Fisheries conservation and management: finding consensus in the midst of competing paradigms

[Extract] The state of the world's fisheries has been a prominent and controversial scientific and social issue over the past 20 years (Banobi, Branch & Hilborn, 2011). Influential research has suggested that we have preferentially 'fished down' top ocean predators before targeting their prey (Pauly et al., 1998) and that, as a consequence, these marine predators have declined by 90% (Myers & Worm, 2003). Even worse, it has been argued that current trends will lead to the global collapse of all fisheries by 2048 (Worm et al., 2006). These paradigms have been challenged by recent findings. The original basis for fishing down marine food webs (Pauly et al., 1998) was based on trophic levels – the average position within food webs, where microscopic algae are at trophic level one, herbivores at trophic level two and predators at trophic level three or higher. Pauly et al. (1998) found a precipitous decline in the average trophic level of commercial catches. However, recent analyses of catches and unbiased data from scientific surveys and stock assessments show that mean trophic levels are increasing rather than decreasing, and that this indicator does not reliably track changes in marine ecosystem health (Branch et al., 2010). In any case, in most ecosystems where average trophic level has declined, such trends are due not to waning top-predator catches ('fishing down'), but to increasing catches of low-trophic-level species, or 'fishing through' (Essington, Beaudreau & Wiedenmann, 2006). Where collapses have occurred, they are up to twice as frequent in small, short-lived species low on the food web than in long-lived predators (Pinsky et al., 2011)