  Fishing activities have broad impacts that affect, although not exclusively,
the targeted stocks. These impacts affect predators and prey of the harvested
species, as well as the whole ecosystem it inhabits. Ecosystem models can be
used to study the interactions that occur within a system, including those
between different organisms and those between fisheries and targeted species.
Trophic web models like Ecopath with Ecosim (EwE) can handle fishing fleets as
a top predator, with top-down impact on harvested organisms. The aim of this
study was to better understand the Icelandic marine ecosystem and the
interactions within. This was done by constructing an EwE model of Icelandic
waters. The model was run from 1984 to 2013 and was fitted to time series of
biomass estimates, landings data and mean annual temperature. The final model
was chosen by selecting the model with the lowest Akaike information criterion.
A skill assessment was performed using the Pearson's correlation coefficient,
the coefficient of determination, the modelling efficiency and the reliability
index to evaluate the model performance. The model performed satisfactorily
when simulating previously estimated biomass and known landings. Most of the
groups with time series were estimated to have top-down control over their
prey. These are harvested species with direct and/or indirect links to lower
trophic levels and future fishing policies should take this into account. This
model could be used as a tool to investigate how such policies could impact the
marine ecosystem in Icelandic waters.
