Age and growth of <i>Pecten jacobaeus</i> in the eastern Adriatic Sea – why location matters?

Bivalves deposit shell material during their lifetime, and many species’ growth patterns and age can be determined from their growth increments. Shell growth varies through ontogeny and can also have temporal and spatial variations dependent on the environmental conditions. Some scallop species (family Pectinidae) have clearly visible annual growth lines on the external surfaces of their shells that enable reliable analysis of growth patterns. Pecten jacobaeus , a commercially important scallop species that lives in Mediterranean coastal waters, is one of them. In this study, we analysed variations in growth and age of P. jacobaeus specimens collected from five locations in the eastern part of the Adriatic Sea. To obtain insights into spatial variations in feeding ecology, nitrogen and carbon isotopes were analysed in mussel tissues. Sampling was conducted in late 2023 and the first half of 2024, and between 45 and 60 specimens were collected at each location. In the northeast Adriatic (Istria), samples were collected by beam trawl fishing vessels, while at other locations (Iž, Maslenica, Prokljan, Pelješac) SCUBA divers were engaged. The shell length of analysed specimens varied from 44.6 to 149.5 mm, while their estimated age ranged from one to 12 years. The data on age and shell length were fitted to the von Bertalanffy growth function. Growth was also estimated using the Gulland-Holt plot, and a relative growth functions were constructed. Results of this study contribute to the understanding of P. jacobaeus growth dynamics and have potential applications in fisheries management and conservation.