Data and code from: Keeping pace: Migrating sea lampreys adjust swim speed in response to shifting water velocity to maintain a constant ground speed

Upstream migrating fish must balance energetic costs with environmental
and ecological constraints. Theoretical models predict that fish can
conserve energy by adjusting swim speed in response to changing water
velocity, but detailed field tests of these predictions remain rare. We
used fine-scale acoustic telemetry and hydrodynamic modeling to track
adult sea lamprey (Petromyzon marinus) migrating through a river and
evaluated how movement speeds varied with environmental conditions and
individual traits. Swim speed increased with faster water velocities,
while ground speed remained constant, supporting the hypothesis that
lampreys regulate swim effort to maintain a fixed migration pace. The
average ground speed aligned with a predicted optimum of ~1 body length
per second. Both swim and ground speeds declined slightly in deeper water,
suggesting a trade-off between movement efficiency and predator avoidance.
These findings provide field-based support for a theoretical model of
energy optimization and underscore how migratory fish adaptively adjust
behavior to local hydrodynamic conditions. Our results highlight the value
of using high-resolution tracking and environmental modeling to reveal
behavioral tactics that underlie efficient migration strategies.