The Hammered Hammerheads: Fisheries Dependent and Independent Analyses of Endangered Hammerheads in the Mesoamerican Reef

Limited data exist on the status and behavior of hammerhead sharks (Sphyrna spp.) outside of developed countries. Recent listing on Appendix II of CITES now requires signatories to develop non-detriment findings for three hammerhead species IUCN listed as Endangered. Using fisheries-independent and -dependent methods, data on hammerheads gathered from 2006-2015 throughout Belize and Guatemala reveal low catch per unit effort using longlines and baited remote underwater video (BRUV) installations and strong susceptibility to fishing mortality using nets. Captures by fishery-independent BRUVs and longlines were dominated by great hammerheads (S. mokarran), whereas fisheries data reveal predominance of scalloped hammerheads (S. lewini). Traditional fishers surveyed about the fishery and status of hammerheads highlighted a preference for the use of nets and for the captures of hammerheads due to the value of their fins. Fishers further perceived declines in abundance and distributional shifts of hammerheads in Belize. Fishery-independent capture data for great hammerheads were complemented by the use tri-axial accelerometry and acoustic tagging that further highlighted intrinsic vulnerability to exploitation based on habitual patterns of behavior and habitat preferences. These compiled data suggest that hammerheads will require both national and regional approaches to management, notably harmonized prohibition of net and longline use.