Increasing mortality of Endangered Antillean manatees Trichechus manatus manatus due to watercraft collisions in Belize

Abstract

Belize maintains the largest proportion of the Endangered Antillean manatee Trichechus manatus manatus population in its range, but tourism and boat traffic have increased substantially over the past 3 decades. We utilized 25 yr of Belize Antillean manatee stranding data (1995-2019), 6 aerial surveys (1997, 1999, 2000, 2001, 2002, 2014), and 2 decades of boat registration data to examine: (1) spatial patterns in stranding incidence and risk of watercraft collision; (2) temporal patterns in strandings and registered watercraft; and (3) the relationship between manatee strandings attributed to watercraft collision and watercraft numbers. The number of watercraft collision strandings increased significantly over time, from 1-4 yr-1 in the late 1990s and early 2000s to 10-17 yr-1 in the late 2010s. The per manatee risk of watercraft collision stranding increased across space and time with the number of registered boats. Strandings were greater in areas of high boat traffic, high human population density, and mangrove habitats, particularly in Belize City and Placencia. These results highlight the need to reduce the threat of watercraft collisions to conserve this Endangered subspecies in Belize. Conservation efforts should focus on reducing the number of boats and their speed within zones of high manatee use to reduce mortality due to boat collisions, including establishing additional non-motorized vessel areas, restricted access, and reduced speed zones.