The spawning migration is a critical life stage for many fishes, demanding effective navigation, energy management, and risk avoidance strategies. This is particularly challenging for non-homing, semelparous species like the sea lamprey (Petromyzon marinus), which undertakes extensive riverine migrations fueled solely by endogenous energy reserves while facing novel predation threats. Understanding the behavioral mechanisms underlying this migration extends beyond the increasing our knowledge of the movement ecology and animal behavior. It is crucial for both controlling invasive populations in the Laurentian Great Lakes and conserving native populations elsewhere. This dissertation integrates fine scale acoustic telemetry, computational fluid dynamics (CFD) modeling, and field-based experimental manipulations to investigate how migrating sea lampreys respond to key environmental signals—hydrogeomorphology, hydrodynamic currents, and chemical risk cues—within a natural river system.First, we demonstrate that sea lampreys utilize persistent geomorphological features for navigation. Tracking revealed that migrants consistently follow river thalwegs (deepest channels), swimming near the substrate. This behavior conferred a mean energetic saving of 5.8% compared to near-surface swimming and likely enhances safety from shoreline predators. We propose a novel navigation mechanism, hydrostatic pressure-guided rheotaxis, facilitates this efficient and potentially safer movement strategy. Second, we provide field-based validation of energy optimization theory by examining swim tactics in varying currents. Sea lampreys adjusted their swim speed to maintain a relatively constant ground speed (mean 0.92 body lengths s-1), consistent with minimizing the cost of transport according to exponential models. Minor decreases in speed in deeper water suggest potential trade-offs with perceived risk. Third, we investigated responses to predation risk using conspecific alarm cues. Exposure induced structured changes in movement consistent with odor-guided rheotaxis, including a localized intensive search phase (reduced speed, increased tortuosity). Critically, when navigating the risk cue, lampreys prioritized immediate avoidance of the odor plume, splitting paths around the source, rather than selecting routes through deeper, putatively safer, habitat. Collectively, these studies reveal that sea lamprey migration is guided by a sophisticated integration of environmental signals, resulting in predictable, context-dependent movement patterns. This research enhances our mechanistic understanding of migration ecology and provides actionable insights for management and conservation, informing the placement of control or passage devices and the application of behavioral manipulation strategies by highlighting the importance of river morphology, flow dynamics, and sensory cue interpretation.
Read
