Batoid locomotion: effects of speed on pectoral fin deformation in the little skate, Leucoraja erinacea

Abstract

Most batoids have a unique swimming mode in which thrust is generated by either oscillating or undulating expanded pectoral fins that form a disc. Only one previous study of the freshwater stingray has quantified three-dimensional motions of the wing, and no comparable data are available for marine batoid species that may differ considerably in their mode of locomotion. Here, we investigate threedimensional kinematics of the pectoral wing of the little skate, Leucoraja erinacea, swimming steadily at two speeds [1 and 2 body lengths (BL) s]. We measured the motion of nine points in three dimensions during wing oscillation and determined that there are significant differences in movement amplitude among wing locations, as well as significant differences as speed increases in body angle, wing beat frequency and speed of the traveling wave on the wing. In addition, we analyzed differences in wing curvature with swimming speed. At 1 BL s −1 , the pectoral wing is convex in shape during the downstroke along the medio-lateral fin midline, but at 2 BL s −1 the pectoral fin at this location cups into the flow, indicating active curvature control and fin stiffening. Wing kinematics of the little skate differed considerably from previous work on the freshwater stingray, which does not show active cupping of the whole fin on the downstroke.

New approaches for assessing squid fin motions: Coupling proper orthogonal decomposition with volumetric particle tracking velocimetry

“…In fishes, rowing fin strokes ( parallel to the direction of motion) and undulations (≥1 propulsive wave present) are often used for efficient swimming at low speeds because they provide higher thrust, greater stability and better maneuverability than flapping fin strokes ( perpendicular to the direction of motion or <1/2 propulsive wave present). At higher speeds, flapping motions are more prevalent because they can generate greater thrust via circulatory forces and are mechanically more efficient overall (Walker and Westneat, 2002;Di Santo and Kenaley, 2016;Di Santo et al, 2017). Therefore, the observed progression toward more flap-like fin motions at higher speeds is consistent with previous fish studies.…”

“…The complex fluid-structure interactions associated with these muscular hydrostatic systems pose unique challenges for researchers interested in studying the kinematics and hydrodynamics of fin motions in squid. Similar challenges emerge when investigating fluid-structure interactions in other complex highly deformable surfaces, such as fish fins and insect, bird and bat wings (Riskin et al, 2008;Lentink and Dickinson, 2009;Tangorra et al, 2010;Neveln et al, 2014;Crandell and Tobalske, 2015;Di Santo et al, 2017). To address this complexity, tools to identify spatial and temporal components of fin motions and to quantify 3D flows shed from the fins are needed.…”

Diel vertical migration and central place foraging in benthic predators

“…While foraging, skates have been observed using their crura to 'walk' along the sea bed and manoeuvre with precision to search for buried prey using their electroreceptive sense and only to resort to swimming as an escape response when alarmed (Lucifora andVassallo 2002, Koester andSpirito 2003). At high swimming speeds (around 2 body lengths/s) the energetic costs increase significantly (Di Santo et al 2017) and consequently sustained high speed swimming, as might be required for pelagic hunting, is unlikely. The lower energetic cost of 'walking', in comparison to even slower (1 BL/s) swimming explains why most observed movements along the bottom involve walking using crura rather than swimming using undulations of the pectoral fins (Macesic andKajiura 2010, Di Santo et al 2017).…”

The evolution of underwater flight: The redistribution of pectoral fin rays, in manta rays and their relatives (Myliobatidae)

“…In most skates and rays, the pectoral fins are used for both undulatory swimming and feeding (Mulvany & Motta, ). Undulatory swimming, in which multiple waves are simultaneously propagated along the pectoral fin margin, is a maneuverable gait that is mechanically efficient for hovering and swimming above the benthos at low speeds, but not for travelling long distances (Di Santo, Blevins, & Lauder, ; Rosenberger, ; Walker & Westneat, ; Webb, ). Undulatory pectoral fins are used in feeding to constrain prey items under the body by pectoral fin edges pressed against the substrate in a behavior called “tenting” (Wilga, Maia, Nauwelaerts, & Lauder, ; Wilga & Motta, ).…”

“…mechanically efficient for hovering and swimming above the benthos at low speeds, but not for travelling long distances (Di Santo, Blevins, & Lauder, 2017;Rosenberger, 2001;Walker & Westneat, 2000;Webb, 1994). Undulatory pectoral fins are used in feeding to constrain prey items under the body by pectoral fin edges pressed against the substrate in a behavior called "tenting" (Wilga, Maia, Nauwelaerts, & Lauder, 2012;Wilga & Motta, 1998).…”