# Refining Electronic Tagging of Marine Animals: Computational Fluid Dynamics and Pelagic Sharks

## TL;DR

This study uses simulations to show how attaching electronic tags to sharks affects their swimming and energy use, offering guidelines to reduce harm and improve research data.

## Contribution

The study introduces size-based tagging guidelines and optimal tag placement for sharks using computational fluid dynamics simulations.

## Key findings

- Tags on shark fins increased drag by up to 30%, making swimming more energy-intensive.
- Tags on the body caused minimal drag for sharks over 1.5 m but still increased energy use by 7% in smaller sharks.
- Optimal tagging practices are recommended to minimize drag and energy costs for tagged sharks.

## Abstract

Scientists commonly attach electronic tags to marine animals to study their movements and behavior in the ocean. However, these tags may have consequences by making it harder for animals to swim efficiently, potentially harming their recovery and survival while also affecting the quality of research data collected. This study used water flow simulations to understand how different types of tags and attachment locations affect the swimming ability of mako sharks of various sizes. The research tested multiple swimming speeds and tag configurations to measure changes in water resistance, which makes swimming more energy intensive. Results demonstrated that tags attached to fins significantly increased drag up to ~30%, making swimming more demanding. Tags attached to the main body performed better, causing minimal problems for larger sharks over 1.5 m long, but still created notable issues for smaller sharks, requiring about 7% more daily energy. Based on these findings, researchers recommend size-based limits for tagging and provide specific guidelines for optimal tag placement. This work helps scientists make better decisions about animal tagging practices, ensuring research can continue while minimizing harm to marine wildlife and maintaining reliable scientific data.

Animal-borne tags are widely used for tracking and monitoring the movements, behaviour, and ecology of marine animals. Tagging can, however, adversely affect the hydrodynamic force balance and welfare of tagged animals, and consequently, the reliability and accuracy of data, such as by increasing drag, altering swimming characteristics, and reducing the survival rate of tagged animals. Therefore, it is important to understand and quantify the impact of tagging on marine animal hydrodynamics and to optimize the choice of tag and attachment position. In this study, computational fluid dynamics (CFD) modelling is used to simulate the flow around tagged and untagged mako sharks (Lamnidae) across their swim speed range for two dominant tag shapes, tagging sites, and body sizes. The results indicate that fin mounted tags can have a significant impact on shark hydrodynamics and energetic balance, increasing drag between 17.6% and 31.2% for a mako shark (2.95 m fork length) across the range of flow velocities tested (0.5 to 9.1 m/s). In comparison, the optimal tagging site for archival tags attached to the dorsal musculature leads to a minimal increase in drag for the larger sharks (>1.5 m), which becomes considerable for small sharks (1 m fork length; 5.1% to 7.6% increase) and leads to an average energetic cost equivalent to 7% of the daily energetic requirement of an untagged animal. Other aspects of the force balance are considered, which reveal a range of varied and complex effects. Recommendations for animal size thresholds (>1.5 m FL) and refinements of tagging practice are suggested.