The ocean has depth: two- versus three-dimensional space use estimators in a demersal reef fish

Abstract

Most aquatic animals employ 3-dimensional (3D) movements to fully exploit the resources of the environment they inhabit. Many of these animals, however, are impossible to observe directly, making it necessary to use indirect methods of observation such as biotelemetry in order to study them. Despite technological advances with tracking equipment enabling movement to be assessed in 3 dimensions, many studies restrict their analyses to traditional 2-dimensional (2D) space use. We compared 2D and 3D (1) core and home range size, (2) home range overlap and (3) changes in space use in relation to biological and environmental variables of a large, demersal reef-dwelling fish species, the eastern blue groper Achoerodus viridis, tracked using passive acoustic telemetry. Mixed effects models were used to determine differences between the core/home range sizes and home range overlap between the sex of the fish and the breeding and non-breeding seasons. The 2D analyses were unable to detect differences in core and home range sizes between the sexes that were successfully identified by the 3D analyses. 2D analyses only detected differences in home range overlap between the breeding and non-breeding seasons, whereas the 3D analyses found seasonal differences according to the sex of the fish. Two-hourly 2D space use estimates failed to detect differences in space use between fished and protected areas that were detected in the 3D analyses. This study demonstrates that to truly understand how animals use the space they inhabit, we must assess their movement in the full spatial context of their environment.

Modelling the three‐dimensional space use of aquatic animals combining topography and Eulerian telemetry data

“…In accordance with previous works based on 3D approaches (e.g. Vivancos et al, ; Lee et al, ), our results corroborate that 2D estimations overestimate the spatial overlap because they do not account for the segregation of individuals across depth, and therefore, they provide a partial and biased view of individual behavioural processes. In comparison with other 3D‐UD estimation methods, our method redistributes the UD according to the topography and provides spatially explicit space use estimations.…”

“…aggregations, avoidances) are often reflected in a vertical stratification of the space use (Simpfendorfer, Olsen, Heupel, & Moland, 2012;Vivancos, Closs, & Tentelier, 2016). In marine environments, movement analyses that are limited to the 2D space provide a partial if not unrealistic view of the underpinning biological processes, and 3D approaches are required to obtain relevant ecological and behavioural conclusions (Belant et al, 2012;Lee, Huveneers, Duong, & Harcourt, 2017).…”

Animal-Borne Telemetry: An Integral Component of the Ocean Observing Toolkit

“…Integration of multiple data streams, such as environmental variables, to help interpret movements and space-use, also enhance the value of telemetry data but present new analytical and data management challenges (see below). Finally, technological advances, including sensors integrated into transmitters, provide another layer of data complexity, while concomitantly providing an opportunity to develop a refined sense of movement in three dimensions (Simpfendorfer et al, 2012;Udyawer et al, 2015;Lee et al, 2017).…”

Optimizing marine spatial plans with animal tracking data

“…For some animals, especially most aquatic species, the home range is three-dimensional ( Fig. 1; Lee et al 2017). Individual home range is influenced by a variety of factors, including habitat quality, prey availability, and shelter from predators (Speed et al 2010).…”

“…The appropriate technology for characterizing animal distributions depends largely upon the animal (e.g., its size, morphology, anatomy, behaviours, physiology, natural history) and the environment in which it lives. Tracking data enables advanced estimation methods that can account for resource selection (Wilson et al 2018) and depth use (Ballard et al 2012;Lee et al 2017) to calculate distribution. Acoustic tags require a tagged individual to move within the range of a compatible receiver and therefore cannot be used to accurately calculate the range of many vagile species (Heupel et al 2006).…”