Commercial catches and discards composition in the central Tyrrhenian Sea: a multispecies quantitative and qualitative analysis from shallow and deep bottom trawling

Abstract

In the Mediterranean Sea, the catch of bottom trawl fisheries is composed of a complex mix of fish and invertebrates with a considerable amount of discards. Seasonal composition of catches and discards of bottom trawls operating at different depths in the central Tyrrhenian Sea were investigated from October 2014 to October 2015. The mean total catch per unit effort (CPUE) ranged between 30.93±8.43 and 27.52±9.88 kg/h in shallow and deep fishing grounds, respectively. The discarded fraction of the catch was 39.9 % in shallow and 43.3% in deep fishing grounds. The mean CPUE of commercial target species were similar in shallow and deep trawling (10.81+5.82 vs 8.92±3.16 kg/h). The commercial bycatch was lower in shallow (6.66±1.25 kg/h) than in deep grounds (8.24±2.91 kg/h), whilst the discards were lower in deep (10.43±5.14 kg/h) than shallow grounds (13.43±5.29 kg/h). Overall, 246 species were caught during fishing operations, out of which 209 were included in discards. The number of species recorded in shallow grounds (199 caught species with 166 discarded) was higher than that recorded in deep grounds (116 caught species with 102 discarded). Fish were the most represented taxa in the shallow discards, followed by echinoderms; crustaceans, and were the main discarded taxa in deep water. Depth was the main factor affecting both commercial catches and discards composition, whereas the season affected the CPUE of main target species only. The results confirmed that discards were higher in shallow than in deep trawling, suggesting that the latter is more efficient than the former in catching fishery resources for human consumption. Understanding the factors that affect discarding is the starting point for adopting management measures to mitigate negative impacts of trawl fisheries on marine resources and benthic communities.

Net gain: Low‐cost, trawl‐associated eDNA samplers upscale ecological assessment of marine demersal communities

“…Here, we found a distribution of species read abundances consistent with previous knowledge on demersal fish assemblages in the Mediterranean Sea (Russo et al, 2019). Many of the species most frequently found in landings of bottom trawlers in the central Tyrrhenian Sea (Russo et al, 2016;Tiralongo et al, 2021) were among the most abundant in terms of number of reads in our eDNA metabarcoding data; the European hake (Merluccius merluccius), was the most represented species in both COI and 12S data (Figure 5a Sea (Bradai et al, 2012), was among the most abundant species in both the 12S and the COI datasets, coherently with the available knowledge for the area of study (Sbrana et al, 2022).…”

“…Here, we found a distribution of species read abundances consistent with previous knowledge on demersal fish assemblages in the Mediterranean Sea (Russo et al, 2019). Many of the species most frequently found in landings of bottom trawlers in the central Tyrrhenian Sea (Russo et al, 2016; Tiralongo et al, 2021) were among the most abundant in terms of number of reads in our eDNA metabarcoding data; the European hake ( Merluccius merluccius ), was the most represented species in both COI and 12S data (Figure 5a,b). Concerning invertebrates, the giant red shrimp ( Aristaeomorpha foliacea ), the deep water rose shrimp ( Parapenaeus longirostris ), the Norway lobster ( Nephrops norvegicus ) and the blue and red shrimp ( Aristeus antennatus ), key target species of trawlers during spring and summer in the central Tyrrhenian Sea, were all in the 10 top species of Figure 5c.…”

“…COI metabarcoding not only informed on the complex assemblages of cephalopods and crustaceans but also yielded a complement 42% fish species in addition to the 12S detections (Figure S2). Interestingly, many of the most important target species for demersal catches in the Tyrrhenian Sea (Russo et al, 2016;Tiralongo et al, 2021) were among the most abundant species in our eDNA metabarcoding data.…”

First evidence of population genetic structure of the deep-water blackmouth catshark Galeus melastomus Rafinesque, 1810

“…This research work revealed the first evidence of a detectable genetic structure of the necto-benthic, deep-water G. melastomus populations in the Mediterranean Sea and neighbouring North-East Atlantic areas, whose stocks are potentially affected and impacted by the demersal fishery (Tiralongo et al, 2021). Here, we described the first evidence of a weak albeit detectable genetic structure and the development of a technological tool represented by a panel of cross-specific microsatellite loci which were successful in detecting and measuring species genetic diversity and differentiation of blackmouth catshark over a large, regional geographic scale and a significant number of samples and individuals.…”

First evidence of in vitro cytotoxic effects of marine microlitter on Merluccius merluccius and Mullus barbatus, two Mediterranean commercial fish species

“…The presence of both shape types in the stomach of M. merluccius and M. barbatus and the lack of statistically significant differences based on the chromatic factor support the idea that microlitter may be ingested non-selectively by these two species, even though a biomagnification origin cannot be excluded. Hake and mullet were chosen as experimental models for a variety of reasons: on one hand they are among the most targeted demersal fish species by the Mediterranean deep-sea fisheries and the two most fished target species in the shallow area of the coastal sector (Sabatella et al, 2017;Tiralongo et al, 2021); on the other, they are regarded as bioindicators in coastal marine ecosystems and display a benthic feeding behavior in part of (juvenile M. merluccius) or throughout their lifespan (M. barbatus) (Carrozzi et al, 2019;Esposito et al, 2014). Moreover, some authors already described the occurrence of MPs in these two species (Atamanalp et al, 2021;Avio et al, 2015;Bellas et al, 2016;Digka et al, 2018;Giani et al, 2019;Mancuso et al, 2019) and MPs were demonstrated to abound in superficial sediments in the study area (Piazzolla et al, 2020).…”