Mouth Gape of Facultative Ram Ventilating Sharks (Squalus acanthias) in Response to Increased Swim Speed

• Virginia Farley, Marine Science, University of Delaware

• Aaron Carlisle, , University of Delaware
• Jonathan Cohen, , University of Delaware

Unlike obligate ram ventilators, smooth dogfish (Squalus acanthias) utilize both buccal pumping and ram ventilation. This physiological flexibility allows them to adjust to increased swimming speeds, and therefore increased metabolism, through strategies such as widening mouth gape or increasing gill beat frequency. Investigating these responses is essential for understanding how smooth dogfish regulate oxygen intake and overall metabolic rate. In this study, we quantified how swimming speed influences mouth gape and evaluated its potential role in metabolic regulation. We used a swim tunnel respirometer to systematically increase water current speeds and measure the corresponding mouth gape angles using ImageJ. As swim speed increased, we hypothesized that mouth gape would also increase, allowing for a greater volume of water (and therefore more oxygen) to pass over the gills. Preliminary findings suggest that mouth gape initially increases with swimming speed, but beyond a certain threshold, gape begins to decrease. This suggests a trade-off between oxygen intake and the metabolic cost of increased drag, indicating an upper limit to the benefit of increased mouth gape for the smooth dogfish. These findings provide insight into the unique respiratory strategies of facultative ram ventilators and indicate that further research is needed to fully understand this concept. This information could be used to inform bio-logging sensor designs used in the field studies of shark physiology and metabolism.