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Dredging is considered a major threat/impedance to anadromous fish migrating to spawning habitat. Due to the perceived threat caused by dredging, environmental windows that restrict dredge operations are enforced within many rivers along the east coast. However, it is generally unknown how anadromous fish react to encountering an active dredge during spawning migrations. Atlantic sturgeon (ATS) are an endangered, anadromous species along the Atlantic slope of North America. To determine if and how an active dredge may affect ATS spawning migration, a Vemco Positioning System array was deployed around an active hydraulic-cutterhead dredge that adult ATS must traverse to reach spawning habitat in the James River, VA. Telemetry data showed that all ATS that entered the study area survived. ATS that migrated upstream during dredge operations (N = 103) traversed the dredge area and continued upstream to spawning habitat. Many ATS made multiple trips through the study area during dredge operations. There was no noticeable difference in swim behavior regardless of whether the dredge was absent or working within the study area. We suggest that dredging in the lower James River does not create a barrier for adult ATS migrating to spawning habitat or cause adults to significantly modify swim behavior. This is the first study to utilize fine-scale telemetry data to describe how an organism moves in relation to an active dredge. This methodology could be used to describe dredge-sturgeon interactions on different life stages and in other locations and could be expanded to other aquatic organisms of concern. [ABSTRACT FROM AUTHOR]

1. Floodplains are a key habitat for foraging, spawning and as a nursery for many riverine fish species. The lower Volga floodplains (Russian Federation) are still relatively undisturbed, while in Europe and North America, about 90% of floodplains have effectively been lost. 2. We examined relationships between the extent and timing of the spring flood, lateral spawning movements of fish species and timing and duration of spawning in the floodplain by sampling during spring 2006 and 2007. 3. Only the spawning of rheophilic species, that released their eggs in the floodplain, coincided with the flood. In contrast, the timing of spawning by eurytopic and limnophilic species was unrelated to flooding. 4. For most fish species, we found no indication that the majority of spawners in the floodplain originated from the main river channel, with the exception of sabrefish Pelecus cultratus. 5. We postulate that in the vast Volga-Akhtuba floodplain, fish spawning stocks mainly originate from permanent floodplain waterbodies, whereas hydrological conditions are dominated by the river. Both the river and waterbodies on the floodplain may serve as sources for recolonisation after local extinction because of extreme environmental conditions, such as freezing or desiccation. [ABSTRACT FROM AUTHOR]

Anadromous fishes migrate to sea, apparently to take advantage of growing conditions, and return to fresh water to spawn. Migration is an energetically demanding part of the life cycle, and animals tend to evolve physiological and behavioral traits that suit the environmental conditions they experience during migration. We hypothesized that this premature migration is a consequence of the fish having to avoid stressful summer temperatures in order to access certain suitable areas for spawning in the fall. We tested this idea in sockeye salmon, Oncorhynchus nerka, by compiling data on the timing of migration and spawning and the freshwater temperature regime along the migration route in populations throughout the species North American range. The timing of migration varied among populations and was primarily related to temperature regime during migration and the timing of spawning. When temperatures were moderate, sockeye salmon tended to migrate to the vicinity of the spawning grounds about 1 month prior to spawning, regardless of the length of the freshwater migration. A long delay between migration and spawning seems to be an adaptation to avoid migration when temperatures are high. The results supported the hypotheses that the mean and variance of delay among populations from warm areas would be greater than those for populations from cold areas. At the southern end of the North American range of sockeye salmon, populations in Washington State and southern British Columbia experience higher water temperatures than other populations, and may also have evolved greater tolerance of warm water than northern populations. In summary, patterns of migratory timing among populations reflect both passage conditions and spawning time for adults.