Northeastern Coast Of Sakhalin Island Research Articles

Reproduction, biometric patterns of pink salmon and effect of commercial fishery on the runs of the species on the south of the north-eastern coast of Sakhalin Island in 2021

Purpose: to present up-to-date data on the dynamics of the spawning run, reproduction conditions and biometric characteristics of pink salmon in three reference watercourses in the southern part of the north-eastern coast of Sakhalin Island, as well as analysis of impact of commercial fishing on the spawning run and distribution of spawners within spawning grounds. Methods: common methods of ichthyological research were applied to collect and process field data. Data were synthesized in MS Excel, analysis and visualization were carried out in MS Excel and Statistica. Scientific novelty: results of monitoring of pink salmon in the southern part of the north-eastern coast of Sakhalin are presented. Despite the intensive commercial fishery in this area, there are no other data on the dynamics of pink salmon runs, density of breeders on spawning grounds, and biometric characteristics of spawners, except for those presented in this paper. Result: data on the timing of spawning migration, distribution of pink salmon within spawning grounds and degree of occupation of spawning grounds, temporal structure of spawning run; bio-metric characteristics of pink salmon are presented. Assessment of the influence of commercial fishing on the dynamics of spawning run and distribution of pink salmon within spawning grounds is discussed. Practical relevance: the presented data is an integral part of information supply of fishery research of the most widespread species of Pacific salmon - pink salmon, which forms the basis of salmon fishery in the Sakhalin Region. Also, the presented data is applicable for preparation of scientifically-based recommendations for optimizing the fishing pressure.

The Frequency of Occurrence of the North Pacific Minke Whale Balaenoptera acutorostrata scammoni Deméré, 1986 off the Northeastern Coast of Sakhalin Island in 2008-2021

The Frequency of Occurrence of the North Pacific Minke Whale Balaenoptera acutorostrata scammoni Deméré, 1986 off the Northeastern Coast of Sakhalin Island in 2008-2021

Frequency of Occurrence of the North Pacific Minke Whale <i>Balaenoptera acutorostrata scammoni</i> Deméré, 1986 off the North-Eastern Coast of Sakhalin Island in 2008–2021

The seasonal and interannual variability in the frequency of occurrence of the North Pacific common minke whale (Minke whale) Balaenoptera acutorostrata scammoni Deméré, 1986 off the north-eastern coast of Sakhalin Island (the Sea of Okhotsk) in 2008–2021 was studied. It has been shown that the occurrence of whales of this species in the study area has significant seasonal and interannual variability. The average frequency of occurrence in even years of observations was 1.6 times higher than in odd years and amounted to 7.1 and 4.4%, respectively. It has been suggested that the frequency of occurrence of minke whale in the study area is determined by the intensity of coastal wind upwelling off the eastern coast of Sakhalin Island.

Spatial distribution of pacific herring <i>Clupea pallasii</i> on the northeastern shelf of Sakhalin Island in the modern period

Spatial distribution of pacific herring Clupea pallasii in the Okhotsk Sea waters at the northeastern coast of Sakhalin Island is described on the data of surveys conducted in June-October of 1989 and 1997-2020 using bottom and midwater trawls and Danish seine. The herring distribute widely, with the main aggregations in the area with depth up to 100 m between the Lunsky Bay and Piltun Bay. These aggregations are formed by the native herring of the North-East Sakhalin population, whereas the herring in the deeper waters belong to the Okhotsk population.

A note on the spatial distribution of western gray whales (Eschrichtius robustus) off Sakhalin Island, Russia in 1998

Three aerial surveys were conducted along a portion of the northeastern coast of Sakhalin Island, Russia between August and September 1998. They were conducted to examine the spatial distribution of western gray whales on their feeding grounds, and in relation to current and planned industrial activity. A total of 32 gray whale groups, consisting of 38 whales, was sighted during the surveys. Group sizes ranged from 1-3 individuals (mean = 1.2, SD = 0.54), with 87.5% (n = 28) composed of single whales. All groups detected were within 5km of the shore and 93.8% (n = 30) were sighted inside 4km. Sighting locations ranged from 0.6-4.8km offshore, with an overall mean distance from shore of 2.5km (SD = 1.11). These data suggest that western gray whales feed primarily in waters less than 20m deep and relatively close to shore. The nutrient-rich effluent from a large coastal lagoon is believed to significantly enrich the near-shore benthic environment of the northeastern Sakhalin Island coast, creating an area of particularly high food availability, and in turn contributing to the near-shore affinity of gray whales observed during this study.

