Spatial variability of Chondrichthyes in the northern Mediterranean

Abstract

Thanks to the availability of the MEDITS survey data, a standardized picture of the occurrence and abundance of demersal Chondrichthyes in the northern Mediterranean has been obtained. During the spring-summer period between 2012 and 2015, 41 Chondrichthyes, including 18 sharks (5 orders and 11 families), 22 batoids (3 orders and 4 families) and 1 chimaera, were detected from several geographical sub-areas (GSAs) established by the General Fisheries Commission for the Mediterranean. Batoids had a preferential distribution on the continental shelf (10-200 m depth), while shark species were more frequent on the slope (200-800 m depth). Only three species, the Carcharhiniformes Galeus melastomus and Scyliorhinus canicula and the Torpediniformes Torpedo marmorata were caught in all GSAs studied. On the continental shelf, the Rajidae family was the most abundant, being represented in primis by Raja clavata and then by R. miraletus, R. polystigma and R. asterias. The slope was characterized by the prevalence of G. melastomus in all GSAs, followed by S. canicula, E. spinax and Squalus blainville. Areas under higher fishing pressure, such as the Adriatic Sea and the Spanish coast (with the exception of the Balearic Islands), show a low abundance of chondrichthyans, but other areas with a high level of fishing pressure, such as southwestern Sicily, show a high abundance, suggesting that other environmental drivers work together with fishing pressure to shape their distribution. Results of generalized additive models highlighted that depth is one of the most important environmental drivers influencing the distribution of both batoid and shark species, although temperature also showed a significant influence on their distribution. The approach explored in this work shows the possibility of producing maps modelling the distribution of demersal chondrichthyans in the Mediterranean that are useful for the management and conservation of these species at a regional scale. However, because of the vulnerability of these species to fishing exploitation, fishing pressure should be further incorporated in these models in addition to these environmental drivers.

Species diversity, taxonomy and distribution of Chondrichthyes in the Mediterranean and Black Sea

“…Taking into account the demersal species collected during the scientific trawl surveys (e.g., MEDITS surveys), which has systematically sampled European Mediterranean Waters since 1994, some species were commonly recorded in both the Mediterranean and the Black Sea (S. canicula; R. clavata; S. acanthias, etc. Relini et al 2000;Massutí & Moranta 2003;Sion et al 2004;Massutí & Reñones 2005;Megalofonou et al 2005;Serena 2005Serena , 2007Serena et al 2009;Damalas & Vassilopoulou 2011;Ragonese et al 2013;Tserpes et al 2013;Ramírez-Amaro et al 2015;Abella et al 2017aAbella et al , 2017bAbella et al , 2017cAbella et al , 2017dMelendez et al 2017;Bradaï et al 2018;Follesa et al 2019). In general, within the framework of the (MEDITS) trawl surveys, 45 species of chondrichthyans (18 sharks, 2 angel sharks, 4 stingrays, 3 skates, 14 rays, 3 electric rays, and 1 chimaera) were recorded and included in a taxonomic list (Anonymous 2017).…”

“…In the last 50 years, monitoring programs aimed at evaluating the status and distribution of Mediterranean demersal resources promoted the collection of information on chondrichthyan presence and abundance that are useful to detect anthropogenic impact and changes in marine communities (Quignard & Capapé 1971;Fredj & Maurin 1987;Aldebert 1997;Moranta et al 1998;Bertrand et al 2000;Megalofonou et al 2000;Relini et al 2000;Jukic-Peladic et al 2001;Garofalo et al 2003;Schembri et al 2003;Fromentin & Farrugio 2005;Relini et al 2010a;Serena et al 2011;Maravelias et al 2012;Tserpes et al 2013;Follesa et al 2019). However, there are still knowledge gaps for both species richness and abundance of sharks, batoids and chimaeras in the different sectors of the Mediterranean Sea.…”

Living naked: first case of lack of skin‐related structures in an elasmobranch, the blackmouth catshark (Galeus melastomus)

“…ap: ampullary pore; bp: basal plate; dd: dermal denticle; de: dermis; e: epidermis; m: melanocyte; rdd: rudimental dermal denticle; s: spine; sco: stratum compactum; slax: stratum laxum G. melastomus is a common, small-sized catshark belonging to the family Pentanchidae that reaches a maximum total length (L T ) of about 70 cm (Serena et al, 2009). It is widely distributed in the Northeast Atlantic and Mediterranean Sea at depths of 50-2000 m, although mostly abundant from 200 to 500 m (Follesa et al, 2011;Follesa, Marongiu, et al, 2019;Serena et al, 2009), and represents a common by-catch species with very low or no commercial value (Marongiu et al, 2017;Serena et al, 2009).…”

Growth and Age Validation of the Thornback Ray (Raja clavata Linnaeus, 1758) in the South Adriatic Sea (Central Mediterranean)

“…In the South Adriatic Sea, the thornback ray is caught mostly by bottom longlines targeting the European hake and bottom trawls with mixed target fishes (Merluccius merluccius and Mullus barbatus) and crustacean decapods (Parapaeneus longirostris and Nehrops norvegicus) (Maiorano et al, 2019). Living in a wide bathymetric range (Krstulović-Šifner et al, 2008;Marongiu et al, 2017;Follesa et al, 2019b), the thornback ray is accessible to different fishing métiers (International Council for the Exploration of the Sea [ICES], 2018). Moreover, like most elasmobranchs, R. clavata exhibits a k-selected strategy, which is characterized by slow growth rate, long life spans, late-age sexual maturity, and low fecundity (Gallagher et al, 2005;Whittamore and McCarthy, 2005;Kadri et al, 2014), which makes the species particularly vulnerable to fishing exploitation.…”