Trade‐offs between objectives for ecosystem management of fisheries

Abstract

The strategic objectives for fisheries, which are enshrined in international conventions, are to maintain or restore stocks to produce maximum sustainable yield (MSY) and to implement the ecosystem approach, requiring that interactions between species be taken into account and conservation constraints be respected. While the yield and conservation aims are, to some extent, compatible when a fishery for a single species is considered, species interactions entail that MSY for a species depends on the species with which it interacts, and the yield and conservation objectives therefore conflict when an ecosystem approach to fisheries management is required. We applied a conceptual size- and trait-based model to clarify and resolve these issues by determining the fishing pattern that maximizes the total yield of an entire fish community in terms of catch biomass or economic rent under acceptable conservation constraints. Our results indicate that the eradication of large, predatory fish species results in a potential maximum catch at least twice as high as if conservation constraints are imposed. However, such a large catch could only be achieved at a cost of forgone rent; maximum rent extracts less than half of the potential maximum catch mass. When a conservation constraint is applied, catch can be maximized at negligible cost in forgone rent, compared with maximizing rent. Maximization of rent is the objective that comes closest to respecting conservation concerns.

Maximizing fisheries yields while maintaining community structure

“…If regulations are needed, it would therefore be better to control access than to regulate the fishing pattern. Fisheries management is always a balance of trade-offs (Link 2010;Andersen et al 2014), and for many fisheries, particularly in the Northern Hemisphere, the value of the catch is strongly correlated with the size of the fish, in which case, size restrictions combined with low effort may be appropriate. In the developing world, however, food production, in particular healthy food containing essential micronutrients, is still of major importance (Food and Agriculture Organization of the United Nations (FAO) 2014; High Level Panel of Experts on Food Security and Nutrition (HLPE) 2014), and in such situations, a fishing pattern such as the Zambian side of Lake Kariba seems to be optimal from ecological, sociopolitical, and nutritional aspects (Kolding et al 2015a), the latter because small fish are usually sundried and eaten whole, in contrast to large fish, which are filleted or smoked, thereby losing many essential micronutrients (Longley et al 2014) in addition to being more expensive to process.…”

Unplanned ecological engineering

“…Accounting for costs by maximizing profit instead of revenue would lead to lower exploitation rates. Doing so could, at least partially, accommodate conservation of biodiversity (3). Further, the impoverishment of the ecosystem will have economic consequences beyond the fishing industry (e.g., in recreational fisheries or tourism).…”

“…The theoretical support for such a feat of ecosystem engineering is well developed (2,3). Trusting the Chinese catch statistics, Szuwalski et al…”

High fishery catches through trophic cascades in China

“…For example, high-yield agriculture occurs in simplified food chains, rather than in wild pastures or forests (6). Diverse models of marine ecosystems have predicted that obtaining maximum total yield involves removing predators from the system (3,7), and this phenomenon has been observed widely in freshwater environments (8). Reported marine cases are fewer but also exist.…”