Observations of western gray whales by ship-based whalers in the 19th century

Animals belonging to the small, endangered population of western gray whales (Echrichtius robustus) are observed today primarily during the summer open-water season in feeding areas off the northeastern coast of Sakhalin Island, Russia. The migration route(s) and wintering area(s) used by this population are largely unknown. Gray whales once had a fairly extensive distribution in the Sea of Okhotsk but little detailed information has been published on when and where they occurred. Open-boat, ship-based whalers from the United States and a few other countries conducted an intensive hunt for bowhead whales (Balaena mysticetus) and North Pacific right whales (Eubalaena japonica) in the Sea of Okhotsk from the 1840s to 1870s. According to entries in voyage logbooks, the American whalers regularly encountered (and sometimes hunted) gray whales in the far northeastern corner of the Okhotsk Sea (Shelikhov Bay, Gizhiginskaya Bay and Penzhinskaya Gulf) between early May-late August. They also observed gray whales in summer along the northern coast of the sea (especially Tauskaya Bay), around the Shantar Islands, in Sakhalin Bay, off Cape Elizabeth at the northern tip of Sakhalin Island and along the west coast of the Kamchatka peninsula. No evidence was found in the logbooks studied of gray whales (and indeed of whaling effort) off northeastern Sakhalin Island where most observations of gray whales occur in the present day.

Benthic studies adjacent to Sakhalin Island, Russia, 2015 I: benthic biomass and community structure in the nearshore gray whale feeding area

Okhotsk or western gray whales feed in summer along the northeastern coast of Sakhalin Island, Russia, a region with oil and gas extraction facilities. Seismic surveys increased sound levels in the nearshore feeding area in 2015 for part of the summer, potentially displacing whales from preferred foraging habitat or reducing foraging efficiency. Since lost foraging opportunities might lead to vital rate effects on this endangered species, detailed benthic surveys were conducted to characterize benthic community biomass patterns and spatial and temporal differences. Benthic biomass demonstrated strong spatial–temporal interactions indicating that prey biomass differences among locations were dependent on sampling period. Of greatest interest, Amphipoda biomass declined from June to October in the northern and southern portions of the nearshore study area but increased in the middle and Actinopterygii biomass increased in the northern area in mid-summer. Water depth and sediment type were significant covariates with community structure, and water depth strongly covaried with bivalve biomass. Total average prey biomass was ~ 100 g/m2 within the nearshore feeding area with no evidence of reduced biomass among sampling periods or locations, although there were fewer amphipods in the south. Multi-prey investigations provide a stronger basis for inferences than single-prey studies of amphipods when gray whales feed on diverse prey. Benthic community-level variability was moderate to high as would be expected for a shallow-water nearshore area. Overall, spatial and temporal changes in dominant macrofauna biomass reflected small to medium-sized effects that were well within the natural boundaries expected for benthic communities.

Benthic studies adjacent to Sakhalin Island, Russia, 2015 II: energy content of the zoobenthos in western gray whale feeding grounds

The waters adjacent to the northeastern coast of Sakhalin Island, Russia, are an important feeding ground for the endangered western gray whale. Data on the energy available to foraging whales from their prey resources is required for researchers interested in modeling the bioenergetics of whale foraging, but little energy content information is available for the benthic prey communities of gray whales in this region. In this study, we describe the energy density (ED), biomass, and total energy availability (ED × biomass) of benthic prey sampled from two gray whale foraging areas adjacent to Sakhalin Island: the nearshore and offshore feeding areas. ED varied almost seven-fold among benthic taxa, ranging from 1.11 to 7.62 kJ/g wet mass. Although there was considerable variation within most prey groups, amphipods had the highest mean ED of all of groups examined (5.58 ± 1.44 kJ/g wet mass). Small sample sizes precluded us from detecting any seasonal or spatial differences in mean ED within or among taxa; however, mean biomass in the offshore feeding area was, in some cases, an order of magnitude higher than mean estimates in the nearshore feeding area, resulting in higher mean total energy available to foraging gray whales offshore (958–3313 kJ/m2) compared to nearshore (223–495 kJ/m2). While the proportion of total energy accounted for by amphipods was variable, this prey group generally made up a higher proportion of the total energy available in the benthos of the offshore feeding area than in the benthos of the nearshore feeding area. Data presented here will be used to inform bioenergetics modeling of the vital rates of mature females in an effort to improve understanding of population growth limits for western gray whales.

