Compensatory mitigation as a solution to fisheries bycatch–biodiversity conservation conflicts

© The Ecological Society of America www.frontiersinecology.org G fisheries provide approximately 16% of all protein consumed by humans, employ about 200 million people, and are valued at US$82 billion (Botsford et al. 1997; FAO Fisheries Department 2004). Eight percent, or 7.2 million tons, of the global catch is comprised of non-target species and discarded, and this mortality is having major impacts on species and ecosystems (Botsford et al. 1997; Spotila et al. 2000; Baker et al. 2002; FAO Fisheries Department 2004; Lewison et al. 2004). The social and economic importance of fisheries and the biological realities of overfishing and bycatch result in cardinal tensions over ocean resources. Encouragingly, fishing gear modifications and other low-cost measures are effective in reducing bycatch for some species and are currently being implemented (Gilman et al. 2005). However, in other cases, avoiding unacceptable levels of mortality has proven difficult, and costly regulatory interventions are becoming commonplace. New Zealand’s squid (US$122 million per year in revenue in 2006) and Hawaii’s pelagic longline fishery (US$50 million per year in revenue in 2000) have both been recently closed due to bycatch of endangered marine vertebrate species (Ito and Machado 2001; Lane 2005; Martin 2005; Anonymous 2006a, 2007) . Many species that are impacted by fisheries bycatch, such as seabirds and sea turtles, spend part of their lives on land. Events in these terrestrial habitats also often lead to high levels of mortality. For instance, while fishery bycatch is affecting seabirds globally, particularly albatrosses, petrels, and shearwaters (Brothers et al. 1999), this threat pales in comparison with the impact of invasive mammals on breeding colonies (Figure 1). Invasive predators such as feral cats (Felis catus) and rats (Rattus spp) have decimated seabird breeding colonies worldwide, preying on eggs, chicks, and adults of many species (Atkinson 1985; Nogales et al. 2004). Threequarters of seabirds listed by the IUCN are threatened by invasive species, compared with 49% threatened directly or indirectly by fisheries (Figure 2a). Indeed, invasive mammals are responsible for most vertebrate extinctions over the past 6 centuries, and the overwhelming majority of these extinctions have occurred on islands (Groombridge 1992; MacPhee and Flemming 1999). CONCEPTS AND QUESTIONS