Modelling fisheries displacement in the North Sea and its ecosystem and economic consequences

Description

Expansion of marine protected areas (MPAs) and offshore windfarms in the North Sea will displace fishing activity from traditional fishing grounds. Alleviating arguments are typically that spillover effects from enhanced production in the newly protected areas will benefit fisheries in the long-term. But the question remains as to a) what will be the whole ecosystem effects of these developments since displaced fishing effort will instead be concentrated elsewhere and b) what will be the costs and benefits to the fishing industry?

Here we describe a big-picture modelling approach to the problem, combining an intermediate complexity end-to-end ecosystem model (StrathE2E, [1]) with a bio-economic model of the spatial dynamics of fishing.

The fishing model assumes a set of métiers – groups of vessels using the same gear and targeting a similar set of species. Revenues for each métier arise from modelled landings. Fixed costs per vessel are assumed constant. Variable costs incurred by each métier scale with time spent fishing, distance from ports to fishing grounds, and density-dependent interference between vessels of the same and different métier. Hence, confining vessels into a smaller area leads to increased interference costs. Then, vessels of each métier are assumed to be seeking to spatially distribute in proportion to their profitability – analogous to the ideal free distribution in ecology - subject to a social adaptability parameter that describes each métiers’ degree of responsiveness to changing circumstances. When all métiers have achieved an ideal-free state this represents a Nash Equilibrium since no métier can independently improve its overall profitability.

The model was calibrated for the period 2003-2013, when international economic data across all métiers are available from the EU STECF, and pre-dating the expansion of MPAs and windfarms. Results from this baseline model were then compared with a scenario model in which the area of each seabed habitat in the model accessible to fishing was reduced on the basis of operational, approved but yet to be constructed, applied-for, and prospective MPAs and windfarms listed by OSPAR in 2021.

Results from the baseline-scenario comparison showed that most seabed-contact métiers were forced further offshore in the ‘beyond 2021’ scenario and suffered unsustainable increases in costs (Break-even Ratio declining to < 1). Despite overall fishing effort remaining constant, the changing spatial distribution of fishing alone had negative effects on the upper trophic level guilds in the ecosystem model due to a combination of indirect trophic and direct by-catch effects.

The motivations and imperatives of MPA and windfarm developments in terms of biodiversity conservation and reducing reliance on fossil fuels are understood. Less well understood are the consequences in terms of whole ecosystem structure and function, and the price to be paid by the fishing industry. Our model suggests that the consequences of these developments may be more far-reaching than anticipated.

Period	6 Dec 2023
Event title	MASTS Annual Science meeting 2023
Event type	Conference
Location	Glasgow, United KingdomShow on map
Degree of Recognition	National