marakov, 1972 ). Since the early 1990s, however, there have been no significant observations of these animals. Spotted and harbor seals of Komandorsky Islands are well adapted to the year-round lack of ice cover, reproduce on the foreshore. Until recently, spotted and harbor seals were identified as different subspecies of the common seal Phoca vitulina (P. v. larga ). Only since the mid-1980s have researchers identified the spotted seal as a separate species ( Truhin, 2005  ;  Kuzin, 2010 ). Unlike the spotted seal, which gives birth mainly in April, the Kuril subspecies of the common seal P. v. stejnegeri gives birth from May to June. In addition, the Kuril subspecies develops an adult tipe fur cover in the womb. Adult spotted seals and harbor seals also have different skeletal and tracheal structures ( Kosygin, 1975 ; Czapski, 1975 ; The Red Book of the Russian Federation (Animals), 2001  ;  Kuzin, 2010 ). Although both seals are regularly observed on the islands, their predict differentiation is possible by pups only, because adult animals are very similar (Figs. 1 a, b, 2 ).

Fig. 1. a, b. Color options of insular seal females and pups (July 2008, Komandorsky archipelago, Medny Island, Cape Bobrovye Stolbi). Photo by Zagrebelniy S.V.

Fig. 2. Cub of spotted seal (March 1997, Komandorsky archipelago, Bering Island, near the village of Nikolskoye). Photo by Zagrebelniy S.V.

Countings of seals in the waters of the Komandorsky Islands were made irregularly. Until the early 2000s, complete recordings of island groups of insular and spotted seals had not been conducted. However, non-experts repeatedly attempted to estimate the abundance of animals in permanent haul-outs. George Steller noted the “great crowd” of seals during the wintering period of the Second Kamchatka expedition in 1741–1742 on Bering Island (Steller, 1995 ). Following the arrival of permanent residents (particularly inhabitants of the Aleutian Islands and Alaska), however, the consumption of natural resources increased while the seal population declined sharply. This decline continued until the 1950s (Suvorov, 1912 ; Ilyina, 1950  ;  Marakov, 1967 ). On Medny Island, for example, main haul-outs of “spotted seal” (the term used for all true seals until the mid-1980s) are preserved only in the northern part of the island in its conservation area, which at that time a disappearing sea otter population maintained (Barabash-Nikiforov, 1947 ). According to Marakov (1967) , the reduction in the number of main food resources (e.g., northern fur seals, whose meat was used to feed local people and arctic foxes) in the Komandorsky Islands during the nineteenth century may have led to a change in the local complex of food storage of natives. The population was therefore forced to switch to the true seal (spotted and harbor seals) and the Steller sea lion. The decrease in the population of insular seals during the first quarter of the twentieth century was also fostered by the transition to an intensive exploitation by natives of Arctic fox population (during the “islands fur farming” from 1928 to mid-1955). However, in the late nineteenth century, Grebnitsky (1902) suggested that the disappearance of many haul-outs and rookeries on Bering Island likely demonstrated a change in the general physiographic conditions rather than the extermination of the seals by man, as the haul-outs disappeared across the entire island, not just near the village of Nikolskoye.

Since the early 1950s, the number of animals, at least on Medny Island, began increasing noticeably, and even several new haul-outs appeared. Some researchers (Marakov, 1967 ) attributed the increase in the number of harbor seals to the increasing population of Steller sea lions, as the latter became the primary object of anthropogenic press due to the higher nutritional quality of meat. In the 1950s, the total number of insular seals around Komandorsky Islands was approximately 1500 animals. The literature of that period does not provide an accurate method of population estimation used by Komandorsky fur-farm staff conducted the seal population counts. Nevertheless, from different sources, it has become clear that one-time counts were not completed. Instead, animals were counted mainly from either rookeries during the coastal trip or from the boat at selected sites during sea otter population counts at Medny Islands (Burdin et al ., 1991  ;  Annual reports Komandorsky Fisheries inspection of Sevvostrybvod, 1968–2011 ). Because sea otters did not appear on Bering Island until the late 1970s, marine recordings were not performed. Instead, the number of animals was assessed during observations at main available rookeries in the northern part of the Bering island (during the winter arctic fox hunting period) or during single observations from a boat or on hiking trails during the summer in the southern part of the island. According to a Komandorsky Fisheries inspection (Annual reports Komandorsky Fisheries inspection of Sevvostrybvod, 1968–2011 ), the number of seals on the islands from the late 1960s until 1978 was approximately 1000–1300 individuals. The population then increased to 2400–2700 individuals, 1600–1800 of which were on Bering Island (Annual reports Komandorsky Fisheries inspection of Sevvostrybvod, 1968–2011  ;  Marakov, 1978 ). Comprehensive accounting attempts were begun in the mid-1980s, but these studies were combined with sea otter recordings, and the total number continued to rely on several sources: the winter ground counts from hunters, summer offshore accounts, and random observations of rookeries during coastal trip (Table 1 ). At that time, a redistribution of a Bering Islands group of seals among rookeries along the northern coast was taking place. More specifically, there was a reduction in the number of seals at the rookeries at Vaksel Cape, Bolshoy Rakushechnik Bay and an increase in the number of animals at the adjacent rookeries at the capes of Tonkiy, Prolivnoy and Yushina (Annual reports Komandorsky Fisheries inspection of Sevvostrybvod, 1968–2011  ;  Burdin et al ., 1991 ). These fluctuations in the number and location of seals at rookeries are hardly related to changes in prey base, as the animals feed in the coastal zone (during the mass migration of salmon), are tens or hundreds of kilometers from the shore (personal communication Dr. Burkanov), and animal movements between rookeries are significantly smaller compared to the distance to the remote places of feeding.

