Spatio-temporal interactions between Northeast Atlantic Mackerel and its fishery - Simulating different futures

The mackerel (Scomber scombrus) stock is one of the commercially most important pelagic species in the Northeast Atlantic, being targeted by various nations. Environmental and stock size changes caused a stock expansion after 2007, initiating a yet unresolved dispute between the European Union, United Kingdom, Iceland, Greenland and the Faroe Islands. We analyze the impacts of different Total Allowable Catches (TACs) on the mackerel stock and possible adaptations in simulated fleet behavior by applying an age-structured bio-economic optimization and simulation model, FishRent. We implement dynamic seasonal migration patterns, which alter the spatial extension of mackerel depending on biomass levels, assuming density dependent mechanisms. If true, this is an important consideration because it may provide the possibility for major fishing parties (the European Union, Norway and the UK) to exclude minor parties (Iceland) from fishing mackerel by selecting a high enough fishing pressure and therefore keeping the stock from migrating further north. This can, for instance, be achieved by setting a corresponding TAC. When applying a TAC under a business-as-usual scenario or higher, the stock biomass decreased close to B_MSY on the long-term. In this case, the Danish fleets would benefit, increasing their profit up to 80%. All other fleets were negatively affected with a profit decreasing between 50% and 100% depending on the scenario. When applying a TAC according to the stock advice, the stock biomass was estimated to increase on the long-term. This benefitted the Irish and British fleets, but effects on the Icelandic fleet were neutral.