Kinematics and muscle activity during punting in freshwater stingrays.
Many, benthic batoids (skates and rays) locomote by use of the water's substrate (Wilga and Lauder, 2004, Macesic and Kajiura, 2010). They perform what is known as augmented punting in which the thrust from pelvic fins are assisted by oscillations of the pectoral fins (Macesic and Kajiura 2010). The goal of my thesis is to better understand gait transitions, or changes in movement patterns while transitioning from one speed to another (Vogel, 2003a), in freshwater stingray punting. Specifically, I want to know how pectoral fins and the pelvic fins contribute to increasing punting speeds. I used five freshwater stingrays (Potamotrygon hystrix), and tested them each in a flume, recording electromyography (EMG) and video kinematics while speeds were increased. Nested ANOVAs were performed for both EMG and kinematic data. I found that none of the variables for each muscle change significantly with speed. For kinematics, the normalized pectoral fin amplitude significantly change with increased speed, but pectoral fin wave frequency (Hz) and punt frequency (Hz) do not significantly increase with increasing speeds. Previous research indicates that in stingray swimming, pectoral frequency increases and pectoral fin amplitude remains constant across different speeds (Blevins and Lauder, 2012; Rosenberger and Westnest, 1999). These differences suggest that punting and swimming undergo different kinematic strategies which may help reduce the cost of energy for each mode of locomotion.
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