a. Data on main haul-outs.

b. Data of full marine counts.

The present paper attempts to fill the gap in the evaluation of number of true seals of Komandorsky archipelago, to conduct a full marine count, to develop a uniform methodology for survey work on Komandorsky Islands and to reference the main places of concentration of seals using GIS-technologies.

Methods

Marine countings of true seals were conducted on Medny Island from 5 to 8 July 2003 and from 8 to 9 July 2005. Counts were conducted on Bering Island from July 25 to 26, 2005. This work was completed by the authors of the present paper with the help of Komandorsky Island Reservate employee E.S. Baldin and Sevvostrybvod employee V.V. Vertyankin.

Surveys were conducted from a rubber motorboat when conditions provided good visibility and no strong waves or swells. Surveys were consistently conducted in synchrony with the daily tide (when the number of animals at rookeries is at maximum) and after massive whelping (when females are the most tied to places of whelping). The locations of the main rookeries that were found, as well as the average fluctuations in the number of animals at these rookeries are marked on the map (Fig. 3 ).

Fig. 3. Distribution of the main rookeries of seals on the Komandorsky Islands in 2005.

Aggregations of less than 25 animals are not marked on the map, but they are approximately uniformly distributed on the reefs along the island coasts. During the surveys, the particular species (insular or spotted seals) was not identified on the reason absence of color differentiation of these species, time constraints (short time of tides, changing weather conditions) and distance of the rookeries from the site of maritime registration works.

Since 2005, we have repeatedly attempted to conduct a complete marine survey of Bering island groups of seals. A complete marine survey, however, has not been feasible due to limitations associated with weather and tidal conditions. Surveys were conducted only in some areas of eastern shore, but these data are not discussed in the present paper. The implemented marine surveys provide a minimum population estimation as these records do not include the animals that were feeding while the observations were in progress.

Results and Discussion

In total, 40–45 relatively stable rookeries on Bering Island (along with islands of Toporkov and Ariy Kamen') and 25–30 haul-outs on Medny Island were recorded. The total number and density of animals on the stretch of coastline for both islands is shown in Table 2 .

The total number of two seal species on Bering Island recorded in 2005 is 2827 animals. On Medny Island, 1555 and 1389 animals were recorded in 2003 and 2005, respectively. These data are approximately two times greater than the estimated total during the mid-1980s.

Over the past few years, no significant changes in the mortality of the Komandorsky Islands of insular seals have been observed. Each year, an average of 10 remains in different conditions, are registered on the coast. Legal seal hunting is not permitted. On the reason absent accessible haul-outs for hunting near the village Nikolskoye we estimate the illegal hunting no more than 10 animals per year. Total number of population of harbor seals on the Komandorsky Islands falls within the range of 4000 to 4300 individuals, further research is needed. A necessary future direction for this research is the completion of surveys during the late summer molting period, when the number of animals at rookeries is at maximum. Similar surveys have been completed successfully around Orkney Islands in the northern UK (Thompson and Harwood, 1990 ), where an evaluation of the effectiveness of various accounting methods was made. These accounting methods included land, sea and aerial countings as well as photographing of groups. Because the study showed that the maximum number of animals at haul-outs was recorded by aerial photography during the molting period, this accounting was considered to be the best. Aerial counting at Komandorsky Islands, however, is hardly possible in the near future, and marine and terrestrial records are limited by weather conditions and the period of whelping. In the late summer period, when animals molt, there are either no daily tides or the tides are very short-term. These conditions do not permit completion of a full accounting during a short period. One solution to this problem may be to combine full summer marine surveys with work only in some part of shore and large rookeries simultaneously from the sea and the coast at different times of the year. This strategy can be paired with daily monitoring of these sites to determine the period of maximum population density. Thus, it will be possible to evaluate the number of animals from different points of observation, while mitigating errors during ground surveys. In any case, further work is needed to identify the basic mechanisms and assess the trends of development of the Komandorsky subpopulations of harbor seal and spotted seal.

References

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