Wonders of Harbor and Grey Seal Whiskers: Morphology, Natural Frequencies, and 3D Modeling.

Seals can track fish using highly sensitive whiskers; however, the extent to which their morphologically diverse whiskers respond to hydrodynamic signals across frequencies remains unexplored. To address this, the lengths, thicknesses, curvatures, and natural frequencies of whisker arrays in grey seals (Halichoerus grypus) and harbor seals (Phoca vitulina) are measured. These values are mapped to their corresponding locations on the seal muzzle, and spatial trends (rostral-caudal and ventral-dorsal) are analyzed. These findings show that over 50% of whiskers exhibit underwater natural frequencies exceeding 80 Hz, which overlap with hydrodynamic fish trail frequencies (>100 Hz), demonstrating the adaptation of seal whiskers to hydrodynamic signals. Additionally, an open-access database of 141 full-length 3D whisker models is established. A streamlined method based on Euler spirals is proposed to fit and map seal whiskers simultaneously. This method evaluates the curvature of the full-length seal whisker and calculates morphological parameters (e.g., whisker axis and cross-sectional orientation angles) that are required for 3D whisker construction. The database of 3D seal whiskers offers a valuable resource for researchers in computational fluid dynamics, experimental biology, and sensor technology, supporting multidisciplinary studies of seal whiskers.