2012 COURSE DATES: AUGUST 4 – 17, 2012 - Sirenian International

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former characterized as estimating relative abundance, the latter absolute abundance (see
Thompson 2004; Williams and Thomas 2009). These authors caution against the use of
indices in favor of more robust estimating procedures such as distance sampling or mark-
recapture procedures (e.g. Anderson 2001; Williams and Thomas 2009). Yet, as long as the
population index is linearly related to actual abundance – that is it doesn’t have an
asymptote or bottom threshold, and detection probabilities are constant over space and
time, count-based indices are valid (Skalski et al. 1983; Thompson 2004; Williams and
Thomas 2009).
Species behavior – long dive times, short surfacing bouts - and severely limited
resources hamper the ability to conduct robust monitoring procedures on Antillean
manatees and other sirenians in developing nations (Aragones et al. in press; Aragones et
al. 1997; Dawson et al. 2008; Dick and Hines 2011). Distance sampling requires the ability
to consistently measure the distance from the observer to the animal using a range finder,
reticulated binoculars or spotting scope (Buckland et al. 2001). Sirenians often surface
very briefly and only expose their nose to the surface when breathing. In our study, even
the best trained observers captured distances via range finder only 10% of the time
(LaCommare and Self-Sullivan, personal observation). Mark-recapture methods are
equally challenging. It is estimated that 50% of manatees in the study area are scarred by
boats (Self-Sullivan 2008). Although possible (Self-Sullivan 2008; Auil and Powell,
personal communication), above-water photo identification methods are difficult because
manatees in Belize and other tropical habitats do not seasonally aggregate at warm water
sites, nor do they tend to float at the surface, exposing their scarred backs. Therefore,
photo-identification via underwater video capturing techniques is more appropriate.
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