Extended-Reach Drilling Hits Mainstream To Squeeze Difficult Reservoirs

Though expensive and complex, extended-reach drilling (ERD) is moving more into the mainstream as the industry is driven to develop frontier reserves in fragile environments like the Arctic where drilling from shore to off-shore targets reduces a project’s infrastructure costs and environmental footprint. A form of directional drilling, ERD is also being used increasingly to tap into hard-to-produce reservoirs, making viable projects that might otherwise be written off as noncommercial. This article highlights how the Russian Far East became the ERD epicenter in the past decade, given ExxonMobil and Rosneft’s extensive use of ERD in developing Arctic resources offshore Sakhalin Island, and how ERD is becoming more widely used in regions as diverse as the Gulf of Thailand, off-shore Brazil, and the Arab Gulf. By definition, an extended-reach well (ERW) is one in which the ratio of the measured depth (MD) vs. the true vertical depth (TVD) is at least 2:1 (PetroWiki). An ERW differs from a horizontal well in that the ERW is a high-angle directional well drilled to intersect a target point, a feat requiring specialized planning to execute well construction. ExxonMobil subsidiary Exxon Neftegas Limited (ENL), which operates the Sakhalin-1 license area offshore Russia’s Sakhalin Island (Fig. 1), has been pushing the limits of ERD for nearly 2 decades with innovative technologies and sophisticated well planning, making the Sea of Okhotsk a place where any ERD drilling record set today may easily be broken tomorrow. Russia’s state-owned Rosneft (which has a 20% stake in Sakhalin-1) owns bragging rights for having drilled the longest ERW well on record to date. Rosneft announced in November 2017 it had drilled a 15000-m horizontal ERW from the offshore Orlan gravity-base platform at Chayvo field situated in 14 m water depth in the Sea of Okhotsk, topping four previous records set between 2013 and 2015 that had reached between 12450 m and 13500 m (Fig. 2). In a news release at the time, Rosneft called the well “super complex with a DDI [directional drilling index] of 8.0 and a 14129-m stepout.” The release went on to say that the Sakhalin-1 Consortium could (as of the 2017 announcement) claim to have drilled nine out of the world’s 10 longest ERD wells. According to Rosneft, the project had set five world records for measured depth of wells between 2013 and 2017. In April 2015, development well O-14 was drilled with a length of 13500 m. That broke a 2014 record when the 13000-m Z-40 well was completed. In 2013, records were announced for wells Z-43 and Z-42 which were drilled, respectively, in April and in June 2013 with lengths of 12450 m and 12700 m. Rosneft credited ExxonMobil’s patented “Fast Drill” drilling optimization process that can increase rates of penetration (ROP) by up to 400% as a significant innovation contributing to the ERD success story at Sakhalin-1. One of the largest foreign direct investments in Russia, Sakhalin-1 operates under a production sharing agreement (PSA) with its license area off the northeastern coast of Sakhalin Island, comprising the Chayvo, Odoptu, and Arkutun Dagi fields.

Site-fidelity and spatial movements of western North Pacific gray whales on their summer range off Sakhalin, Russia.

The Western North-Pacific (WNP) gray whale feeding grounds are off the northeastern coast of Sakhalin Island, Russia and is comprised of a nearshore and offshore component that can be distinguished by both depth and location. Spatial movements of gray whales within their foraging grounds were examined based on 13 years of opportunistic vessel and shore-based photo-identification surveys. Site fidelity was assessed by examining annual return and resighting rates. Lagged Identification Rates (LIR) analyses were conducted to estimate the residency and transitional movement patterns within the two components of their feeding grounds. In total 243 individuals were identified from 2002–2014, among these were 94 calves. The annual return rate over the period 2002–2014 was 72%, excluding 35 calves only seen one year. Approximately 20% of the individuals identified from 2002–2010 were seen every year after their initial sighting (including eight individuals that returned for 13 consecutive years). The majority (239) of the WNP whales were observed in the nearshore area while only half (122) were found in the deeper offshore area. Within a foraging season, there was a significantly higher probability of gray whales moving from the nearshore to the offshore area. No mother-calf pairs, calves or yearlings were observed in the offshore area, which was increasingly used by mature animals. The annual return rates, and population growth rates that are primarily a result of calf production with little evidence of immigration, suggest that this population is demographically self-contained and that both the nearshore and offshore Sakhalin feeding grounds are critically important areas for their summer annual foraging activities. The nearshore habitat is also important for mother-calf pairs, younger individuals, and recently weaned calves. Nearshore feeding could also be energetically less costly compared to foraging in the deeper offshore habitat and provide more protection from predators, such as killer whales.

