Turning performance and wake dynamics of neritic squids

Turning is important for ecological success in the oceans. It is essential for capturing prey, escaping predators, and navigating complex environments. Although squids are central to food web dynamics, little is known quantitatively about their turning dynamics. To assess turning capacity of neritic squids, quantify the role of propulsors and orientation in turning, and determine if jet flow is predictive of performance, kinematic and 3D velocimetry data were collected from the longfin squid Doryteuthis pealeii and shortfin squid Illex illecebrosus and combined with a subset of data from a prior study of brief squid Lolliguncula brevis. All animals were captured in Maine (43.8 degrees N, 69.6 degrees W) and Virginia (37.6 degrees N, 75.7 degrees W) waters. Experiments were conducted in July-October 2018 and 2019. Lolliguncula brevis was the most proficient at turning, with the highest mean and maximum angular velocity (O-mean, O-max) and the lowest minimum length-specific turning radius (R/L-min). Relative to the fins, the pulsed jet contributed to a greater percentage of impulse magnitude and angular impulse (71-72%) during turns in all squids. Arms-first turns, which were powered by short jets, were associated with lower mean and minimum length-specific turning radii (R/L-mean, R/L-min) than tail-first turns. Greater O-mean and O-max were achieved during tail-first turns for L. brevis and I. illecebrosus and arms-first turns for D. pealeii, with jet velocity/impulse being the primary factor contributing to these differences. While the jet was the main driver of turns, no one jet property predicted performance across the squids, with jet length-to-diameter ratio, velocity, and frequency all playing roles.

Automated summary

Turning plays a crucial role in ecological success in the oceans, allowing squids to capture prey, escape predators, and navigate complex environments. However, there is limited quantitative knowledge about their turning dynamics. This study examined the turning capacity of neritic squids, focusing on the role of propulsors and orientation, and investigated if jet flow can predict their performance. The results showed that Lolliguncula brevis was the most proficient at turning, with the highest angular velocity and the lowest turning radius. The pulsed jet was found to contribute significantly to turns in all squids, and the direction of the turns and jet velocity/impulse were key factors affecting turning performance.