Abundances of Demersal Sharks and Chimaera from 1994-2009 Scientific Surveys in the Central Mediterranean Sea

Abstract

Bibliographic and data gathered in scientific bottom trawl surveys carried out off the Southern Coasts of Sicily (Mediterranean Sea), from 1994 to 2009 and between a depth of 10 and 800 m, were analysed in order to prepare a checklist of demersal sharks and chimaera, which are species sensitive to fisheries exploitation. Out of the 27 previously reported demersal shark and chimaera taxa in the Mediterranean, only 23 were found in literature and 20 sampled during the surveys in the investigated area. Among the species sampled in the surveys, only 2 ubiquitous ( Squalus blainville and Scyliorhinus canicula ) and 3 deep-water ( Chimaera monstrosa , Centrophorus granulosus and Galeus melastomus ) species showed a wide geographical distribution with a consistent abundance. Excluding the rare (such as Oxynotus centrina ) or uncommon shark (e.g. Squalus acanthias ), the estimated frequencies of occurrence and abundance indexes show a possible risk of local extinction for the almost exclusively (e.g. angelshark, Squatina spp.) or preferential (e.g. Scyliorhinus stellaris ) neritic species.

A Tale on the Demersal and Bottom Dwelling Chondrichthyes in the South of Sicily through 20 Years of Scientific Survey

“…As observed worldwide, also in the above-reported area, bottom trawls are increasing in size, power and efficiency, as well as in their fishing activities, mainly towards the offshore grounds (in Ref. [4]). Due to the bycatch nature and high discard rate, long-term sources of information to assess Chondrichthyes gross catch are very limited in this region.…”

“…However, Sicilian fishers do distinguish between the two 'forms', which are often landed and commercialized (in Ref. [4]). …”

“…It is immediately discarded to the sea by fishers from Mazara because they think it will bring bad luck (in Ref. [4]). …”

“…Generally, they form small local stock (the so-called stock-let) with limited or low connectivity to each other (in Refs. [3][4][5]). The assumption that marine fish are not vulnerable to extinction because they live in open seas where their movements are unlimited is unfounded.…”

<b>On the taxonomy of the first record of rare deep-water rough shark species of Oxynotidae (Chondrichthyes: Squaliformes) in the western Indian Ocean</b>

“…It inhabits muddy and coralline algal bottoms of continental and insular shelves and upper continental slopes between 40-800 m depth, and is occasionally caught as bycatch during trawls and longlining (Ebert & Stehmann 2013;Ragonese et al 2013;Compagno 2016). This species occurs throughout the Eastern Atlantic Ocean from Norway to the western coast of South Africa (Bass et al 1976;Cadenat & Blache 1981;Ebert & Stehmann 2013;Ebert 2015;Compagno 2016 Fricke et al (2018) inaccurately listed this species as from off northern Madagascar, representing the first official record of Oxynotidae in the region, but again without detailed taxonomic information.…”