Network analyses reveal intra‐ and interspecific differences in behaviour when passing a complex migration obstacle

Abstract

Summary Network theory offers new perspective on movement data by evaluating the relationships between animal movements (links) and detection locations (nodes) in spatially complex systems, including human‐altered landscapes. We applied network analyses to intra‐ and interspecific movement patterns in the migration behaviour and dam passage success of two anadromous fish species, Pacific lamprey Entosphenus tridentatus Gairdner and Chinook salmon Oncorhynchus tshawytscha Walbaum, when moving through a large multifishway hydroelectric project (Bonneville Dam, USA). Network analyses revealed greater variation in movement for Pacific lamprey compared with Chinook salmon. Salmon that passed the dam had networks consisting of more direct passage routes with fewer overall movements compared with lamprey that passed the dam. Lamprey that did not pass the dam exhibited a wide range of behaviours, from approaching only one fishway site to testing all possible passage routes. Accounting for the time spent in the network improved the ability to detect biological differences in network structure for lamprey that did and did not pass the dam. The movement patterns likely resulted from different behavioural responses to complex environmental and internal factors affecting a philopatric species (Chinook salmon) vs. a non‐philopatric species (Pacific lamprey) when moving through an engineered environment designed primarily for salmon. Synthesis and applications. Our case study highlights the potential for network analyses to link questions of basic movement ecology with monitoring of movement and behaviour in human‐altered landscapes. Network analyses can thus serve as a valuable tool for describing movement and behaviour in the face of environmental change and assessing the effectiveness of mitigation efforts at spatially complex obstacles to animal movement.

Individual movement variation in upstream‐migrating sea lamprey Petromyzon marinus in a highly fragmented river

“…For example, passage probability may have decreased sharply if initial attempts to pass the barrier resulted in exhaustion in unsuccessful individuals. Unsuccessful attempts to pass also may have resulted in lamprey switching behavioural states (Gurarie et al., 2016) to search for alternative passage routes or spawning habitats (retreat) or adopt a sedentary sit‐and‐wait (for favourable passage conditions) strategy (Kirk & Caudill, 2017; Rooney et al., 2015). Although we show evidence of large‐scale exploratory behaviour, understanding these apparent sit‐and‐wait strategies requires finer‐scale telemetry/biologging studies to assess the behaviour of individuals that were delayed but remained in the immediate vicinity of migration barriers (Harbicht et al., 2018).…”

“…For example, at the first three weirs encountered by upstream-migrating lamprey, more than 30% of individuals made downstream (>1 km) movements, whereas others displayed a high degree of residency to the area immediately downstream of the barriers. This variation in movement tendency may reflect different strategies with respect to passage at barriers (Kirk & Caudill, 2017), with some individual lampreys searching for alternative routes and others awaiting favourable passage conditions. For example, the downstream extent of retreats from By testing the retreat rate data against abiotic data, we revealed that increased river discharge reduced retreat rates and the likelihood of exploratory behaviours, with this consistent with H2.…”

“…This can impact the fitness of migrating animals by preventing access to optimal reproductive or feeding sites, and/or incurring additional energetic costs as migrants attempt to overcome obstacles along their migratory path (Benoit et al., 2020; Castro‐Santos & Letcher, 2010; Nyqvist et al., 2017). The ability of individuals to overcome barriers, and hence the persistence of populations within fragmented ecosystems, can be determined by their phenotypic traits (e.g., physical and behavioural traits) and the barrier characteristics (e.g., head height) (Kirk & Caudill, 2017; Rolls et al., 2014). Population‐level diversity in migration phenology potentially can be reduced or disrupted by barriers, where passage by migrants relies on episodic environmental events which may be unpredictable/stochastic in nature (Zeigler & Fagan, 2014).…”

“…The ability of individuals to overcome barriers, and hence the persistence of populations within fragmented ecosystems, can be determined by their phenotypic traits (e.g., physical and behavioural traits) and the barrier characteristics (e.g., head height) (Kirk & Caudill, 2017;Rolls et al, 2014). Population-level diversity in migration phenology potentially can be reduced or disrupted by barriers, where passage by migrants relies on episodic environmental events which may be unpredictable/stochastic in nature (Zeigler & Fagan, 2014).…”

Selective fragmentation and the management of fish movement across anthropogenic barriers

“…Although we do not know much about the mechanisms causing differences in behavioral tendencies, behavioral differences could contribute to passage success or failure. Kirk and Caudill (2017) observed a wide range of behaviors in Pacific lampreys (Lampetra tridentate) at fishways in the Columbia River, Oregon, USA. Success at passing through the fishways was not related to body size but appeared related to behavioral differences as lampreys that failed to pass through the fishway made fewer entrance attempts and showed less milling behavior than lampreys that passed through the fishway.…”