The demersal bathyal fish assemblage of the Central-Western Mediterranean: Depth distribution, sexual maturation and reproduction

Cristina Porcu

;Martina Francesca Marongiu;Antonio Olita;Andrea Bellodi;Rita Cannas;Pierluigi Carbonara;Alessandro Cau;Antonello Mulas;Paola Pesci;Maria Cristina Follesa

Ultimo

2020-01-01

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Abstract

This study compiles information on the size distribution and reproductive patterns of five chondrichthyans and 10 bony species dwelling on the continental slope of the Central-Western Mediterranean (south-eastern Sardinian waters, depth 720–1890 m). The abundance of the relatively less numerous chondrichthyans was found to decrease with depth. Almost all chondrichthyan species had a long reproductive period throughout the year at all depths. In bony fishes, the upper bathymetric stratum (<1100 m) was dominated by species with continuous and seasonal (autumn-winter) spawning cycles. At intermediate and lower depths (>1100 m), continuous repro- duction was the most common pattern. Both chondrichthyans and bony fishes exhibited large sizes at maturity and at first maturity (>75% and >60% of their maximum body length, respectively), supporting the hypothesis that most deep-sea fish populations are characterized by a delayed maturity, which makes them highly vulnerable to fishing pressure and over-exploitation. In some sharks, population partitioning was observed, according to life stage as a function of depth: adult/mature females occupied deeper habitats than males and juveniles. Conversely, Diptrs nidarosiensis female and male juveniles (>1100 m) were segregated from the adult/mature population, dwelling between 1000 and 1100 m. In four of the 10 bony fishes examined, we found a clear and significant predominance of females, particularly pronounced in Alepocepals rostrats, which is clearly related to their K-reproductive strategy. The four key-selected species (ales melastoms, A rostrats, atpterois mediterranes and racrincs scabrs), characterized by different reproductive strategies/modal- ities and feeding behaviours, were differently affected by depth and fluxes of organic matter (Particulate Organic Carbon concentration) from the photic zone towards the sea-bottom as a function of sex and life -stage.