Efficient fisheries management requires the anticipation of dynamics of exploited ecosystems, the fishing fleets harvesting them, and their interaction. A common driver of fishers' behaviour is the spatial distribution of the resources they exploit. Subject to market conditions and regulatory constraints, fishers are expected to cost-efficiently visit fishing grounds with a high density of targeted species and/or marketable size classes. In doing so, they may also catch and be forced to discard unwanted species or sizes they cannot market and/or are subject to regulatory measures. Within European Union (EU) fisheries, the 2015 reform of the Common Fisheries Policy saw the gradual implementation of the Landing Obligation, which aimed at reducing discards, although the extent to which has succeeded has been questioned.
In this Editor's Choice article, Marchal and Vermard combined three large eastern English Channel datasets to investigate how spatial overlap between the distributions of fishing effort, commercial species, and discard rates can describe species targeting, how species and/or size compositions determine discarding, and whether potential discard hotspot areas are avoided by fishers.
The authors found that species that are not regulated by Total Allowable Catches (TAC), such as cuttlefish (Sepia officinalis), squids (Loligo sp.), striped red mullet (Mullus surmuletus), and sea bass (Dicentrarchus labrax) drove fishing effort distribution to a large extent. In contrast, fishing for historically important TAC-regulated species, for example, cod (Gadus morhua) and whiting, has become less attractive. This was broadly consistent with landing compositions, although mackerel (Scomber scombrus) targeting was likely underestimated. They also showed that the distributions of fishing effort of undersized herring, plaice, and whiting did not overlap. Although fishing effort covered fishing grounds populated with undersized horse mackerel, the proportion of undersized individuals in the discards was small. In contrast, plaice and whiting discards were essentially undersized, and overlapped in space with undersized abundance indices. Fishing effort may have avoided spatial units with potentially high plaice discard rates, although no link with the implementation of the EU Landing Obligation could be found.
All in all, results generally show consistency between the distributions of targeted species and fishing effort, and also that undersized discard hotspots occurred on fishing grounds populated with small plaice (Pleuronectes platessa) and whiting (Merlangius merlangus). Discards avoidance was variable over the years and species, and unrelated to the implementation of the EU Landing Obligation.
Read the full paper, Species targeting and discarding in mixed fisheries, in ICES Journal of Marine Science.
Editor's Choice articles are always free to read in ICES Journal of Marine Science.
Commercial catch sampling within the Ifremer-led OBSMER programme: a fruitful industry-science partnership. © Ifremer/Olivier Dugornay