Successful Pacific salmon reintroduction into rivers where they have been extirpated requires understanding the range of habitats and environmental conditions that currently exist and their ability to support target species. Chinook Salmon Oncorhynchus tshawytscha were extirpated from the San Joaquin River, California, over 60 years ago and are targeted for reintroduction into the system. To assess the remaining habitat along the longitudinal lower San Joaquin River gradient, juvenile Chinook Salmon were reared within an Alluvial Site, a Transitional Site, and two lowland sites (Lowland Cinnamon Slough and Lowland Eastside Bypass) during two rearing periods (early and late). The highest Chinook Salmon growth rates were observed during the early rearing period within the lowland sites when water temperatures were moderate and prey densities were greatest. However, high-water events precluded a spatial comparison of growth with that of fish reared at the Alluvial and Transitional sites during the early period. In the late rearing period, the lowest and highest growth rates were observed at the Lowland Eastside Bypass (lowest prey abundance) and Lowland Cinnamon Slough (highest prey abundance), respectively. Growth rates at the Alluvial and Transitional sites were intermediate between those at the two lowland sites. Main-channel (Alluvial and Transitional) growth rates were generally lower than those within the lowland sites, suggesting that main-channel restoration may require targeted food web enhancement. Our results indicate that lowland floodplain sites can provide quality rearing habitat and growth benefits early in the rearing season. As temperatures increase, salmon can continue to grow if sufficient prey is available. Managers considering measures for improving floodplain access to provide juvenile Chinook Salmon rearing habitat should consider interactions between environmental conditions and prey density-and how these factors vary along the river continuum-to determine when these habitats can provide the greatest growth benefit.
We performed a preliminary evaluation of a mobile sampling platform with adjustable push net and live box (Platform) against two common methods for sampling small-bodied fish (i.e., 10–100 mm) in two distinct lentic habitats. Nearshore (NS) littoral habitat was sampled by Platform and beach seine, and open water (OW) pelagic habitat by Platform and Kodiak trawl. Our goal was to evaluate the Platform’s ability to describe fish assemblage structure across habitat types in contrast to common techniques restricted to single habitat types that are less comparable due to gear-specific bias. Platform sample speed had a significant positive effect on recapture efficiency of both nearly neutrally buoyant objects and marked fish. Marked fish recapture efficiencies were similar for Platform in NS and OW, indicating similar efficiency across habitat types. Platform capture efficiency was similar to beach seine and greater than Kodiak trawl. With similar sampling time, the Platform collected more individuals and taxa in NS relative to beach seine and in OW relative to Kodiak trawl. Greater taxa detection by the Platform suggests that it may be effective at detecting species that are numerically rare in specific habitats when compared to these methods. Fish CPUE was significantly greater NS regardless of technique. However, by using the Platform, there is greater confidence that this difference was reliable and not a gear selectivity artifact. Overall, this preliminary study demonstrates the Platform’s potential to collect standardized data across NS and OW habitats, track ontogenetic habitat shifts, and detect differences in small-bodied fish taxa richness, relative abundance, and density between NS and OW habitats. Continued experimentation beyond a single reservoir and fish size range is required before consensus can be established regarding the utility of this new push net design.
Introduction of non-native piscivores has been implicated in the decline of native Chinook Salmon Oncorhynchus tshawytscha via predation during juvenile life stages. However, isolating effects of predation on Chinook Salmon survival is complicated by changes in physical habitat that are often concomitant with non-native piscivore establishment. We performed two field experiments with enclosures deployed in tidal freshwater habitat to quantify effects of non-native Largemouth Bass Micropterus salmoides density and habitat type on the survival and movement behavior of juvenile Chinook Salmon. In experiment one, bass densities were doubled and quadrupled across treatment levels with a baseline value of field-observed densities. In experiment two, three habitat types (dock, submerged aquatic vegetation (SAV), and open water) were tested while bass density was held at the medium (doubled) value. Juvenile Chinook Salmon implanted with passive integrated transponders were released into the enclosures to assess their survival and movement through the treatments over multiple trials. Mark-recapture models indicated that the survival of juvenile Chinook Salmon was reduced in the medium bass density, but not the highdensity treatment, when compared to the lowest density value suggesting relationships may be non-linear. The SAV treatment had a well-supported negative effect on juvenile Chinook Salmon survival relative to a dock or open water. Residence time was positively related to bass density. Relationships with a habitat were not consistently different. These results suggest that restoration strategies targeting non-native SAV control could reduce predation on juvenile Chinook Salmon by Largemouth Bass. However, piscivore density manipulation may only be effective over a narrow range of densities.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.