Abstract
Fine-scale space-use of drift-feeding fish is underpinned by an energetic trade-off that makes spatial positioning paramount for fitness, especially in a group context. However, methodologies used to study the space-use of drift-feeding fish are mainly based on direct visual observation, and the accuracy of such an approach can be questionable. Furthermore, previous studies mainly focused on the space-use of territorial salmonids, as they are relatively easy to observe. Here, we use a digital imaging technique to manually extract the spatial position of fish and feeding events in three dimensions (3D), at a very fine spatiotemporal scale, from in situ stereo-video footages. We use a motion model to quantify individual space-use strategies in two dimensions (2D) through the horizontal plane (perpendicular to gravity) and through the vertical plane (parallel to the flow). We study territorial (brown trout, Salmo trutta) and nonterritorial (roundhead galaxiid, Galaxias anomalus) juvenile drift-feeding fish to test this methodology over a broad spectrum of drift-feeding fish space-use. Results show that the methodology used permits the reliable quantification of space-use by territorial and nonterritorial drift-feeding fish and could be used to reveal relevant insights on their respective behavioral ecologies.