Мониторинг естественных нефтепроявлений вдоль северо-восточного побережья острова Сахалин на основе радиолокационных и оптических данных ДЗЗ

Мониторинг естественных нефтепроявлений вдоль северо-восточного побережья острова Сахалин на основе радиолокационных и оптических данных ДЗЗ

Reproductive conditions of walleye pollock Theragra chalcogramma (Gadidae) off the northeastern coast of Sakhalin Island, Sea of Okhotsk

The spatial distribution of eggs and larvae of the walleye pollock Theragra chalcogramma is considered in respect to dynamics of oceanologic processes, nutrients, chlorophyll а and zooplankton off the northeastern coast of Sakhalin Island in spring 2012. It is shown that the effect of severe temperature regime in the near-bottom horizons in the western Sea of Okhotsk during the spawning period of walleye pollock becomes milder due to specific features of water dynamics. The egg distribution is determined by mesoscale eddies in the region. The species survival depends on the effect of such environmental factors as freshwater discharge from the Amur River, eddy structure in waters of the Sea of Okhotsk, and dynamics of phytoplankton and zooplankton development.

Behavioural responses of western gray whales to a 4-D seismic survey off northeastern Sakhalin Island, Russia

A seismic survey was conducted off the northeastern coast of Sakhalin Island, Russia in 2010. The survey area was adjacent to the only known near-shore feeding ground of the Critically Endangered population of western gray whales Eschrichtius robustus in the western Pacific south of the Aleutian Islands. This study examined the effectiveness of efforts to minimize the behavioural responses of the whales to vessel proximity and sound during the survey. Two shore-based behavioural observation teams monitored whale movements and respirations pre-, during and post-seismic survey. Theodolite tracking and focal-animal follow methods were used to collect behavioural data. Mixed linear models were used to examine deviations from 'normal' patterns in 10 movement and 7 respiration response variables in relation to vessel proximity, vessel/ whale relative orientations and 8 received sound metrics to examine if seismic survey sound and/or vessel activity influenced the whales' behaviour. Behavioural state and water depth were the best 'natural' predictors of whale movements and respiration. After considering natural variation, none of the response variables were significantly associated with seismic survey or vessel sounds. A whale's distance from shore and its orientation relative to the closest vessel were found to be significantly influenced by vessel proximity, which suggested some non-sound related disturbance. The lack of evidence that the whales responded to seismic survey sound and vessel traffic by changing either their movement or respiration patterns could indicate that the current mitigation strategy is effective. However, power analyses suggest that our sample sizes were too small to detect subtle to moderate changes in gray whale behaviour.

The current state of populations of the common tern Sterna hirundo (Linnaeus, 1758) and the Kamchatka tern S. camtschatica (Pallas, 1811) in northern Sakhalin

This paper presents data on the numbers of nesting common and Kamchatka tern populations on the northeastern coast of Sakhalin Island over a more than 20-year period. Distribution maps of the main tern colonies (Chaika, Lyarvo, and Wrangel islands, and an unnamed island situated in Chaivo Bay) are given. Taking into account the current data concerning southern Sakhalin colonies, the total number of terns in Sakhalin Island is about 9000 pairs for the Kamchatka tern and up to 16000 pairs for the common tern. The main biotic and abiotic factors that determine the population dynamics and distribution of nesting terns in northern Sakhalin Island are enumerated.

The species composition and quantitative distribution of the diatom genus Pseudo-nitzschia H. Peragallo, 1990 in Russian waters of the Sea of Japan and the Sea of Okhotsk

This paper studies the species composition and quantitative distribution of diatoms that belong to the genus Pseudo-nitzschia in the Russian waters of the Sea of Japan and the Sea of Okhotsk. In total, 11 species of this genus were found in the area, including 7 that are known as being potentially toxic. The highest concentrations of Pseudo-nitzschia microalgae (1.4 × 106–2.7 × 106 cells/L) were found in the summer and autumn in the Peter the Great Bay of the Sea of Japan and the lowest concentrations (2.5 × 102–1 × 104 cells/L) were found in the Sakhalinsky and Akademiya bays of the Sea of Okhotsk. The species diversity of potentially toxic diatoms was greatest (seven species) and the cell concentrations highest (over 6 × 105 cells/L) in the Peter the Great Bay, Sea of Japan, and in the Aniva Bay, Sea of Okhotsk. The density of potentially toxic species was highest near the northeastern coast of Sakhalin Island, in the Amur River estuary, and in adjacent waters. This paper also presents geographical distribution maps of Pseudo-nitzschia species and maps of the density distribution of potentially toxic microalgae over the studied area and identifies potential amnesic shellfish poisoning areas.

