Evaluation of an Aerial Survey of Pacific Walruses (<i>Odobenus rosmarus divergens</i>)

Estes, James A.; Gilbert, James R.

doi:10.1139/f78-178

Cited by 36 publications

(40 citation statements)

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“…My sources of published records were Chechulin (1936), Belopol'skii (1939), Collins (1940), Freiman (1941), Nikulin (1941Nikulin ( , 1947, Wilke (1942), Porsild (1945), Lantis (1946), Rainey (1947), Brooks (1953Brooks ( , 1954, Fay (1957), Manville (1961), Fedoseev (1962Fedoseev ( , 1966, Yablokov and Bel'kovich (1963), Burns (1965), Anonymous (1965), Harington (1966), Johnson et al (1966), Krylov (1966aKrylov ( , 1968, Gol'tsev (1968), Kosygin and Sobolevskii (1971), Watson and Divoky (1972), Stirling (1974), Tomilin and Kibal'chich (1975), Pinigin and Prianish- nikov (1975), Heptner et al (1976), and Estes and Gilbert (1978). Most of the unpublished data are from aerial surveys conducted by H. W. Braham, J. J.…”

Section: Distribution and Migrationsmentioning

confidence: 99%

“…A large number of animals remains along the northern coast of Chukotka and in the vicinity of Barrow. Other herds are distributed along the fringe of the pack between Barrow and Wrangell Island but are concentrated mainly east of 170 W and west of Herald Island (Estes and Gilbert 1978; J. J. Burns, personal communication).…”

Section: September (Fig 12)mentioning

confidence: 99%

“…Each is unreliable to some degree because of problems encountered in obtaining and interpreting the data on which it was based. Ray and Wartzok (1976), Chapman et al (1977), and Estes and Gilbert (1978) have reviewed most of those problems in detail.…”

Section: Aerial Censusmentioning

confidence: 99%

“…Whereas the American estimates were based on extrapolation from counts along randomly placed strip transects, the Soviet estimates were based on photographic counts of animals on the hauling grounds plus conservative guesses as to the numbers at sea (not sampled). Extrapolation from the American strip transects to the total area occupied could have led to overestimates or underestimates, due to the nonrandom distribution of the animals (Estes and Gilbert 1978). The Soviet counts only of animals on the haulouts probably were low, due to underestimation of the proportion of the population at sea.…”

Section: Aerial Censusmentioning

confidence: 99%

See 3 more Smart Citations

Ecology and Biology of the Pacific Walrus,Odobenus rosmarus divergensIlliger

Fay¹

1982

North American Fauna

387

567

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Section: Distribution and Migrationsmentioning

confidence: 99%

Section: September (Fig 12)mentioning

confidence: 99%

Section: Aerial Censusmentioning

confidence: 99%

Section: Aerial Censusmentioning

confidence: 99%

See 2 more Smart Citations

Ecology and Biology of the Pacific Walrus,Odobenus rosmarus divergensIlliger

Fay¹

1982

North American Fauna

387

567

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“…Visual survey techniques are used widely to estimate abundances of target organisms in terrestrial (Caughley et al 1976, Caughley 1977, Francis 1994) and aquatic (Keast & Harker 1977, Solazzi 1984 environments. In marine research and monitoring, visual survey techniques range from aerial surveys of large mammals (Estes & Gilbert 1978, Leatherwood 1979, Holt & Colongne 1987, Marsh & Sinclair 1989 to counts of fishes and benthos by SCUBA divers (Brock 1954, Bouchon-Navaro 1980, Williams 1982, Wilhams & Hatcher 1983, Eckert 1984, Sale et al 1984, Harmelin-Vivien et al 1985, Ayling & Ayling 1986, 1992, Doherty 1987, McCormick & Choat 1987, Mapstone & Ayling 1993, and even in situ counts of microscopic sessile organisms with underwater microscopes (Kennelly & Underwood 1984).…”

Section: Introductionmentioning

confidence: 99%

Observer effects and training in underwater visual surveys of reef fishes

Aa¹,

Bd²

1997

Mar. Ecol. Prog. Ser.

145

107

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Visual survey techniques are used widely to estimate abundances of target organisms in terrestrial and aquatic environments. There are a number of methodological 'errors' in almost all applications of visual surveys. Given the dependence of all visual survey data on the skill and technique of the observer, one potentially important source of imprecision andlor bias is vanation among and within observers. In studies involving large amounts of fieldwork over great geographic range and many years, it is inevitable that observers will change from place to place and through time at any single site as they are replaced or gwn experience. We present the results of 3 observer tralningkalibration exercises that lnd~cate that observational studies in which multiple observers must be employed may be subject to considerable observer-related biases and imprecision. We found that careful training and calibration of observers ameliorated such effects for most taxa, but non-trivial levels of bias for some taxa and imprecision m estimates for several taxa remained even after thorough training. It is essential that the influence of observer bias and impreclslon be well documented in multi-observer monitoring studies, so that (spurious) patterns related to differences among observers can be distinguished from real spatial or temporal patterns in the environment.

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Pacific Walrus and climate change: observations and predictions

MacCracken

2012

Ecology and Evolution

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The extent and duration of sea-ice habitats used by Pacific walrus (Odobenus rosmarus divergens) are diminishing resulting in altered walrus behavior, mortality, and distribution. I document changes that have occurred over the past several decades and make predictions to the end of the 21st century. Climate models project that sea ice will monotonically decline resulting in more ice-free summers of longer duration. Several stressors that may impact walruses are directly influenced by sea ice. How these stressors materialize were modeled as most likely-case, worst-case, and best-case scenarios for the mid- and late-21st century, resulting in four comprehensive working hypotheses that can help identify and prioritize management and research projects, identify comprehensive mitigation actions, and guide monitoring programs to track future developments and adjust programs as needed. In the short term, the most plausible hypotheses predict a continuing northward shift in walrus distribution, increasing use of coastal haulouts in summer and fall, and a population reduction set by the carrying capacity of the near shore environment and subsistence hunting. Alternatively, under worst-case conditions, the population will decline to a level where the probability of extinction is high. In the long term, walrus may seasonally abandon the Bering and Chukchi Seas for sea-ice refugia to the northwest and northeast, ocean warming and pH decline alter walrus food resources, and subsistence hunting exacerbates a large population decline. However, conditions that reverse current trends in sea ice loss cannot be ruled out. Which hypothesis comes to fruition depends on how the stressors develop and the success of mitigation measures. Best-case scenarios indicate that successful mitigation of unsustainable harvests and terrestrial haulout-related mortalities can be effective. Management and research should focus on monitoring, elucidating effects, and mitigation, while ultimately, reductions in greenhouse gas emissions are needed to reduce sea-ice habitat losses.

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Evaluation of an Aerial Survey of Pacific Walruses (Odobenus rosmarus divergens)

Cited by 36 publications

References 0 publications

Ecology and Biology of the Pacific Walrus,Odobenus rosmarus divergensIlliger

Ecology and Biology of the Pacific Walrus,Odobenus rosmarus divergensIlliger

Observer effects and training in underwater visual surveys of reef fishes

Pacific Walrus and climate change: observations and predictions

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