Beyond the reef: How risk of predation shapes fish movement over sand

On naturally fragmented coral reefs, the reluctance of small-bodied fishes to cross sand is widely considered a predator-avoidance response, but the extent to which distance from safety and how specific predators mediate off-reef movements is unclear. Here, I use video-generated estimates to assess the degree to which sand acts as a barrier to reef-associated fish movement, and I use novel translocations to test how the presence of standardized models of native and invasive predators over sand affects the homing probability of a Caribbean damselfish, Stegastes partitus. The frequency of fish observed over sand fell non-linearly with distance from the nearest reef, and fish were often observed when < 50 m away (~90 fish per hour, 33 species). However, only the native predator model reduced damselfish homing probability over sand. The invasive lionfish (Pterois sp.) did not affect homing, suggesting damselfish are naïve to the threat of predation posed by lionfish.