Strandings of loggerhead sea turtles south of the Po River delta: insights from a highly impacted area

Abstract

The northern Adriatic Sea is an important foraging ground for the loggerhead sea turtle Caretta caretta (Linnaeus, 1758) within the Mediterranean Sea. Here, spatial-temporal patterns of loggerhead sea turtles strandings along a short portion ([~]18 km) of the coast south of the Po River delta (Italy) during a three-year period (2019-2021) were investigated. A total of 244 records (alive, n=7; dead, n=237) were analysed and the curved carapace lengths (CCL, notch to tip, cm) mainly reflected sub-adults (average CCL=55.2 cm; 95% CI= 53.3-57). The month of July was identified as the critical month with the highest number of strandings, mirroring migratory processes toward this area during warmer months. Interaction with the trawl fishery was hypothesized as the main cause of mortality and a small fraction of deaths (6%; n=16) could be linked to boat strikes and net entanglement. The number of stranded turtles*km-1 as well as the absolute number of strandings along the short portion of monitored coast confirmed this area as the most impacted in Italy and perhaps in the whole Mediterranean Sea. This study provides valuable information to improve conservation efforts for this species and highlight that, with all due caution, monitoring stranding events can offer useful insights into the geographic ranges, seasonal distribution, and life history of marine species of conservation interest such as the loggerhead sea turtle.