Pages (PDF 3 MB) - Otter Specialist Group

IUCN Otter Spec. Group Bull. 26(2) 2009
Surveying season
Consideration of season is important in rivers with intermittent water regimes.
As the effect of water level and rain can mask the influence of other variables in otter
sprainting activity, it is important to survey in months that minimize these effects. In
Mediterranean countries that may principally be in the summer and autumn. When
performing single surveys these should not be implemented during the days after
heavy rain or high water level (according to Chanin, 2003, there should be a period of
at least five days without rain before surveying). Also, when dealing with sprainting,
one should take into account seasonal variations in otter sprainting behaviour, which
maybe up to tenfold between seasons (e.g. Kruuk, 2006). So, annual monitoring
schemes should be conducted each year in the same season to diminish otter
sprainting behavioural differences.
Survey length and width
Similarly to river surveys, 600 m transects are a reasonable compromise for
otter regular monitoring, either only to detect otter presence/absence or for more in
depth comparative studies. The survey should be concentrated in the first five metres
from shore of the entire width of the bank flooding area. Nevertheless, for monitoring
otter presence/absence in dams in dry regions, 200m transects are adequate as this
minimises survey time and thus the number of sites to be surveyed per day. However,
this survey length should only be used when more than one site is to be surveyed in
the same reservoir. Alternatively, surveys may be planned to begin with 200m
transects, moving up to a maximum of 600m transects in case no otter signs are
found. Similarly to river surveys, this has the effect of avoiding false negatives.
Number of survey sites
To make it possible to say that otters are present in all of a reservoir, a series of
regularly spaced survey sites, approximately 5 km apart, should be established. This
degree of surveying in depth would give an insight into the otter’s specific habitat use,
such as whether they are present at the point where tributaries run into the reservoir,
or if they use the overall perimeter of the reservoir.
Location of the survey sites
When performing presence/absence surveys, and if proving otter presence in the
entire reservoir is unimportant, the most crucial aspect is choosing the right sites for
surveying. Suitable sites are usually selected by ease of access. Our data suggest that
surveys located in the main inflow of the tributaries into the reservoir (Pedroso,
unpublished data; Sales-Luís et al., 2007) are ideal places to survey. However, it must
be considered that this is not necessarily representative of otter use in the totality of
the reservoir perimeter, particularly when dealing with large reservoirs. To improve
the probability of finding otter signs, surveys should be located on gently sloping
banks, with many suitable potential marking places, near shallow water and beside or
under any existing bridge. The dam wall itself can also be a good place to consider
surveying, providing the wall is not steep and is a short distance from the downstream
river, allowing otters to cross (Figure 4). Furthermore, if surveys are replicated
seasonally, special attention must be given to traditional otter marking places in order
to promote efficiency in detecting spraints.
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