Scientific progress made towards bridging the knowledge gap in the biology of Mediterranean marine fishes

The Mediterranean Sea is a renowned biodiversity hotspot influenced by multiple interacting

ecological and human forces. A gap analysis on the biology of Mediterranean marine fishes

was conducted in 2017, revealing the most studied species and biological characteristics,

as well as identifying knowledge gaps and areas of potential future research. Here, we

updated this gap analysis five years later by reviewing the literature containing information

on the same eight biological characteristics, namely length-weight relationships, growth,

maximum age, mortality, spawning, maturity, fecundity and diet, for the 722 fish species of

the Mediterranean Sea. The results revealed a considerable knowledge gap as 37% of the

species had no information for any of the studied characteristics, while 13% had information

on only one characteristic. Out of all the biological characteristics, the smallest knowledge

gap was found in the length-weight relationships (studied for 51% of the species, mainly in

the eastern Mediterranean), while the least studied characteristic was mortality (studied for

10% of the species). The western and eastern Mediterranean Sea were leading forces in

data collection exhibiting the narrowest gaps between current and desired knowledge. The

most studied species across the entire region were the highly commercial European hake

(Merluccius merluccius), red mullet (Mullus barbatus), European anchovy (Engraulis encrasicolus),

European pilchard (Sardina pilchardus), common pandora (Pagellus erythrinus),

and annular seabream (Diplodus annularis). The knowledge gap has shrunk by 6% during

the last five years, with 40 new species having at least one study on their biology. Moreover,

research has slightly shifted towards species that have been traditionally neglected, e.g.,

sharks, rays and chimaeras (chondrichthyans). It is recommended that research becomes

less focused on commercial species and more targeted towards the identified gaps, vulnerable

species (e.g., deep-sea species and chondrichthyans) and species that could potentially

pose a threat (e.g., non-indigenous species) to the ecosystems of the everchanging Mediterranean

Sea.