Energy Harvesting From Aquatic Animals and Device Attachment Strategies Toward Long‐Term Tracking and Sensing Underwater

The advancement and miniaturization of tracking devices have deepened our understanding of aquatic ecosystems, including how human activities affect underwater animals and their habitats. However, long‐term or life‐cycle monitoring remains a major challenge because conventional animal‐borne devices rely on batteries with limited lifespans. As a sustainable alternative, researchers have introduced self‐powered tags and sensors that harvest electrical energy directly from the aquatic animal to power device operation. In this review, we examine energy‐harvesting methods used in animal‐borne devices in aquatic environments, including piezoelectric and triboelectric mechanisms, as well as thermoelectric, electrochemical, hydrokinetic, and electromechanical harvesting using ionic polymer–metal composites. Additionally, we briefly discuss energy storage options. Equally important, and inherently coupled to harvester design, is the development of durable attachment methods that minimize impacts on host‐animal welfare. Because the attachment governs how effectively the animal's motion couples to the harvester, while the harvester's form factor constrains viable attachment strategies, these two enablers must be co‐designed as an integrated system. We examine comprehensive attachment strategies spanning both internal (implantable) and external (wearable) applications, discussing surface‐based and nonsurface‐based adhesion methods that use diverse materials and designs. We also propose an example co‐design decision framework that maps species constraints such as morphology and swimming behavior to compatible attachment and harvester combinations. Lastly, we outline remaining challenges and suggest future research directions to enable long‐term, unobtrusive tracking and monitoring of aquatic animals in their natural habitats.