Assessing stock discrimination and exploitation status of an emerging Sardinella aurita fishery in the Bizerte Lagoon (Tunisia) in a changing climate

Title : Assessing stock discrimination and exploitation status of an emerging Sardinella aurita fishery in the Bizerte Lagoon (Tunisia) in a changing climate

Abstract:

Coastal lagoons are critical yet vulnerable ecosystems that serve as essential fishing grounds and nurseries for marine species. The Bizerta Lagoon in Tunisia, a regional hub, has recently experienced a dramatic and unexplained increase in the number of round sardinella (Sardinella aurita) caught, rising from 30 kg in 2014 to 25,171 kg in 2023. This signals a significant shift in the ecology and fisheries of these resources.

The aim of this study is threefold: to determine the stock structure of S. aurita between the lagoon and the adjacent sea; to assess its current exploitation status; and to discuss the potential environmental and management drivers behind this population expansion.

Stock discrimination was performed using otolith contour shape analysis (geometric morphometrics) on samples from the Bizerta Lagoon and the Mediterranean Sea. The fishery status was assessed using length-based (LBB) and catch-based (CMSY++) stock assessment models.

Otolith analysis revealed two distinct morphotypes, confirming the existence of two separate stocks inhabiting the lagoon and marine environments. Both assessment models indicated that the lagoon stock is not currently overfished. However, the average catch length (20.65 cm) far exceeds the length at first sexual maturity (14.3 cm).

This study provides the first evidence of a distinct, under-exploited stock of S. aurita in Bizerta Lagoon. The spectacular increase in catches, likely driven by climate-mediated environmental changes that have created favourable conditions, presents a critical case study of climate adaptation in coastal fisheries. We recommend implementing a bespoke monitoring and adaptive management programme to secure this emerging resource as a sustainable opportunity for Tunisian small-scale fisheries. This could provide valuable insights into the management of changing lagoon ecosystems worldwide.

Biography:

Professor Sami MILI is a distinguished scholar and administrator in the fields of fisheries science and aquatic ecosystems. He completed his foundational studies in June 2001, earning a Bachelor of Science in Natural Sciences from the Faculty of Sciences in Bizerte, Tunisia. He further advanced his expertise with a Master’s degree in Aquatic Ecosystem Production, obtained in March 2004 from the National Agronomic Institute of Tunisia (INAT) in collaboration with the National Institute of Marine Sciences and Technologies (INSTM). In September 2013, Professor MILI attained his Ph.D. in Fisheries Science through a joint program between INAT and INSTM, solidifying his academic and research credentials. Professionally, he served from 2017 to 2024 as the General Director of the Higher Institute of Fisheries and Aquaculture of Bizerte (ISPAB), where he oversaw academic and strategic development. Since January 2025, he has held a professorship at the Faculty of Sciences of Bizerte, contributing to education and research in marine and environmental sciences. He is also an active contributor to the scientific community, serving as an editorial board member for several peer-reviewed journals specializing in aquaculture, marine biology, and fisheries.