Decoding fishery survival rates and use of space of smooth hounds (Mustelus mustelus and Mustelus punctulatus) and spiny dogfish (Squalus acanthias) with a sentinel acoustic array in the Northern Adriatic Sea

Sharks, rays and skates have been declining worldwide, particularly in heavily exploited basins such as the Mediterranean Sea. Overfishing and bycatch are the major reasons, taking advantage of these animals’ innately sensitive life-history characteristics. Various management measures have the capacity to reduce the impact of such threats but require ample scientific data. This study utilized acoustic telemetry tools to study fishing survival and use of space of commercially important demersal shark species (Mustelus mustelus, Mustelus punctulatus, and Squalus acanthias) in the northern Adriatic Sea. Tagged with the help of chartered fishing vessels, 46 out of 85 individuals were detected over a sentinel array of acoustic receivers. Evidence of tag detachment was found in at least two individuals. Those released in better health conditions were detected in higher proportions and had high (61-100%) estimated survival ratios. It took longer than the expected period of recovery time (2-14 days) to detect animals, especially for the more mobile S. acanthias. Differences in use of space between and within species were observed, with residency being higher for smooth hounds (M. mustelus and M. punctulatus), and adult M. mustelus visiting more stations than their juvenile counterparts. Site fidelity was evident in one M. mustelus female. Temperature and refuge from fishing activities are proposed as important drivers of shark movement, which has implications for local fishing regulations, though more research is needed before defining strategies such as MPAs.