Photogrammetric determination of movement speed of invasive Indo-Pacific lionfish in the Florida Keys.

Abstract

As a key determinant of how efficiently lionfish (Pterois sp.) locate and capture prey, swimming speed plays a crucial role in shaping the predator-prey interactions and broader ecological dynamics within the invaded ecosystems. Swimming speed on a small temporal and spatial scale is difficult to measure because of the need for precise measurements of both distance and duration of the behavior. Using photogrammetry by way of stereo-camera setups is ideal for analyzing the minutiae of lionfish behaviors because it can include the benefits of remote video traps coupled with precise measurements of movements in three-dimensional space and time. The primary objective of this study was to identify and characterize lionfish behavior associated with different movement speeds, and then to quantify small-scale swimming speeds of lionfish associated with those behaviors. Swimming speeds were classified under three different observed behaviors: relaxed swimming, traverse swimming, and striking at prey. The differences between these behaviors were primarily distinguished based on body and fin positioning, as well as the apparent intent of the motion if any was evident. The mean lionfish swimming speed from stereoscopic camera footage was 44.75 mm s^-1 for relaxed swimming, 138.99 mm s^-1 for traverse swimming, and 625.44 mm s^-1 for striking at prey. Swimming speed can be used to quantify how much habitat area a lionfish may cover in a day, and therefore the amount of prey that may be encountered by a predator. Lionfish feeding success under different environmental conditions could be an important factor in understanding their survival and growth in areas where they are found.