Need for a clear and fair evaluation of biodiversity offsets for fisheries bycatch.

Žydelis et al. (2009 [this issue]) is a direct critique of 2 recent papers we published on the use of biodiversity offsets in managing fisheries bycatch (Wilcox & Donlan 2007; Donlan & Wilcox 2008). The authors misrepresent the use of biodiversity offsets as we presented them, misunderstand the policy objectives of fisheries (and bycatch) management, present a flawed analysis of the appropriateness of offsets for seabirds and other marine megafauna, underestimate the cost of standard bycatch reduction measures, and overestimate the data requirements involved in implementing offsets. Žydelis et al. set up a false dichotomy between bycatchmitigation measures and offsets, misquoting us in the process. They state, “we address the case of bycatch offsets as proposed by D&W, where measures for avoidance and minimization of adverse impacts are not required before considering offsets,” which implies the adoption of offsets as a tool forces managers to leave direct mitigation approaches behind. We have consistently eschewed this approach, insisting that offsets should be used only after direct mitigation measures have been implemented. In the abstract of one of our papers that Žydelis et al. cite we state, “A bycatch management framework based on the hierarchy of ‘avoid, minimize, and offset’ from the Convention on Biological Diversity would result in costeffective conservation gains” (Donlan & Wilcox 2008). In our initial paper, we presented a comparison of whether offsets or a fisheries closure would be more cost-effective in reducing the threat to a declining shearwater. This analysis was in the context of direct mitigation measures that were both legally mandated and ineffective in achieving the required degree of bycatch reduction (Wilcox & Donlan 2007). The false dichotomy set up by Žydelis et al. distracts from the real challenges and opportunities of integrating biodiversity offsets into bycatch management. Bycatch is not a problem of species conservation; rather, it is a problem in environmental management