Residualization of Hatchery Steelhead: A Meta-Analysis of Hatchery Practices

North American Journal of Fisheries Management (Impact Factor: 1.18). 01/2012; 32:905-921. DOI: 10.1080/02755947.2012.711269

ABSTRACT Freshwater residualization, whereby anadromous juvenile salmonids fail to emigrate seawards within the primary migration period, causes considerable economic and ecological management concern. Previous studies have attempted to identify possible factors contributing to residualization, including both fish-related and release methodology-related attributes, in order to develop measures to reduce it. Here, we synthesize 48 previous estimates of the residualization rates of hatchery-reared steelhead Oncorhynchus mykiss from 16 studies and evaluate the cross-study effects of several factors that can be controlled by hatchery managers. The proportion of fish in hatchery release groups that residualized ranged from 0% to 17% (average, 5.6%). Characteristics of the release process were dominant in affecting residualization rates, while characteristics of individual steelhead primarily determined which, but not how many, individuals residualized. Releases of fewer fish and those located closer to the ocean or to a confluence with a major river produced fewer residuals than larger releases located further upstream. Acclimation ponds also appeared to reduce residualization, but there was no evidence of a release date effect across locations and years. Within a release year, individuals from endemic broodstock had higher residualization rates than those from hatchery-propagated broodstock while smaller individuals and larger males were more likely to residualize than individuals of intermediate size (similar to 213 mm fork length). To meet management objectives of reducing steelhead residualization, we recommend releases closer to an ocean or large river, particularly for releases of relatively few fish, in conjunction with the use of acclimation ponds. Management effort should focus on selective harvesting of hatchery residuals, a process which may be supported by rearing and release strategies. These objectives may trade off with conservation objectives; straying risk and genetic effects should especially be taken into account.

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    ABSTRACT: Drawing on acoustic telemetry this study identifies and describes local and regional scale survival and movement patterns of Central California Coast steelhead (Oncorhynchus mykiss), including their potential utilization of newly restored tidal marsh habitats in the Napa River system. Between April 8th and May 5th of 2010, 20 steelhead smolts ranging in fork length from 164 to 305 mm were collected, tagged with acoustic transmitters, and released in the upper Napa River (above tidal influence). We found no effect of release date (P < 0.001) or size (P < 0.005) on survival estimates based on model likelihoods. Cumulative survival from smolt release location to the Golden Gate Bridge over approximately 77 river kilometers (RKM) was 0.60 (SE = 0.16). Reach-specific survival was lowest in the initial 30 km reach (0.70 SE = 0.1). Survival was higher in San Pablo Bay (0.89 SE = 0.1) and San Francisco Bay (0.96 SE = 0.2). Sixty percent of the fish that entered the ocean were detected on a line of acoustic monitors at Point Reyes approximately 60 km north of the Golden Gate. Average movement rates of smolts were highest in San Pablo Bay (36.6 km∙d-1 SE = 3.3) and San Francisco Bay (28.9 km∙d-1 SE = 6.6). Smolts migrated more slowly in the river (9.0 km∙d-1 SE = 0.9) and ocean (4.1 km∙d-1 SE = 1.2). However, smolt movement rates in the river were dependent on location. Average movement rates of smolts were greatest shortly before their exit from the Napa River (83 km∙d-1 SE = 13.2). Fish were not detected within the recently reconnected former salt production ponds (North, Central, and South units) adjacent to the Napa River. Based on the detection patterns of fish throughout the study area, it appears that most fish were moving at relatively high rates and were not exploring off-channel habitat.
    Environmental Biology of Fishes 96(2-3). · 1.31 Impact Factor


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May 30, 2014