In this study, the taxonomic resolution and phylogenetic relationship of two presumed subspecies of Merlangius merlangus, namely M. m. euxinus and M. m. merlangus, were investigated. In addition, the effect of the Turkish Straits System on the evolutionary history and genetic structure of M. merlangus, was explored. The mitochondrial cytochrome c oxidase subunit 1 and cytochrome b genes, and the nuclear recombination activating gene-1 were analysed. Our results indicate no clear distinction between the two presumed subspecies, which is attributed to the low resolution of recombination activating gene-1 and/or presence of potential gene flow between the two subspecies. The temporal pattern of divergence between the two presumed subspecies related to the Last Glacial Maximum (219 Kya), whereas the expansion of each main sampling location occurred after the flooding of the Black Sea by salt water from the Mediterranean (5 Kya), following a period of stability. Additionally, significant genetic differences are observed among the North Aegean samples and the collections from the Turkish Straits System and the Black Sea, along with some significant structure among sampling sites located in the Turkish Straits System and Black Sea. The lower genetic variability of the eastern Mediterranean M. merlangus when compared to Atlantic ones might be due to a potential population bottleneck before the last glacial period, a trend that is commonly found in these waters.

In this study, molecular taxonomy associated with Spicara flexuosa, Spicara maena, and Spicara smaris was examined with a geographical focus along the coasts of the Turkey and the Mediterranean. In addition, the effects of the Turkish Straits System on the evolutionary history and phylogeography of Spicara flexuosa were investigated.The mitochondrial cytochrome c oxidase I, cytochrome b, and the nuclear Interphotoreceptor retinoid-binding protein genes were used for these purposes. Our results indicated that the distinction of the three taxa under Spicara is possible with the two different mitochondrial DNA markers. Nuclear DNA analyses indicated that reproductive isolation of the S. maena and S. flexuosa was complete. Demographic analyses support the sudden population growth of S. flexuosa after a potential bottleneck. The result of the dating analyses suggested that the three Spicara species were differentiated during the early or middle Pliocene. An absence of genetic structure between Spicara flexuosa subpopulations from Turkey indicated the connectivity, within sampling locations, suggesting that the Turkish Straits System is a corridor for gene flow for this species. As picarel populations have experienced rapid decline in their distribution areas in recent years, separate population studies are necessary to help make informed conservation and management decisions for S. maena and S. flexuosa.

Length-weight relationships and condition factors of Spicara flexuosa collected from Turkish coastal waters were evaluated in this study. The results indicated that samples collected from Istanbul and Çanakkale exhibited positive allometric growth while S. flexuosa showed negative allometric growth in Rize and Sinop-Kastamonu in December 2013 and January 2014 respectively. The minimum total length was found in Istanbul (11.04 cm), and the maximum total length (19.50 cm) was found in Sinop-Kastamonu and the minimum (15 g) and maximum weight (102 g) were collected from Istanbul (Bosphorus Strait) in February 2014. The overall length-weight equation (W=0.0236L2.7334) indicated negative allometric growth from all sampling periods. The relative condition factor among regions varied from 0.99 to 1.08, indicating a state of wellbeing among all locations. On the other hand, overall condition value was found smaller than one. This study provides the baseline data of length-weight relationships and condition factor analyses for S. flexuosa species from Turkish coastal waters for future management purposes for this species.

In the present study, intraspecific morphometric distribution of Spicara flexuosum was investigated along the five locations on the Turkish coast based on eight morphological characters. A total of 116 samples were obtained along the Turkish coasts (Istanbul, Yalova [Armutlu], Izmir, Mersin and Antalya) by using trawlers and the handline fishing method within the period in 2014–2015. Principal component analysis and the dendrogram-based Euclidean distance method were used to evaluate different morphometric traits among five locations. The most important ratios of the morphometric loading characters were the head length to interorbital distance, head length to eye diameter, maximum body height two to head height, and head height to head length. The classification matrix based on the discriminant function analysis showed that 94.7% of original grouped were correctly classified. Principal component and cluster analysis showed the existence of two morphologically differentiated groups of S. flexuosum. First one composed of Istanbul and Yalova and the second one consisted of Izmir, Mersin and Antalya. This study is the first description of the intraspecific distribution of morphometric characters for S. flexuosum along the Turkish coast as well as the Mediterranean region for fisheries management purposes.