Potential consequences of implementing the EU Landing Obligation on marine ecosystems can be listed in two categories:
Food shortage: Reduction in the discard flow may lead to a food shortage for some scavenger species including birds, benthic and demersal fish and invertebrates.
Altered exploitation: New constraints for fishing fleets are expected to translate into changes in the exploitation (reduced fishing mortality, changes in the spatial and seasonal distribution of effort, improved selectivity …) having a direct effect on fish stocks.
Both can then lead to longer term effects arising from changes in the relative abundance of different species or group of species.These effects are considered as“ecosystem effects” since they arise from the interactions between species and the change in energy flows through the system.
In this work package, using existing or developping modelling tools implemented across the DiscardLess case studies, we had two objectives:
Overall, the trophic models used found little effect of a discard ban (landing the fish previously discarded, with no changes in the fishing pressure) on the ecosystem, except for birds. On the other hand, not catching the fish that were previously discarded had a significant effect in our simulations, which confirms that the ecological effects of the Landing Obligation will be through reduced fishing pressure rather than anything else.
In the Eastern Channel, the 2 models used (Isis Fish and Osmose/DSVM) suggest that the implementation of the LO will benefit fish stocks, although in the case of Osmose/DVSM the biomass increases are buffered by trophic interactions, particularly through cod and whiting predations on other commercial species. Both models also suggest a long term benefit to fleets, following a 10 year long period of decreased revenues.
In the Bay of Biscay, the results of the FLBEIA bioeconomic model (WP2) have been used to drive forecast simulations with EwE, to analyze the status of the Bay of Biscay ecosystem in the short-medium term (from 2013 to 2024). The results illustrate “winners” and “losers” and particularly how seabirds and carnivorous benthic invertebrates are likely to be those suffering from the LO, while hake will increase its overall abundance.
Finally in the North Sea, the StrathE2E model was extended spatially and refined in terms of the description and dynamics of the fishing fleets. The general outcome is similar to what was stated in the previous version, i.e. simply changing discarding practices while fishing as usual, has a negligible conservation benefit at the level of the ecosystem as a whole. On the other hand, tacking the curtailment of discarding by reducing the capture of unwanted fish has the potential to deliver noticeable conservation benefits.