Table 1.

ECI	In-water visibility	Maximum depth (m) ± SE	Detection zone (m)
1	clear water, bottom clearly visible	All depths1	All depths1
2	variable clarity, bottom visible but not clearly	2.07 ± 0.50	0 to 2.0
3	clear water, bottom not visible	3.45 ± 0.59	0 to 3.5
4	turbid water, bottom not visible	1.59 ± 0.70	0 to 1.5

Means and standard errors (SE) of the maximum depths at which Dugong Secchi Disks were visible to experienced aerial observers under the Environmental Conditions Index (ECI), plus the depths of the detection zones used to estimate the proportion of time dugongs were available to aerial observers.

¹ The experiment was not repeated for ECI1 because by definition all dugong models were available for detection by trained observers in aircraft at 500 ft (~152.4 m) under such environmental conditions.