Marine spatial closures as a supplementary tool to reduce discards in bottom trawl fisheries: Examples from southern European waters

Abstract

Discards is an important issue in fisheries around the world. The spatial management of discards has attracted interest as a potential tool for minimizing the unwanted catch. The aim of the present work was to identify areas with high quantities of bottom trawl discarded catch regarding species subjected to MCRS, in six areas of southern European waters (southern Portuguese waters, Catalan Sea, Ligurian and northern Tyrrhenian Seas, Strait of Sicily, eastern Ionian Sea, and Aegean Sea). Analyses were based on two types of data: (a) the undersized catch of species subjected to MCRS from bottom trawl surveys and (b) the actual discarded catch (including undersized and non-undersized individuals) of species subjected to MCRS from commercial bottom trawling. Geostatistical analysis techniques were applied to the first type of data and Generalized Additive Models using environmental variables were applied to the second one. Subsequently, areas that persistently presented high quantities of discarded catch (i.e., "iDC grounds") or undersized catch (i.e., "iUC grounds") were identified and mapped. The "iDC grounds"/"iUC grounds" were located either over the slope or within the continental shelf and over marine plateaus, largely depending on the main target species of each fishery. Next, the overlap of "iDC grounds"/"iUC grounds" with the existing Fisheries Restricted Areas (FRAs) and the proposed Marine Protected Areas (MPAs) was estimated aiming to explore how spatial closures could contribute to the reduction of bottom trawl discarded catch/undersized catch. Certain spatial closures were more effective in the Central Mediterranean and others to the Eastern Mediterranean. The overlapping of existing FRAs with "iDC grounds"/"iUC grounds" did not exceed 24 % in any study area, whereas proposed MPAs, like the CIESM Marine Peace Parks, reached up to 90 % for the same study area.

Identifying Persistent Hot Spot Areas of Undersized Fish and Crustaceans in Southern European Waters: Implication for Fishery Management Under the Discard Ban Regulation

“…From a biological point of view, the fishing fleet is distributed according to the distribution of the fishery resource, which in turn is distributed according to environmental characteristics that hardly change drastically over the time span used in this study, therefore also the distribution of the fishing fleet could be considered stable in the considered time. Furthermore, we are aware that the species considered in the present study do not cover all the species regulated by the MCRS or the TAC, but since they represent in some cases up to 90 percent of the under-sized fraction discarded (Despoti et al, 2020), our results may be considered representative of a generalizable trend. We found a quite high stability of the density hot spots of undersized juveniles as already observed for the nursery areas of these species in the North Mediterranean Sea (Colloca et al, 2015).…”

“…were selected, while blue whiting, Micromesistius poutassou, was considered in the Portuguese area only (Table 1). UCs percentage of the aforementioned species could reach values greater than 40% in the total catch (Moranta et al, 2000;Carbonell et al, 2003;Sánchez et al, 2004Sánchez et al, , 2007Tsagarakis et al, 2014;Milisenda et al, 2017b), and 90% of the total UCs (Despoti et al, 2020), being consequently classified as "high discard rate species" according to FAO (FAO, 2016), and largely representative of the discard produced (understood as undersize) in the investigated areas.…”

“…Under the current trawl net selectivity patterns used in southern European fisheries, undersized individuals of some important commercial species, such as European hake (Merluccius merluccius) and Atlantic horse mackerel (Trachurus trachurus), predominate in the discard (Milisenda et al, 2017b;Damalas et al, 2018;Despoti et al, 2020), especially during the recruitment period (FAO, 2016). The combined provisions of art.…”

How Can We Reduce the Overexploitation of the Mediterranean Resources?

“…Since undersized fishes of many large-sized species, such as M. merluccius, are highly vulnerable to the minimum mesh size enforced in the Mediterranean (40 mm square or 50 mm diamond) (Brčić et al, 2018;Mytilineou et al, 2018) and a further increase of the mesh size would lose shrimps, cephalopods, and medium-sized fish, the exploitation pattern can be enhanced through: (i) increasing the trawl net selectivity by adopting grids and separators that allow the undersized fish to escape (Coll et al, 2008;Massutí et al, 2009;Aydın and Tosunoglu, 2011;Vitale et al, 2018b); (ii) delaying the size/age of the first capture of juveniles through spatial and/or temporal closures to fisheries when and where the juveniles aggregate in order to improve the fraction of fish reaching sexual maturity (Caddy, 1999(Caddy, , 2009Fiorentino et al, 2003;Garofalo et al, 2011;Colloca et al, 2015;Despoti et al, 2020;Mytilineou et al, 2020;Milisenda et al, 2021); or (iii) a combination of the two approaches.…”

Pots as alternative and sustainable fishing gears in the Mediterranean Sea: an overview

“…In this basin, the LO aims at encouraging fishers to avoid areas or seasons characterized by large amounts of undersized / unwanted fish and to employ more selective gears. In recent years, the scientific community has been focusing trying to gain greater information on the spatial distribution of nursery areas of the main commercial species (Colloca et al 2015) and has proposed spatiotemporal closures to minimize the catch of specimens under the MCRS (Russo et al 2014;Despoti et al 2020). The General Fisheries Commission for the Mediterranean (GFCM) has also established the Fisheries Restricted Areas (FRAs) to protect these essential fish habitats (FAO 2020).…”