Leaner leviathans: body condition variation in a critically endangered whale population

The role of environmental limitation and density-dependent regulation in shaping populations is debated in ecology. Populations at low densities may offer an unobstructed view of basic environmental and physiological interactions that impact individual fitness and thus population productivity. The energy reserves of an organism are reflected in its body condition, a measure linking individual fitness and the environment. From 1997 to 2007, we monitored the critically endangered western gray whale (Eschrichtius robustus) population on its primary summer feeding ground off the northeastern coast of Sakhalin Island, Russia. This effort resulted in a large data set of photo-identification images from 5,007 sightings of 168 individual whales that we used to visually assess western gray whale body condition. We quantified temporal variation in the resulting 1,539 monthly body condition determinations with respect to observations of reproductive status and sex. Western gray whale body condition varied annually, and we identified years of significantly better (2004) and worse (1999, 2006, and 2007) body condition. This study is the 1st to track the within-season body condition of individual whales. Body condition improved significantly as the summer progressed, although results suggest that not all whales replenish their energy stores by the end of the season. The body condition of lactating females was significantly worse than that of other whales at all times and was most often determined to be compromised. The body condition of their weaning calves exhibited no temporal variation and was consistently good. It is possible lactating females provide an energetic buffer to their offspring at the expense of their own body condition and future reproductive success. Findings from the analysis establish a foundation for quantifying links between western gray whale body condition, demographic parameters, and environmental conditions; and provide a baseline for monitoring individual and population condition of an ecosystem sentinel species in a changing environment. Overall, this study highlights the presence of density-independent environmental and physiological mechanisms that affect the abundance and growth of populations.

The growth and life span of bivalve mollusks at the northeastern coast of Sakhalin Island

Numerous shells of bivalves, which study attributed to 37 species, were collected from samples of ground taken with a Van Veen dredge sampler at the northeast coast of Sakhalin Island at depths of about 10–60 m in June–October 2003–2009. Tellina lutea, Mactromeris polynyma, Serripes groenlandicus, Macoma spp., Liocyma fluctuosum, and Siliqua alta occurred most often in the samples. The assessment of growth in 18 bivalve species revealed common patterns of age variations that were irrespective of their way of life, maximum body size, and maximum age. The greatest annual increment in shell length was observed in the first 4 years of life, and the asymptotic size of the mollusks was reached with a 10-fold decrease in the annual growth rate. The life span of the mollusks varied from 2 up to 41 years and sometimes significantly differed from that of the studied species in other areas of their range, clearly displaying the ecological conditionality of this parameter. Species with maximum ages of less than 10 years were the most numerous in the bivalve community of the region. The results of the research are discussed in relation to the nature of the environment at the northeast coast of Sakhalin Island.

The peculiarities of foraging migrations of the Korean-Okhotsk gray whale (Eschrichtius robustus) population in russian waters of the Far Eastern seas

Photographic identification of the Korean-Okhotsk gray whale Eschrichtius robustus population has been conducted since 2002 by researchers of the Institute of Marine Biology at the Far East Branch of the Russian Academy of Sciences (IMB FEB RAS), with financial support provided by Exon Neftegas, Ltd. and Sakhalin Energy Investment Co., in order to study the migration features and biology of this species. In 2008, photo-ID studies were carried out in two areas, off the northeastern coast of Sakhalin Island and off the southeastern coast of Kamchatka. As a result of the studies, 122 whales known from the Sakhalin gray whale catalogue were photographed. Of them, 97 individuals were registered off Sakhalin, 24, off Kamchatka, and one whale was observed at both sites. In addition, 25 more gray whales that had not been sighted off Sakhalin Island before were found off the coast of Kamchatka. Based on these photographic materials, the whales physical and skin conditions were also analyzed. Cases of sightings of gray whales in areas that are remote from their traditional summer and fall feeding grounds in the Far Eastern seas of Russia are discussed.

