Essay Conservation of Marine Megafauna through Minimization of Fisheries Bycatch RAM ¯ UNAS ˇ ZYDELIS, ∗ †† BRYAN P. WALLACE, ∗ † ERIC L. GILMAN,‡ AND TIMOTHY B. WERNER§ ∗ Center for Marine Conservation, Nicholas School of the Environment, Duke University Marine Laboratory, 135 Duke Marine Lab Road, Beaufort, NC 28516, U.S.A. †Center for Applied Biodiversity Science, Conservation International, Arlington, VA 22202, U.S.A. ‡IUCN Global Marine Programme and University of Exeter Centre for Ecology and Conservation, 2718 Napuaa Place, Honolulu, HI 96822, U.S.A. §New England Aquarium, Central Wharf, Boston, MA 02110 and Biology Department, Boston University, 5 Cummington Street, Boston, MA 02215, U.S.A. Abstract: Many populations of marine megafauna, including seabirds, sea turtles, marine mammals, and elasmobranchs, have declined in recent decades due largely to anthropogenic mortality. To successfully con- serve these long-lived animals, efforts must be prioritized according to feasibility and the degree to which they address threats with the highest relative impacts on population dynamics. Recently, Wilcox and Donlan (2007, Frontiers in Ecology and the Environment) and Donlan and Wilcox (2008, Biological Invasions) proposed a conservation strategy of “compensatory mitigation” in which fishing industries offset bycatch of seabirds and sea turtles by funding eradication of invasive mammalian predators from the terrestrial reproductive sites of these marine animals. Although this is a creative and conceptually compelling approach, we find it flawed as a conservation tool because it has narrow applicability among marine megafauna, it does not address the most pervasive threats to marine megafauna, and it is logistically and financially infeasible. Invasive predator eradication does not adequately offset the most pressing threat to most marine megafauna populations—fisheries bycatch. For seabird populations, fisheries bycatch and invasive predators infrequently are overlapping threats. Invasive predators have limited population-level impacts on sea turtles and marine mammals and no impacts on elasmobranchs, all of which are threatened by bycatch. Implementing compen- satory mitigation in marine fisheries is unrealistic due to inadequate monitoring, control, and surveillance in the majority of fleets. Therefore, offsetting fisheries bycatch with eradication of invasive predators would be less likely to reverse population declines than reducing bycatch. We recommend that efforts to mitigate bycatch in marine capture fisheries should address multiple threats to sensitive bycatch species groups, but these ef- forts should first institute proven bycatch avoidance and reduction methods before considering compensatory mitigation. Keywords: compensatory mitigation, elasmobranchs, fisheries bycatch, invasive predators, marine conserva- tion, marine mammals, sea turtles, seabirds Conservaci´ on de la Megafauna Marina Medianate la Minimizaci´ on de la Captura Incidental de Pesquer´ ıas Resumen: Muchas poblaciones de megafauna marina, incluyendo aves, mam´ ıferos y elasmobranquios, han declinado en d´ecadas recientes principalmente debido a mortalidad antropog´enica. Para conservar exitosamente a estos animales longevos, los esfuerzos se deben priorizar de acuerdo con la factibilidad y el grado en que atienden las amenazas con los impactos relativos m´ as altos sobre la din´ amica de la poblaci´ on. Recientemente, Wilcox y Donlan (2007) y Donlan y Wilcox (2008) propusieron una estrategia de conservaci´ on de “mitigaci´ on compensatoria” en la que las industrias pesqueras compensan la captura incidental de aves y tortugas marinas mediante el financiamiento de la erradicaci´ on de mam´ ıferos depredadores invasores ††email zydelis@duke.edu Paper submitted February 22, 2008; revised manuscript accepted September 30, 2008. 608 Conservation Biology, Volume 23, No. 3, 608–616 C 2009 Society for Conservation Biology DOI: 10.1111/j.1523-1739.2009.01172.x