Analysis of Sea Turtle Bycatch by Andalusia Pelagic Longline Fleet in the Northeast Atlantic

The Northeast Atlantic is one of the most crucial foraging grounds for juvenile loggerhead ( Caretta caretta ) and leatherback turtles ( Dermochelys coriacea ), while also serving as an important fishing area for the Andalusia surface longline fishery. The main aim of present study is to assess the sea turtle interaction with the Andalusia pelagic longline fleet operating in the Northeast Atlantic. Between 2004 and 2023, a total of 235 sea turtles were observed incidentally caught during longline fishing operations in 975,379 hooks. These records correspond to data collected by the onboard observer program of the Spanish Institute of Oceanography (IEO), which covered 4.82% of total fishing activity in the area. Loggerhead turtles ( n = 218) and leatherbacks ( n = 17) were the only turtle species caught, with catch rates of 0.251 and 0.017 turtles per 1000 hooks, respectively. A generalized linear mixed model (GLMM) with negative binomial distribution revealed that season and moon phase significantly influenced catch per unit effort (CPUE), with spring ( p = 0.024) being associated with fewer incidental captures and new moon ( p = 0.035) with higher captures. Additionally, increased distance from the coast was positively correlated with higher CPUE ( p = 0.006), while latitude exhibited a negative relationship with CPUE ( p = 0.020). These findings contribute to our understanding of the variables involved in the incidental capture of sea turtles in surface longline fisheries targeting swordfish around the Canary Islands and may support the development of improved management strategies for their conservation.