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Marine Ecology Progress Series

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MEPS 676:37-56 (2021)  -  DOI:

Otolith-based approaches indicate strong effects of environmental variation on growth of a Critically Endangered estuarine fish

Levi S. Lewis1,*, Christian Denney1, Malte Willmes1,2, Wilson Xieu1, Rachel A. Fichman1, Feng Zhao1, Bruce G. Hammock3, Andrew Schultz4, Nann Fangue1, James A. Hobbs1,5

1Wildlife, Fish and Conservation Biology, University of California, Davis, 1 Shields Ave, Davis, CA 95616, USA
2Institute of Marine Sciences/NOAA Fisheries Collaborative Program, University of California, Santa Cruz, 156 High Street, Santa Cruz, CA 95064, USA
3Cell Biology, School of Veterinary Medicine, University of California, 1089 Veterinary Medicine Drive, VetMed 3B, Davis, CA 95616, USA
4US Bureau of Reclamation Bay-Delta Office, Science Division, 980 9th St., Sacramento, CA 95814, USA
5California Department of Fish and Wildlife, 2109Arch Airport Road, Suite 100, Stockton, CA 95206, USA
*Corresponding author:

ABSTRACT: In estuaries, fluctuating environmental conditions exact strenuous physiological demands on the fishes that inhabit these oft-impacted areas, including the Critically Endangered delta smelt Hypomesus transpacificus in California (USA). Using an archive of otoliths spanning 2011-2019, we examined how growth rates of wild subadult delta smelt vary ontogenetically, regionally, and in relation to variation in the physical environment during late-summer and fall in the upper San Francisco Estuary. Recent growth rates were quantified using otolith increment analysis and modeled as functions of both intrinsic (age) and extrinsic (temperature, salinity, clarity, and region) factors using a suite of generalized additive models. Age explained 60% of the variation in log10-transformed growth rates, which peaked at 50-80 d post hatch. Overall, age-adjusted growth rates declined at temperatures >20°C, increased with practical salinity values of 0-4, and exhibited interactive patterns with water clarity. Growth rates appeared highest in the West and Central Delta, and lowest in the North Delta, also corresponding with patterns in environmental conditions. Here, we provide new evidence for how vital rates of wild delta smelt vary spatially and in relation to abiotic environmental variation. Such otolith-based growth reconstructions often provide the first direct look at how the vital rates of wild fish respond to environmental variation in situ, and how future changes are likely to affect the dynamics of wild populations.

KEY WORDS: Delta smelt · Hypomesus transpacificus · Water quality · Climate · Salinity · Temperature · Turbidity · Generalized additive model · Biological intercept

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Cite this article as: Lewis LS, Denney C, Willmes M, Xieu W and others (2021) Otolith-based approaches indicate strong effects of environmental variation on growth of a Critically Endangered estuarine fish. Mar Ecol Prog Ser 676:37-56.

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