Population abundance and growth rate of western gray whales Eschrichtius robustus

ESR Endangered Species Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials ESR 6:1-14 (2008) - DOI: https://doi.org/10.3354/esr00106 Population abundance and growth rate of western gray whales Eschrichtius robustus Amanda L. Bradford1,*, David W. Weller2, Paul R. Wade3, Alexander M. Burdin4,5,6, Robert L. Brownell Jr.7 1School of Aquatic and Fishery Sciences, University of Washington, Box 355020, Seattle, Washington 98195-5020, USA 2Southwest Fisheries Science Center, NMFS, NOAA, 8604 La Jolla Shores Drive, La Jolla, California 92037-0271, USA 3National Marine Mammal Laboratory, Alaska Fisheries Science Center, NMFS, NOAA, 7600 Sand Point Way NE, Seattle, Washington 98115-6349, USA 4Kamchatka Branch of Pacific Institute of Geography, Far East Branch of the Russian Academy of Sciences, Pr. Rybakov, 19-a, Petropavlovsk-Kamchtsky 683024, Russia 5Alaska SeaLife Center, 301 Railway Avenue, Seward, Alaska 99664, USA 6University of Alaska Fairbanks, PO Box 757500, Fairbanks, Alaska 99775, USA 7Southwest Fisheries Science Center, NMFS, NOAA, 1352 Lighthouse Avenue, Pacific Grove, California 93950, USA *Email: alb992@u.washington.edu ABSTRACT: The western population of gray whales Eschrichtius robustus is one of the most endangered whale populations in the world. Recent studies of this population off the northeastern coast of Sakhalin Island, Russia, have produced a photographic dataset that was utilized for the first mark-recapture assessment of western gray whale abundance. Given encounter histories of 129 individually identified whales spanning 25 monthly capture occasions from 1997 to 2003, a closed capture estimator was employed to estimate the number of individuals using the study area in each year. Temporary emigration probabilities were then applied to the closed capture estimates to enumerate the total population size of whales off northeastern Sakhalin Island. Total abundances from 1997 to 2003 were estimated as 64 ± 5.1 (SE), 55 to 75 (95% CI); 75 ± 4.9, 66 to 85; 86 ± 3.1, 80 to 93; 77 ± 4.7, 68 to 87; 91 ± 3.4, 84 to 98; 98 ± 4.1, 90 to 106; and 99 ± 4.9, 90 to 109, respectively. These abundance estimates, particularly the last values in the series, most likely approximate the size of the entire western gray whale population. For comparison to the trend in the abundance estimates, life history data were used to estimate the growth rate of the population. Depending on the range of potential fecundity values incorporated, the resulting growth rate estimates indicate an annual population increase that is between 2.5 and 3.2%. The extremely small population size and slow rate of increase documented here further highlight concern about the viability of this critically endangered population. KEY WORDS: Abundance · Mark-recapture · Temporary emigration · Population growth rate · Simulation approach · Photo-identification · Western gray whale · Sakhalin Island, Russia Full text in pdf format NextCite this article as: Bradford AL, Weller DW, Wade PR, Burdin AM, Brownell RL Jr. (2008) Population abundance and growth rate of western gray whales Eschrichtius robustus. Endang Species Res 6:1-14. https://doi.org/10.3354/esr00106 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in ESR Vol. 6, No. 1. Online publication date: September 09, 2008 Print ISSN: 1863-5407; Online ISSN: 1613-4796 Copyright © 2008 Inter-Research.

Population abundance and growth rate of western gray whales Eschrichtius robustus

The western population of gray whales Eschrichtius robustus is one of the most endan- gered whale populations in the world. Recent studies of this population off the northeastern coast of Sakhalin Island, Russia, have produced a photographic dataset that was utilized for the first mark- recapture assessment of western gray whale abundance. Given encounter histories of 129 individu- ally identified whales spanning 25 monthly capture occasions from 1997 to 2003, a closed capture estimator was employed to estimate the number of individuals using the study area in each year. Temporary emigration probabilities were then applied to the closed capture estimates to enumerate the total population size of whales off northeastern Sakhalin Island. Total abundances from 1997 to 2003 were estimated as 64 ± 5.1 (SE), 55 to 75 (95% CI); 75 ± 4.9, 66 to 85; 86 ± 3.1, 80 to 93; 77 ± 4.7, 68 to 87; 91 ± 3.4, 84 to 98; 98 ± 4.1, 90 to 106; and 99 ± 4.9, 90 to 109, respectively. These abundance estimates, particularly the last values in the series, most likely approximate the size of the entire west- ern gray whale population. For comparison to the trend in the abundance estimates, life history data were used to estimate the growth rate of the population. Depending on the range of potential fecundity values incorporated, the resulting growth rate estimates indicate an annual population increase that is between 2.5 and 3.2%. The extremely small population size and slow rate of increase documented here further highlight concern about the viability of this critically endangered population.