3 results
A top–down, multidisciplinary study of the structure and function of the pack-ice ecosystem in the eastern Ross Sea, Antarctica
- S.F. Ackley, J.L. Bengtson, P. Boveng, M. Castellini, K.L. Daly, S. Jacobs, G.L. Kooyman, J. Laake, L. Quetin, R. Ross, D.B. Siniff, B.S. Stewart, I. Stirling, J. Torres, P.K. Yochem
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- Journal:
- Polar Record / Volume 39 / Issue 3 / July 2003
- Published online by Cambridge University Press:
- 26 June 2003, pp. 219-230
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We used a top–down, multidisciplinary approach to examine the physical and biological environment of the pack ice of the eastern Ross Sea (approximately 125–170°W) during the austral summer of 1999/2000 from RVIB Nathaniel B. Palmer and its ship-based helicopters. The approach focused on pack-ice seals while incorporating studies of biotic and abiotic factors that may influence the distribution and abundances of these apex predators in the Ross Sea to yield a holistic understanding of the structure and function of this complex, large marine ecosystem. This research represented the US component of the international Antarctic Pack Ice Seal (APIS) program, which was designed to document the circumpolar distribution and abundance of Antarctic pack-ice seals. The eastern Ross Sea is one of the two major areas in the Southern Ocean where substantial pack ice exists throughout summer. We found that vast multi-year ice floes (>20 km diameter) and smaller floes north of the shore-fast ice front provide a unique habitat for seals and penguins (apex predators) to forage and haul out while molting in late summer. Farther north, more Ross seals were observed than in any previous surveys in the circumpolar pack ice, perhaps because they are attracted to the area in summer to molt on large stable first-year ice floes. Extensive fast ice along the coastline and drifting pack ice in the shelf–slope boundary zone provided haul-out areas for seals and penguins with access to feeding in the coastal shelf region. Distributions of potential prey for seals and penguins varied over the study area, as determined by nets, acoustics, and diving surveys. Antarctic krill (Euphausia superba) were found throughout the survey region, overlapping the distributions of two smaller species, Thysanoëssa macrura (primarily off-shelf) and E. crystallorophias (primarily found on-shelf). In some locations, E. superba occurred at high densities underneath ice floes, where they foraged on the sea-ice microbial community. Two general fish communities, oceanic and shelf, were distinguished. Off-shelf fishes were members of the classic oceanic midwater fish fauna, whereas on-shelf fishes were Antarctic endemics. The abundance of pelagic fishes was relatively low throughout the study area compared with other Southern Ocean ecosystems. In contrast, benthic fish biomass and diversity on-shelf were high (41 species, 6 families). Hydroacoustic analyses indicated that densities of potential prey were highest in the coastal shelf region where large aggregations of euphausiids (primarily E. crystallorophias) and individual juvenile Antarctic silverfish (Pleuragramma antarcticum) occurred.
Preface
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- By D.B. Siniff
- Edited by R. M. Laws, St Edmund's College, Cambridge
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- Book:
- Antarctic Seals
- Published online:
- 05 February 2010
- Print publication:
- 07 October 1993, pp xi-xii
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Summary
The need for a handbook to standardize techniques for studying Antarctic seals was recognized during the initial meetings of the SCAR Group of Specialists on Seals. Even during various discussions between experts about the results from various national Antarctic programmes, it became clear that a lack of standardization sometimes made it difficult to make direct comparisons between studies. For example, even apparently small variations, such as the use of different types of tags placed in flippers for long-term identification of individuals had the potential to cause differences in estimates of population parameters. The problems of lack of standardization in data collection were even more critical when less experienced persons were involved. In remote areas such as the Antarctic where the number of personnel on a base or a ship may be limited, scientific and non-scientific staff with no training in pinniped research are sometimes required to record various types of observations on seals. Similarly, from time to time, non-experts may have unique opportunities to record very important observations on seals. Without a standardized format that could be readily available to everyone; it was clear that valuable opportunities and data would be lost and the full scientific value of some studies might not be realised. Consequently, the SCAR Group of Specialists on Seals undertook to produce a handbook of standardized techniques for the study of Antarctic seals, the benefits of which would also carry over to the study of Arctic seals and facilitate more bi-polar comparisons.
Completion of this volume has taken longer than was originally envisaged.
2 - Estimation of population sizes
- Edited by R. M. Laws, St Edmund's College, Cambridge
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- Book:
- Antarctic Seals
- Published online:
- 05 February 2010
- Print publication:
- 07 October 1993, pp 29-45
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Summary
Introduction
This chapter provides a review of the methods which are currently available for estimating the size of Antarctic seal populations. Such estimates have a wide range of potential uses, ranging from the evaluation of the status of a species as part of a management or conservation plan, to the use of the species' abundance as an indicator of prey availability. However, there is no one estimation technique which is suitable for all purposes. The choice of a suitable technique will depend on the use which will be made of the results, the logistic constraints imposed on the survey team, and the basic biology of the species involved. The following sections have been designed to provide sufficient information about the available techniques to allow a choice between them to be made. They provide some advice on the general direction for subsequent analysis of results, but calculations of the precision and accuracy of the resulting estimates must be left to individual investigators. However, these latter calculations are essential to any estimate of abundance and anyone contemplating making such estimates should ensure that they will have access to adequate statistical advice during the design of a survey and the subsequent analysis of results.
Basic considerations
First it must be recognized that it is practically impossible to make a total census of all the age-classes in any seal population. Seals partition their time among areas such as beneath the surface of the sea, hauled out on land or ice, or at sea; the time spent in these habitats varies depending on sex, age and season.