Region area estimation

To calculate the area of each region, the extent of likely suitable habitat within them was determined. As nurse sharks do not generally occupy open water [22,39], only the extent of Reef ecosystem (comprising forereef and backreef), and the Lagoon ecosystem (patchreef and seagrass beds) were used for area estimation. The geographic extent of each ecosystem was enumerated from a spatially referenced map of the ecosystems of Belize (2015 version; [39]). Previous BRUV surveys conducted in the country suggest that nurse sharks are absent from lagoon areas further away from reef systems (FG unpublished data). For NBZ and SBZ, the Lagoon ecosystem extended to areas not covered by the surveys but unlikely to host nurse sharks; for these reasons, the Lagoon ecosystem in these areas was restricted to a strip delimited by the reef edge and stretching to a maximum of 2 km landward, although we acknowledge that this arbitrary threshold may be imperfect.