Managing adequately the exploitation of commercial species subject to
technical interactions is a key step towards the ecosystem approach to
fisheries. We evaluate here, using a bio-economic modelling approach
building on the ISIS-Fish simulation platform, the relative impact of total
allowable commercial catches (TACC) and of taxes applicable to over-quota
landings (deemed value) on the sustainability of a selection of species
exploited by the New Zealand hoki (Macruronus novaezelandiae) fishery. We investigate some aspects of
the hoki mixed fisheries, consisting of four fleets and nineteen
métiers, by considering the technical interactions between hoki and
Southern hake (Merluccius australis). The dynamics of effort allocation were modelled using gravity model, using value per unit of effort (VPUE) as attractivity
coefficient. Several management scenarios, based on different levels of
TACC, effort limits and deemed value have been defined. The impact of these
strategies on spawning biomass and catches has been investigated. The
results confirm that the deemed value may, in combination with TACC, be an
efficient management tool. By increasing the hoki deemed value, we could
somehow limit the decrease in the hoki TACC needed to harvest Western hoki
sustainably. Constraining hoki fishing also restricts Southern hake fishing
in the Chatham Rise and in the West Coast South Island, but leads to
increased targeting of this species in the Sub-Antarctic area. The relative
costs of renting/buying quota or paying the deemed value are most
constraining when the hoki TACC is at relatively low level and when the hoki
deemed value is more than 1.5 times the current value.