TOWARDS A TRANSITION FROM SINGLE- SPECIES TO ECOSYSTEM- BASED MANAGEMENT

10.11 TOWARDS A TRANSITION FROM SINGLE- SPECIES TO ECOSYSTEM- BASED MANAGEMENT

The requirement for ecosystem-based manage- ment derives its validity from a stark set of alterna- tives: either the beginning of the 21st century will see a transition towards ecosystem-based man- agement in most areas currently exploited by major fisheries, or it will see the destruction of the ecosystems exploited by these same fisheries. Until recently, the call for ecosystem-based management could be dismissed by regulatory agencies intent on continuing business as usual because ecosystem management tools were not available. The sets of conceptual tools mentioned above, notably Ecopath, Ecosim and Ecospace can, however, be used to identify the key elements of management strategies that would enable fish- eries to be sustained by sustaining the ecosystem in which they are embedded. The two major tools available for this are:

1 Ecoseed: a routine for seeding marine protected areas (MPAs), originally covering only one cell within the spatial grid in an Ecopath/Ecospace map, then identifying, by brute-force computa-

tions, the sequence of cells which, when added to that initial seed, will contribute most to overall benefits, either in terms of market values calcul- ated as species caught multiplied by their price, minus cost of catching them, and/or in terms of their existence values, for example, as whale abun- dance to the whale-watching industry. Results of various Ecoseed runs for different systems show, in accordance with theoretical expectation, that MPAs should be large relative to exploited areas. Important here is that MPAs simulated this way consider all trophic interactions between the species included in an ecosystem model and not only the expected biomass increase of a few charis- matic species.

2 An optimization approach structured around Ecosim’s ability to identify the mix of fleet- specific fishing mortality which optimizes cumu- lative benefits over a set period, e.g. 30 years, under any of the following constraints: (a) maximizing net return to the fishery, which generally involves moderate mortality on valu- able target species and a small overall level of effort; (b) maximizing employment, which means iden- tifying the fleet configuration which sustainably exploits the ecosystem, albeit with an effort level as high as possible. This high effort leads to high employment; (c) maximizing ecosystem maturity, by identify- ing the fleet configuration which maximizes, for all groups in a system, the sum of product of bio- mass and B/P. The latter is in accordance with Odum (1969) who predicts the highest product of

B and B/P for the long-lived organisms typical of mature systems; (d) mandated rebuilding, wherein the fleet config- uration is sought which enables faster rebuilding towards a set threshold as required. This could result from a consequence of a legal decision; (e) optimizing a mix of (a)–(d) wherein any of these can be given different weights.

These two approaches combined and used inde- pendently allow scientists, for any ecosystem for which a suitably detailed Ecopath model has been previously constructed, to explore the implica- tions of various policies, and to quantify their out-

225 comes in economic and social terms, and in the

Ecosystem Models

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