Understanding activity patterns of aquatic animals through acoustic telemetryapplication to the marine fish species Epinephelus marginatus (Lowe 1834)

Zusammenfassung

Ethology (or the study of animal behaviour) is a relatively old scientific discipline resulting from historical human interest in animals. Despite this, there are still many unanswered questions about animal behaviour, mainly due to the difficulty of obtaining data from animals over time. A few decades ago, the appearance of animal-borne devices that take data of different nature (temperature, position, depth, etc.) over time was a revolution in this respect. However, like all technologies, this technology is subject to dizzying technical improvements, which means that the type of data obtained is improved day by day, opening up new horizons in the study of animal behaviour. One of the behavioural traits that arouse most interest is that of activity patterns, as it allows us to infer, among other things, the type of interaction between species. In the aquatic environment, however, the study of activity, as with most behavioural traits, is severely constrained by both the limitations of technology and the difficulties of working in this environment. One of the leading technologies for studying aquatic animal behaviour is acoustic telemetry, based on the use of transmitters that emit information through acoustic waves and receivers (hydrophones) that receive it. Historically, this technology has been used to address various questions related to the activity patterns of aquatic animals. However, studies that have answered such questions have been based on assumptions that are not validated and difficult to test, such as, for example, the establishment of a linear relationship between activity and the number of detections. However, the relatively recent emergence of triaxial accelerometers is making it possible to overcome previously insurmountable barriers to knowledge. Accelerometers are sensors that measure acceleration and have been used for decades in mobile phones and other smart devices, allowing, among other things, to know the orientation of the object that incorporates it. Thanks to the close relationship between acceleration and energy expenditure in animals, accelerometers are becoming the main tool for inferring activity in animals, both terrestrial and marine. Despite this and the possibility of incorporating accelerometers into acoustic transmitters, some work still uses non-accelerometer derived data to infer activity. Therefore, the main objective of this thesis is to improve the understanding of activity patterns in aquatic animal species through acoustic telemetry. Chapter 1 proposes a method of synchronising independent electronic devices that record simultaneously over time, which is essential due to clock drift and the need to compare data from acoustic transmitters and accelerometers in Chapter 2. Chapter 2 evaluated the performance of various types of acoustic telemetry data as activity indicators, comparing them with acceleration data obtained simultaneously by independent accelerometers. Finally, in Chapter 3, we evaluated the effect of some environmental factors and recreational diving on the activity patterns of grouper (Epinephelus marginatus; Lowe 1834), using acceleration data and Hidden Markov Models (HMM). The results of this thesis contribute to a better interpretation of acoustic telemetry data for inferring activity and also provide novel approaches to address this issue of interest in the scientific literature.