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Abstract

Sand lances (Ammodytes spp.) rely on rapid burrowing into sediment for predator avoidance. Although their sediment grain-size preferences are well documented, the biomechanics underlying burrowing success remain unclear because natural substrates are opaque. Using a transparent-sediment system, we directly visualized and quantified burrowing kinematics to: (1) test the effect of body size (total length, TL) on burrowing success; (2) examine entry mechanisms (e.g., swimming speed, entry angle); and (3) describe locomotion within sediment. Logistic regression on the full dataset (N = 28 fish) identified TL as the primary determinant of success, with larger individuals exhibiting significantly higher success rates (p < 0.01). A secondary analysis of kinematic variables (N = 36 trials) found no significant predictors of success (all p > 0.05), suggesting that size-related physical capacity dominates over variation in entry technique. Within the sediment, fish employed serpentine locomotion described by sinusoidal waveforms. Waveform parameters (amplitude, wavenumber) were unrelated to TL (p > 0.15), indicating a conserved, size-independent movement pattern. This study provides the first direct quantitative analysis of sand lance subterranean biomechanics and identifies body size as a key constraint on burrowing performance and habitat use.

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