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4 - Marking techniques
- Edited by R. M. Laws, St Edmund's College, Cambridge
-
- Book:
- Antarctic Seals
- Published online:
- 05 February 2010
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- 07 October 1993, pp 89-118
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Summary
Introduction
In studies of population ecology or behaviour it is essential to be able to mark individuals in such a way that they can be positively identified when they are re-observed. For certain purposes, however, it is sufficient to identify year classes or a specific group of seals. Even then, if it can be done, individual marking should be attempted because it has the potential of giving so much more information.
The techniques adopted will depend upon the objectives of the research. Long-term marking by brands, tags or intra-vitam staining is necessary for validating age criteria by means of known-age animals; for stock identification; for studies of population dynamics and longevity; for dispersal and migration studies; and for assessing breeding success (e.g. the frequency of pupping). Also in behavioural studies, temporary conspicuous marks can often be used individually or in combination with a routine tagging programme.
The more permanent marking methods usually require a measure of restraint of the animal. This usually presents no problem where pups are concerned, and even adults of some species can be tagged without first restraining them. Usually, however, adults must be immobilized, particularly if reliable weights and measurements are to be taken, if a tooth is to be extracted for age determination, or if the marking procedure is complex. Methods of immobilization and capture are described in chapter 3. The bagging technique devised by Stirling (1966) is adequate for several of the ice-breeding seals with or without partial drugging to slow them down.
2 - Estimation of population sizes
- Edited by R. M. Laws, St Edmund's College, Cambridge
-
- 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.
3 - Immobilization and capture
- Edited by R. M. Laws, St Edmund's College, Cambridge
-
- Book:
- Antarctic Seals
- Published online:
- 05 February 2010
- Print publication:
- 07 October 1993, pp 46-88
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Summary
Introduction
Studies of wild animals often require the capture and immobilization of representative specimens for such purposes as making accurate body measurements, determination of sex and age, collecting of blood or milk samples, or attaching recorders and transmitters. Although great progress has been made in the development of techniques for the capture and immobilization of terrestrial animals using drugs, their use on seals is still in the experimental stage and further work is needed before definitive recommendations can be made for most species.
The use of drugs for the field anaesthetizing of wild animals is considerably more difficult than working with animals in the laboratory or in normal animal practice where information usually exists on the history of the subjects and where greater support facilities and expertise are normally available. Characteristically, the field researcher is faced with the problem of having to immobilize free-ranging animals in difficult situations and often under adverse conditions. The researcher is further required to estimate the body size and physiological state of the animal to be immobilized in order to approximate dosage rates, and not infrequently must proceed without knowledge of the physiological effect of the various drugs on a particular species.
Investigators should also be aware that the distribution or availability of some immobilizing drugs may be restricted so that they are not generally available. Sufficient lead time should be allowed to obtain such things as permits. (See Appendix 16.7.)