Coleen Moloney of

Marine and Coastal

Management Speaks about Progress in

 

Despite much initial scepticism from critics, a mass balance ecosystem modelling approach is slowly gaining acceptance worldwide. Using software called "Ecopath with Ecosim", many practitioners are developing dynamic ecosystem models for different ecosystems, and a recent (4-8 December 2000) conference in the Galapagos Islands illustrated how some of these models are being used to assist fisheries managers. I attended the conference, entitled "Placing fisheries in their ecosystem context", and report here on some of the main points.

In brief, traditional single species fisheries models make assumptions about natural death rates of fish, and use information from catches to estimate death rates caused by fishing. This can be unsatisfactory, because it is often assumed that other fish populations in the ecosystem (and therefore natural death rates) remain constant. Models such as "Ecopath with Ecosim" are able to estimate deaths from both natural causes and fishing, because they use information about the diets of the species in an ecosystem, and how predator and prey populations change over time. These models can therefore investigate the effects of one fishery on another, because fishing causes changes in the species composition of fish communities.

 

The "Ecopath with Ecosim" software has been developed primarily by three scientists, all currently based at the University of British Columbia: Villy Christensen, Daniel Pauly and Carl Walters. Consequently, many of the applications of the new software are being carried out in Canada, where there is also great interest in ecosystem approaches because of the collapse of the cod fishery in the 1990s.

 

Some of the new software developments have outpaced the capacity of many users to stay abreast, but Lynne Shannon, a scientist at Marine and Coastal Management, has been using and applying the software for a number of years. Ms Shannon, who recently submitted her PhD thesis to the University of Cape Town, was able to build on the results of ecosystem research that has been carried in South Africa for the past two decades. Her PhD thesis represents an in-depth investigation of "Ecopath with Ecosim" models for the Benguela ecosystem, and the ways in which such models could be used to provide insights about fisheries impacts in our marine ecosystems.

 

In future, Ms Shannon will extend this work to use new features of the software. In addition to incorporating time- and space-varying effects, there are also plans to include analyses of social and economic effects of fisheries. At the Galapagos conference, Manuel Zetina-Rejón reported how he used "Ecopath with Ecosim" models to investigate socio-economic factors in some Mexican fisheries. It is hoped that these methods can be adapted and applied here, allowing true integration of social and biological sciences in a South African fisheries context.