Analysis of Shark Fluid Dynamics to Guide Satellite Telemetry Tag Development

Abstract

Abstract Sharks are powerful predators that make long-range migrations across vast swaths of the ocean. Scientists attach satellite telemetry tracking tags to sharks in order to gather data on behavior, movement patterns and habitat usage. However, hydro-dynamic loading from these tags may unintentionally influence the host shark’s behavior, although the extent of the loading is still not well understood. While tag manufacturers have made incremental improvements to make tags lighter and smaller, there is still not a clear understanding between tag design and host animal impacts. This fundamental knowledge gap makes the design of telemetry tags difficult when aiming to minimize hydrodynamic effects. In this paper, we present an approach intended to help inform tag design. In addition, a case study demonstrates this approach using 3D digital models discussed in the introduction. Four different shark species: the great hammerhead (Sphyrna mokarran), shortfin mako (Isurus oxyrinchus), blacktip reef (Carcharhinus limbatus), and Caribbean reef (Carcharhinus perezii). We used computational fluid dynamics (CFD) methods to estimate baseline drag and lift coefficients from a range of angles of attack to simulate the sharks ascending, descending, and swimming horizontally. We solved lift and drag coefficients through force reports integrated into the CFD software, STAR-CCM+. The simulations were solved with the Menter shear stress transport (SST) k-ω turbulence model at steady-state. Across species, the drag and lift coefficients ranged from 0.14 – 0.21 and −0.02 – 0.37, respectively. To visualize the fluid dynamics, we created plots of pressure distribution and fluid flow associated with each shark’s average cruising speeds, providing insight for future researchers investigating optimal tag placement that minimizes the tag’s impact. To validate the computational models, we performed wind tunnel testing by using 3D printed models of each shark, allowing us to empirically measure lift and drag forces. A three-axis sting-balance style measurement system with strain gauges was used, while considering wind speed, fluid density, and matched Reynolds numbers associated with the CFD models for each species. Finally, we statistically compared the computational and wind tunnel measurements. Moving forward, we will explore the changes in drag and lift with different satellite tag models attached to the shark species. Our findings will support development of a methodology to quantify the hydrodynamic impact of different tag designs on sharks. This can be used by future researchers to determine the lift and drag forces a shark experiences with a satellite telemetry tag attached. Ultimately, this information will help to better monitor sharks in their natural environment and provide information that can be useful to the conservation of the species.