Biological evidence of the presence of different subpopulations of Norway lobster (Nephrops norvegicus) in the Adriatic Sea (Central Mediterranean Sea)

Abstract

Norway lobster (Nephrops norvegicus) is one of the most important crustacean species in terms of landings and commercial value for the Adriatic Sea. In this zone, this stock is composed by two different subpopulations, characterised by different growth features. This study focus on the biology of individuals from the two most important fishing grounds of the area, namely the “off Ancona” area and the Pomo/Jabuka pits. The size at the onset of first maturity (SOM) for both males and females were determined by means of macroscopic techniques: gonad tissue was examined for females, whereas the relation between carapace length and appendix masculina (length and width) was investigated for males. The estimated SOMs underline the differences between these two subpopulations, even if only the relationship between the carapace length and the length of the appendix masculina of the Pomo/Jabuka pits is statistically sound. Males from the Pomo/Jabuka pits mature at carapace length (CL) between 24.33 ± 0.32 and 25.39 ± 0.81 mm, corresponding to the SOM estimated respectively from the length and the width of the appendix masculina. Estimated L50 for females is 21.14 mm CL within the Pomo/Jabuka pits and 30.83 mm CL in the “off Ancona” area. These results underline the fact that the subpopulations living in the “off Ancona” fishing ground matures at bigger length compared to that one inhabiting the Pomo/Jabuka pits. This is in line with the other analysis carried out within this study, that show the presence of larger individuals in the “off Ancona” fishing ground, whereas small individuals characterize the Pomo/Jabuka pits. These differences have to be taken into account when managing this stock.