Ecopath model

Model Name:	Australia, Great Barrier Reef
Year:	2005
Remarks:	By its charter the Great Barrier Reef Marine Park Authority (GBRMPA), must balance the needs of indigenous traditional owners, commercial and recreational fishing interests, and the conservation requirements of the Great Barrier Reef (GBR) marine parks World Heritage Area status. Under both Commonwealth and State legislation, as well as through international obligations of the World Heritage Area listing, management of the marine park is committed to the ecologically sustainable development of fisheries, and most importantly, conservation of their supporting ecosystems. In the current study the basic Gribble (2000) "GBR prawn" ECOPATH trophic model was expanded into a "linkedecosystems" model, which considered the biodiversity and connecting biomass flows within and between (1) mangrove, (2) lagoon-seagrass, and (3) coral reef systems of the GBR. The GBR linked-ecosystem model is an equilibrium trophic hierarchy, with the biomass flows balanced such that there are not more predators than prey to feed them, nor conversely are there "wasted" prey with insufficient predators to exploit the available resource. Thirty-two trophic guilds were modelled, including 25 from original "GBR prawn" model (Gribble, 2003), plus inshore finfish species groupings and juvenile life-history stages. This spectrum represents a generalised food-web that attempts to capture the major biomass dynamics the and flows within the component GBR systems. The model was implemented by means of ECOPATH EwE (version 5 beta) software using the ECOSIM and ECOSPACE routines for temporal and spatial simulations respectively. The particular application for the model was to identify the effects of the major fisheries in each of the component systems, and the possible confounding effects of independently developed fisheries management plans. Accordingly, long-term temporal simulations of the GBR linked ecosystem model explored the interactions across the line, gillnet and trawl fisheries, and highlighted a number of issues. In both the Sea turtle and Barramundi trophic guilds there were significant interactions between fisheries that are important to the management of these stocks. It appears that there is not a simple intuitive link between fishing pressure and biomass of some targeted species, but a more complex "food-web" effect. Targeting of fish or prawn aggregations by commercial fishers reduces the efficacy of logbook catchper- unit-effort (CPUE) as an index of abundance or biomass because the reported catch rate reflects only the densities of fish or prawns within the aggregation or school, not the unbiased estimate of abundance obtained if the population was randomly sampled. Therefore it would be expected that the biomass trajectory predicted by the ecosystem model and by the logbook data would show a reasonably poor match, as was evident in this study. This result has implications for the reliability of traditional single-species surplus-production stock assessment models that use CPUE to model the maximum sustainable yield of a fishery.
Model span:	0, to 0,
# Groups:	25
Pedigree:	No input
Location:	, ; ,
Reference:	Gribble, N. A. (2005) CD Ecosystem modeling of the Great Barrier Reef: A balanced trophic biomass approach. In Zerger, A. and Argent, R.M. (eds) MODSIM 2005 International Congress on Modelling and Simulation. Modelling and Simulation Society of Australia and New Zealand, December 2005, pp. 170-176. ISBN: 0-9758400-2-9. http://www.mssanz.org.au/modsim05/papers/ascough_1.pdf
Contact:	Neil A Gribble
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