Growth, reproduction, and potential factors involved in body size reduction of poor cod (Trisopterus capelanus) in the northern Adriatic Sea

The poor cod (Trisopterus capelanus) is a gadoid endemic species of the Mediterranean and Black Seas showing fast growth and early sexual maturity. It accounted for 3–10 % of the total catch biomass of the Italian trawling fleet in the early ‘90s. However, its abundance has decreased significantly over the past two decades, with most of the landings occurring in the Adriatic Sea. The aims of the present study are to update information about the biological parameters of poor cod in the northern Adriatic Sea, to compare the size/age structure and growth performance of populations sampled with an interval of 34 years, to discuss the outcomes of the comparison taking into account the potential effects of fishing pressure and sea warming. Fish samples were collected monthly from commercial bottom trawlers of the northern Adriatic Sea in 2020–2021 and the growth performance of this population was compared with data coming from a previous sampling carried out in 1986–1987 in a nearby area. Age estimations were performed using data from age readings of thin otolith sections. Sexual maturity was achieved within the first year of life, at around 12 cm TL for males and 13 cm TL for females. The growth and age structure of the poor cod from the northern Adriatic Sea revealed some differences in the growth trajectories between the sampling periods, showing a reduction in the asymptotic length in both sexes. Despite some limitations due to the comparative approach, we hypothesize that the decreased growth performance might be related to metabolic constraints, possibly related to the increased temperature and/or high levels of fishing exploitation.