PhD Thesis defense by José Luis Crespo Picazo at the VISAVET Centre of the Complutense University of Madrid

May 22^nd, 2024

The aim of this thesis is to apply epidemiological surveillance as a fundamental tool to learn about the occurrence of diseases and causes of death in a population in a given area, to monitor them over time and to propase control or mitigation strategies in management plans. In the case of the Valencian Community, as in many other regions at national and international level, a complete study of the pathologies and causes of death of sea turtles has not yet been carried out. This thesis is an ordered, systematic and complete study of the sea turtles that appeared in the Valencian Community during the eleven years covered by the study (2010-2020), mainly of the species Caretta caretta. By means of a detailed clinical evaluation and a complete post-mortem study, ali specimens caught accidentally and reported by local fishermen, as well as those found stranded, alive and dead, in a good state of preservation of the carcass, have been evaluated.

Of the 984 turtles registe red in the Valencian Community during the study period, 56.4% 555) of the cases could be fully evaluated, establishing the state of health, the cause of stranding, the cause of death if applicable, and characterizing the pathologies present. Based on this analysis, it was found that in 92% of cases, the rea son for admission to the recovery center or death was due to interaction with human activities. In particular, accidental capture by professional fishermen is the main threat to sea turtles in the Region of Valencia. Within the impact of fishing, a huge reduction in income from longline fishing was observed, representing only 1.8% of income from fishing, compared to 62.9% from trawling or 35.3% from trammel net fishing. These interactions showed a clear seasonal pattern, with higher bycatch of individuals in the months with lower water temperatures, coinciding with autumn and winter. However, individua Is affected by entanglement in marine debris were concentrated in the summer months.

The pathologies described are mainly those resulting from accidental capture, with gas embolism and decompression syndrome being the most common effect diagnosed in a greater number of specimens (45.5%), followed by changes caused by water aspiration (14.6%). In those animals that died as a result of decompression syndrome, increased free fluid in the coelomic cavity, the presence of gas at the cardiovascular level and the segmenta! pattern of congestion in the intestinal mucosa were described as the main macroscopic findings, whereas animals that died by drowning did not show a consistent pattern of lesions.
The information presented in this thesis includes the most relevant epidemiological aspects of the causes of pathology and mortality in sea turtles in the Valencian Community during the study period, and should serve as a basis for management actions, as well as useful information for future studies in the region, and in any other area where sea turtles occur.