Techniques for surveying exploited species - Conservation and Sustainable Use - page 74

this involves attaching tags that give a radio signal, which is then located by
triangulation with a hand-held or vehicle-mounted receiver. However, wildlife
telemetry is being revolutionised by technological advances, with options now
available for automated location recording and data recovery based on global
positioning systems (GPS), the Argos satellite system, cell phone networks, and
static hydrophone tracking of acoustic tags in the marine environment.
Alternatively, animals can be marked with tags that can be identified when they are
either recaptured, recovered dead, or observed in the field. Leg rings on birds
(either metal or coloured plastic to enable reading in the field) are the classic example
of this kind of marking, but technology has again expanded the range of species
and situations to which marks can be applied, for example, subcutaneous passive
internal transponder (PIT) tags, visible implant fluorescent (VIF) tags, coded wire
(CW) tags, and visible implant elastomer (VIE) tags can all be applied to smaller
species that may otherwise be difficult to mark. Section 2.7 provides published and
web resources on all these forms of tracking. While telemetry clearly gives a much
better chance of relocating marked animals, visible tags are cheaper, and many
more of them can usually be fitted. In some cases, visible tags may thus increase
the chances of picking up relatively infrequent, but ecologically significant, long-
distance movements.
Movement rates based on periodic observations at two or more locations are
best analysed by using multi-strata mark-recapture models , which separates the
probability of movement from the probabilities of survival and detection (Lebreton
et al . 2003). Box 2.18 gives an example of this method in action. Alternatively,
combined live-dead analysis can give an indication of the rate of emigration from
the area in which live sightings are recorded if the dead recoveries come from outside
this area (Frederiksen and Bregnballe 2000).
Box 2.18 Migration analysis in action: quantifying Canada goose
movements.
The Atlantic Canada goose Branta canadensis population has a wide distribution
in winter, spanning much of east coast USA (Figure 2.16). While the population
as a whole fared well over the second half of the 20th century, different sections of
this population showed strikingly different patterns of change, with the more
southerly part of the range showing a sustained decline. Hestbeck et al . (1991)
analysed the movements and survival of the wintering population along the east
coast of the USA in order to determine whether the changes in sub-populations
were due primarily to differences in survival rates (potentially linked to harvest
rates), or simply to a redistribution of the population.
The data used come from almost 29,000 geese fitted with coded neck collars
over three years between 1983 and 1986, and over 100,000 re-sightings of
these geese were made up until 1988, assigning all records to one of three