Experimental Quantification of Piscivore Density and Habitat Effects on Survival of Juvenile Chinook Salmon in a Tidal F
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Experimental Quantification of Piscivore Density and Habitat Effects on Survival of Juvenile Chinook Salmon in a Tidal Freshwater Estuary Steven C. Zeug 1 & Michael Beakes 1,2 & Jesse Wiesenfeld 1 & Marin Greenwood 3 & Lenny Grimaldo 4 & Jason Hassrick 5 & Alison Collins 6 & Shawn Acuña 6 & Myfanwy Johnston 1 Received: 4 May 2020 / Revised: 8 September 2020 / Accepted: 9 September 2020 # Coastal and Estuarine Research Federation 2020
Abstract 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. Keywords Predation . Mark-recapture . Predator control . California . Enclosures . Telemetry
Communicated by Mark S. Peterson * Steven C. Zeug [email protected] 1
Cramer Fish Sciences, 13300 New Airport Road, Suite 103, Auburn, CA 95602, USA
2
United States Bureau of Reclamation, 801 I Street, Suite 140, Sacramento, CA 95814, USA
3
ICF, 980 9th Street Suite 1200, Sacramento, CA 95814, USA
4
California Department of Water Resources, 1416 9th Street, Sacramento, CA 95814, USA
5
ICF, 201 Mission Street, 15th Floor, San Francisco, CA 94105, USA
6
The Metropolitan Water District of Southern California, 1121 L St #900, Sacramento, CA 95814, USA
Introduction Estuaries provide critical habitat for anadromous salmonids as they migrate between riverine and marine environments. Thes
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