Sustainability 2023, 15, 2425. https://doi.org/10.3390/su15032425 www.mdpi.com/journal/sustainability Article When the Trawl Ban Is a Good Option: Opportunities to Restore Fish Biomass and Size Structure in a Mediterranean Fisheries Restricted Area Carlo Pipitone 1,† , Davide Agnetta 2,3,† , Arturo Zenone 4,† , Vincenzo Maximiliano Giacalone 5, *, Fabio Badalamenti 1,3 , Fabio Fiorentino 4,6 , Paola Rinelli 7 , Mauro Sinopoli 4 , Tomás Vega Fernández 8 and Giovanni D’Anna 9 1 CNR-IAS, Lungomare Cristoforo Colombo 4521, 90149 Palermo, Italy 2 OGS, Via Beirut 2, 34151 Trieste, Italy 3 NBFC, National Biodiversity Future Center, 90133 Palermo, Italy 4 Stazione Zoologica Anton Dohrn, Lungomare Cristoforo Colombo 4521, 90149 Palermo, Italy 5 CNR-IAS, Via del Mare 3, 91021 Campobello di Mazara, Italy 6 CNR-IRBIM, Via Luigi Vaccara 61, 91026 Mazara del Vallo, Italy 7 CNR-IRBIM, Via San Ranieri 86, 98122 Messina, Italy 8 Stazione Zoologica Anton Dohrn, Villa Comunale, 80121 Napoli, Italy 9 CNR-IAS, Via Giovanni da Verrazzano 17, 91014 Castellammare del Golfo, Italy * Correspondence: vincenzomaximiliano.giacalone@cnr.it † These authors contributed equally to this work. Abstract: This paper reports the results of a 15-year trawl ban imposed in 1990 in the Gulf of Cas- tellammare (GCAST: NW Sicily, central Mediterranean Sea) and its effects on the biomass and size structure of demersal finfish and shellfish and on the proportion of different commercial categories of fish. Data were collected by experimental trawl surveys conducted in the GCAST and in two trawled areas before and after 1990. The biomass of the total assemblage and of a number of selected species was significantly higher in the GCAST after the ban. Highly commercial species had the largest increase in the same gulf after the ban, particularly at the depths used by artisanal fishermen. The results from size-based indicators were not as clear-cut as those from biomass though. Although the length frequency distributions obtained in the GCAST were significantly different from the other gulfs, in several cases, the values of the size indicators were higher in the trawled gulfs. Our results suggest that, at the temporal and spatial scale adopted, trawl bans may drive full biomass recovery but only partial size structure recovery of the fish populations subject to trawl exclusion, at least in the Mediterranean. The trawl ban in the Gulf of Castellammare provides an example of an effective ecosystem-based fisheries management tool that offers the potential for fish stock re- building and for the economic sustainability of artisanal, small-scale fisheries. Keywords: spatial management; fishery closure; size structure; fish biomass recovery; small-scale fisheries; sustainable fisheries; trawlable fish assemblage 1. Introduction Fishing activities and, in particular, bottom trawling directly and indirectly affect fish assemblages and cause a number of undesirable consequences on fish populations such as reduced biomass, truncated size structures, and disrupted food webs, with a large part of world stocks falling in the range between fully exploited to depleted [1–6]. Fisheries management aiming at sustainable yields through approaches based on catch quota and control of fishing effort have proved generally effective when applied to monospecific fisheries [7,8] and even then, stock collapses have occurred with dramatic consequences [9]. Multispecies fisheries, which dominate in warm-temperate and tropical regions, are Citation: Pipitone, C.; Agnetta, D.; Zenone, A.; Giacalone, V.M.; Badalamenti, F.; Fiorentino, F.; Rinelli, P.; Sinopoli, M.; Vega Fernández, T.V.; D’Anna, G. When the Trawl Ban Is a Good Option: Opportunities to Re-store Fish Biomass and Size Structure in a Mediterranean Fisheries Restricted Area. Sustainability 2023, 15, 2425. https:// doi.org/10.3390/su15032425 Academic Editors: Vesselina Mihneva, Violin St. Raykov and Pablo Pita Received: 25 October 2022 Revised: 19 January 2023 Accepted: 26 January 2023 Published: 29 January 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and con- ditions of the Creative Commons At- tribution (CC BY) license (https://cre- ativecommons.org/licenses/by/4.0/).