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

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manatees for 21 sampling points per two-week survey period for 6 survey periods per year
and repeated our power analysis as described above.
In the Drowned Cayes, 28 out of 54 point scan locations have a greater than 30%
probability of sighting a manatee (LaCommare et. al, 2008). Would restricting our survey
protocol to locations with a higher sighting probability yield a greater ability to detect a
trend? We generated new negative binomial distribution parameters using our manatee
count data from 2001 - 2007 from locations with a greater than 30% probability of sighting
a manatee (LaCommare et. al 2008). Using these parameters, we generated a new random
array of the number of manatees for 28 sampling points for 6 two-week survey periods.
We repeated our power analysis as described above. From that distribution, we also created
an array of the number of manatees for 8 two-week survey periods with both 28 and 21
points and for 8 two-week survey periods, 28 points with just a 20-minute scan duration.
3. Results
3.1 Index and encounter probability
Histograms of time-to-first sighting indicate that for locations that had a greater than 30%
probability of sighting a manatee, 90% of all manatees are sighted within the first 20
minutes of a 30-minute scan (Figure 2). For locations that had a less than 30% probability
of sighting a manatee, it took slightly longer to spot the first manatee and 90% of all
manatees were sighted within 24 rather than 20 minutes (Figure 2).
The number of manatees sighted per scan was not affected by sighting conditions
(overall Likelihood Ratio Chi-Square = 12.578, df = 18, p = 0.816, n= 131, Table 1). None
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