Bio-Ecological Features Update on Eleven Rare Cartilaginous Fish in the Central-Western Mediterranean Sea as a Contribution for Their Conservation

Abstract

Cartilaginous fish are commonly recognized as key species in marine ecosystems for their fundamental ecological role as top predators. Nevertheless, effective management plans for cartilaginous fish are still missing, due to the lack of knowledge on their abundance, distribution or even life-history. In this regard, this paper aims at providing new information on the life-history traits, such as age, maturity, reproductive period, in addition to diet characteristics of eleven rare cartilaginous fish inhabiting the Central-Western Mediterranean Sea belonging to the orders Chimaeriformes (Chimaera monstrosa), Hexanchiformes (Heptranchias perlo and Hexanchus griseus), Myliobatiformes (Aetomylaeus bovinus and Myliobatis aquila), Rajiformes (Dipturus nidarosiensis and Leucoraja circularis), Squaliformes (Centrophorus uyato, Dalatias licha and Oxynotus centrina) and Torpediniformes (Tetronarce nobiliana), useful for their assessment and for future management actions. Particularly, the present paper provides for the first time the age estimation of D. nidarosienis and L. circularis which were both found capable of becoming older than ten years. In addition, the present study updates the sizes of first maturity of C. uyato and D. licha, which appeared to be capable of reproducing earlier than what was previously hypothesized, representing very valuable information for a better understanding of these rare species populations status and, eventually, their conservation. On the basis of the stomach content analysis, it was possible to identify five different predator groups.

Jaws from the deep: biological and ecological insights on the kitefin shark Dalatias licha from the Mediterranean Sea

“…Such spatial segregation has been proposed as a mechanism to increase the efficiency of the reproductive effort, while minimising the risk of cannibalism and depredation of juveniles and sub-adults by mature individuals (Moura et al, 2014). Such spatial segregation would also explain the dominance of females at deeper depths in Sardinian waters, (Mulas et al, 2021).…”

“…Recent studies have described some life traits of this deep-sea shark, yet the biology and ecology remain unknown, making the development of effective management and conservation actions difficult (Capapéet al, 2008;Navarro et al, 2014;Barrıá et al, 2015;de Loyola Fernańdez et al, 2017;Barrıá et al, 2018;Booth et al, 2020;Mulas et al, 2021).…”

Ontogenetic Shifts in Body Morphology of Demersal Sharks’ Species (Order: Squaliformes) Inhabiting the Western-Central Mediterranean Sea, with Implications for Their Bio-Ecological Role

“…This area, due to its peculiar geographic position of being located in the centre of the Western Mediterranean basin, is often considered to be a hotspot for demersal shark biodiversity and abundance [ 22 , 23 , 24 ]. In addition to the velvet belly lanternshark ( Etmopterus spinax (Linnaeus, 1758)), the longnose spurdog ( Squalus blainville (Risso, 1827)), and the little gulper shark ( Centrophorus uyato (Rafinesque, 1810)), which are considered common species in the area, two rare and poorly known species were also investigated: the kitefin shark ( Dalatias licha (Bonnaterre, 1788)) and, notably, the angular roughshark ( Oxynotus centrina (Linnaeus, 1758)) [ 25 , 26 ]. Furthermore, an entire body morphometrical analysis was followed by a more in-depth shape analysis of the caudal fin, yielding the most comprehensive scenario regarding the effect of changes in body proportions during ontogenetic growth on the ecological role of these important species.…”

First documented record of neonate angular roughshark Oxynotus centrina from the eastern Adriatic Sea

“…Further, a neonate specimen (225 mm TL) was previously reported from Bozcaada Island (in the north-eastern Aegean Sea) (Eryilmaz, 2003). Moreover, reports of similar-size neonates were also provided by Kabasakal (2010), Mulas et al (2021) and Gul et al (2022). Their occurrence appears to be rare in the entire Mediterranean basin, with a very small number of published records.…”

“…Such an increase in the number of records might be a result of the more intense usage of citizen science in recent years, as half of the records provided in Gajić et al (2021) come either from direct reports from fishers or from social networks. On the other hand, studies that indicate a very narrow feeding niche, characterized by the consumption of elasmobranch eggs (Guallart et al, 2015;Mulas et al, 2021) could also explain the rarity of this species. If the validity of this diet can be proved by further studies, it could help explain species rarity, as such a narrow niche is unlikely to support a larger number of individuals in the ecosystem, due to the relatively limited availability of food resources.…”