Bycatch and directed harvest drive high green turtle mortality at Baja California Sur, Mexico

Evaluating mortality of rare marine megafauna is crucial for conservation planning, but logistically difficult to undertake at sea. From 2006 to 2008 we assessed mortality of endangered green turtles (Chelonia mydas) through surveys of beaches and town dumps for stranded and discarded carcasses at nine index sites along the coast of Baja California Sur, Mexico (BCS). We found a total of 778 carcasses, 93% of were immature. Mortality rates ranged from 0.05 to 9.20 carcasses km^-1year^-1 at beaches and 2.84 to 66.75 carcasses year^-1 at dumps. All carcasses found at dumps (N=339) were attributed to human consumption, whereas cause of death at beaches was largely unknown (62%), followed by bycatch (30%), and consumption (8%). Over two thirds of total mortality resulted from consumption (48%) and bycatch (20%), and turtles that died from these causes were significantly larger than those that died from unknown reasons. The majority of carcasses at beaches (69%) and dumps (57%) were found during summer months when small-scale gillnet fisheries operate, including 99% of identified bycatch mortality. Three hotspots accounted for 77% of all mortality, which was disproportionately high (40% of total mortality) at one site where mass-bycatch/stranding events occurred annually. Our results demonstrate that many green turtles are being killed from bycatch and directed harvest at BCS despite over two decades of federal protection; thus, highlighting the need to mitigate these threats at mortality hotspots.