Techniques for surveying exploited species - Conservation and Sustainable Use - page 80

0 50

kilometres

N

Predicted distribution
of green peafowl
(mean number / count)
>2
1.5-2

Dak Lak
Province

1-1.5
0.5-1
>0-0.5
0

Vietnam

Fig. 2.17 Based on call surveys across Dak Lak Province, Vietnam, green
peafowl are most abundant in the northwest of the province, especially near
rivers away from human settlement. Darker shades on the map represent greater
relative abundance, assuming that call frequency correlates well with abundance.
Source: Brickle (2002). Photo: © Nguyen Tran Vy.

2.6 Surveying as a component of monitoring

This chapter shows how it is possible to gather detailed information on many aspects
of a population's demography, but you of course also need to consider practical issues .
Surveying wild species is generally costly, in terms of both time and money, and some-
times personal risk as well. For example, mark-recapture methods usually require very
substantial effort to get good results, perhaps requiring a lot of manpower to deploy
large numbers of costly traps over sufficiently large spatial scales, and there are often
risks of injury or disease in handling animals, both to the handler and the handled.
Direct observation methods such as distance sampling can be more efficient, but not
always—costly equipment may be needed (such as laser range finders for measuring
distances), and scarce or inconspicuous species will require huge distances to be cov-
ered to yield enough data for a meaningful assessment. Weighing up these practicali-
ties requires a good understanding of the field methods that are applicable
to your focal species. Sutherland (1996) provides a useful overview of the survey
methods that are commonly applied to different groups of plant and animal, and there
are many other inventive methods out there—use web and literature searches to find
out what other people have done with species similar to yours.
The costs of surveying need to be weighed against the potential benefits . Some
of the sustainability assessment methods in Chapter 4 require no direct biological
information, and this approach may be adequate if you are explicitly not interested
in the biological component of sustainability. Otherwise, at least some biological
information will be required, usually abundance as a minimum in order to give
a picture of the current state of the population (Chapter 4). A more detailed
understanding of the processes that lead to change in population size can be gained