Network Analyses Reveal Differences in the Behaviors of Pacific Lamprey and Chinook Salmon at a Complex Migration Barrier

Behavioral differences between Pacific lamprey and Pacific salmonids are likely to be important for explaining why lamprey have lower success passing large hydropower dams. Network analyses provide a novel perspective for quantifying differences in behavior by evaluating the relationships between movement (links) and detection locations (nodes) in spatially complex environments. We used network analyses to test hypotheses about differences in the migration behaviors between Pacific lamprey and Chinook salmon at a large, multi-fishway hydropower dam (Bonneville Dam, Washington-Oregon, USA).  Network analyses revealed greater variation in network structure for Pacific lamprey compared with Chinook salmon, which also associated with dam passage success between the two species. Salmon that passed the dam had networks consisting of relatively direct passage routes, whereas lamprey that did and did not pass the dam exhibited a wider range of movements, from approaching only one fishway site to visiting every fishway location. These movement patterns were consistent with expectations based on differences in motivation for a philopatric species (Chinook salmon) versus a non-philopatric species (Pacific lamprey), and network analyses provided a new quantitative and comparative approach for evaluating those differences. More broadly, the analysis framework holds further potential for testing mechanistic hypotheses with complex movement data.