Speed-dependent locomotor patterns during steady swimming in a demersal shark.

Abstract

Swimming ability is critical for navigating complex benthic habitats, yet the biomechanical strategies demersal sharks employ to modulate body and fin movements across varying speeds remain largely unexplored. This study examines speed-dependent kinematic patterns in the small-spotted catshark (Scyliorhinus canicula), a benthic species with limited endurance for sustained swimming. Using high-speed videography in a flow tank, we quantified adjustments in tail beat frequency, body angle, wave speed and curvature across a range of speeds (0.5-6 body lengths per second). Our results reveal that S. canicula exhibits distinct kinematic shifts as speed increases, adopting a more streamlined posture and increasing tail beat frequency to accommodate higher flow rates. Principal component analysis identified swimming speed as the primary factor influencing kinematic variation, with higher speeds necessitating more consistent body alignment and tail movement. Strouhal numbers within the optimal range for propulsive efficiency (0.2-0.4) at intermediate speeds (1-2 BL s^-1) suggest that S. canicula maximizes energetic efficiency within this range, although further research is required to elucidate the metabolic implications. This study establishes a foundational framework for understanding the biomechanics of steady swimming in a demersal shark, providing insights into the ecological and evolutionary pressures shaping locomotor adaptations in benthic species.