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

2011; Wiley; Volume: 15; Issue: 1 Linguagem: Inglês

10.1111/j.1469-1795.2011.00502.x

1469-1795

Trevor A. Branch, James D. Austin, Karina Acevedo‐Whitehouse, Iain J. Gordon, Matthew E. Gompper, Todd E. Katzner, Nathalie Pettorelli,

Marine Bivalve and Aquaculture Studies

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). Multiple critiques have also questioned the Myers & Worm (2003) report that total ecosystem biomass of tunas and billfishes – top ocean predators – has declined by 90% (e.g. Banobi et al., 2011). For instance, an examination of these species using Red List criteria finds that only southern bluefin tuna (Thunnus maccoyii) has declined by more than 50% in three generations, while most tuna and billfish species are fished at or above sustainable levels (Collette et al., 2011). So what explains the trends in the development of commercial fisheries? Profits, not predators: Fisheries tend to develop earlier on species that are high priced, large volume and found in more accessible shallow waters, rather than species that are high in food webs (Sethi, Branch & Watson, 2010). Thus, it is hardly surprising that fisheries managers have long focused on highly profitable species, as these are more subject to heavy fishing pressure. Furthermore, the rather sensational prediction that all fisheries will collapse by 2048 (Worm et al., 2006) has been heavily criticized (see Banobi et al., 2011), yet this forecast has ultimately proved to be a catalyst for consensus since it led to a series of remarkable meetings co-chaired by the protagonists Boris Worm and Ray Hilborn. Their key findings were that most fisheries were below target biomass levels (the biomass producing maximum sustainable yield, BMSY), but that harvest rates had been reduced so that most fisheries were expected to rebuild to sustainable levels (Worm et al., 2009). The current status of fisheries assessed by the United Nations and compilations of stock assessments is that 15–24% of fisheries are lightly fished (well above BMSY), 49–53% are fished at or around BMSY, 15–28% of fisheries are substantially overfished (well below BMSY) and 4–13% are collapsed (FAO, 2010; Branch et al., 2011). This picture is further complicated by different definitions of 'overfished'. Many ecologists consider a fish stock to be overfished when biomass falls below BMSY (58% of assessed fisheries fall in this category, Ricard et al., in press), while fishery management in the US and elsewhere defined 'overfished' as biomass lower than half of BMSY (28% of assessed fisheries fall in this category, Branch et al., 2011). We also know relatively little about the status of fisheries in developing countries which have a shorter history of heavy industrial fishing, but where regulation is less stringent. These fisheries, which are an important source of protein, likely face poorer prospects than fisheries in developed countries subject to more rigorous regulations and enforcement. An important joint realization among marine ecologists, conservation biologists and fishery scientists is that low biomass both leads to more negative effects on ecosystems and to lower profits (Hilborn, 2007; Worm et al., 2009). Therefore, although sustainable catches greater than 80% of the maximum (so-called 'Pretty Good Yield', Hilborn, 2010) can be taken from a broad range of biomass levels both above and below BMSY, the new consensus is that we should strive for higher biomass, above BMSY, and treat BMSY as a hard lower limit (Froese et al., 2011). Australia is leading the way by explicitly aiming for the biomass that maximizes economic yield, which is assumed by default to be 20% above BMSY (DAFF, 2007). What then is the future of wild fisheries? There remain few marine systems untouched by fishing (Swartz et al., 2010). Marine catches have been stable or slightly declining since the mid-1990s (FAO, 2010), while fishing effort has expanded (Anticamara et al., 2011). Untapped fisheries are likely small in terms of both catch and revenue (Sethi et al., 2010). It is therefore improbable that we can increase marine fish catches, and we should focus instead on the stewardship of existing fisheries. With few exceptions, fisheries will recover when fishing is reduced (Myers et al., 1995). The most important step that must be taken is to reduce catches of overfished stocks, particularly in areas like the European Union where most fisheries have been reduced to low biomass levels (Froese et al., 2011). Other steps include eliminating subsidies that encourage continued unprofitable fishing, setting aside marine protected areas to retain some insurance against fishing effects and allocating transferable shares of fishing quotas to increase profitability. In developing countries, community quotas, marine protected areas, marine tenure, rotating closures and co-management between fishers and managers can be successful. In fact, the more of these attributes that are present, the higher the chance of fishery success (Gutiérrez, Hilborn & Defeo, 2011). We stand at a crossroad in fisheries conservation. Some of the direst warnings have proven wrong, yet many fisheries remain overexploited and there is little scope for future expansion of marine fisheries. The clearest needs are to rebuild overexploited fisheries in developed countries, while expanding monitoring efforts and management capacity in developing countries. As scientists involved in animal conservation, we should inform efforts to rebuild fisheries so that the oceans of our future contain profitable fisheries on abundant species while minimizing fishing impacts on marine biodiversity.