Title: Trophic modelling as a tool to evaluate and manage Iceland´s multispecies fisheries

The main purpose of this project is primarily to attempt, for the first time, to detail a steady-state model of tropic interactions and organic matter transfer in the Icelandic fisheries, using user-friendly software, ECOPATH (version 4 alphas). The rationale behind this is to present to the Icelanders an optional tool for the evaluation and management of multispecies fisheries such as the Icelandic fisheries. Ecopath is user friendly in a number of important features: (i) use of a “generalized linear inverse” matrix routine allowing the system of linear equations used to estimate model parameters to over- or slightly underdetermine; (ii) estimation of (almost) any set of unknowns and not only of biomasses; (iii) explicit consideration of respiratory, ejective and excretory losses (with default provided for inputs) and of the detritus pathways; (iv) estimation of numerous derived quantities on species groups or a whole-system basis, such as gross and net efficiencies, tropic levels, food electivity, pathways and cycles involving any groups and “ascendancy” sensu R. E. Ulanowicz.

The model presented was based mainly on published data and personal communications from staff of Marine Research Institute. It was structured around commercially important fish groups and shrimp with a top predator (i.e. Gadus morhua L.) evaluated at 1.3 t.km-2. Biomass estimates obtained for other fish were considered very reasonable and comparable with estimates from analytical tools used in Iceland. The results of mixed tropic impacts, trophic aggregation, and other network analyses are presented. The input data and results are expressed on area basis and thus cover the total marine fisheries waters of Iceland. The period modeled here is 1997 and 1998.