Individual habitat use and behavior of acoustically-tagged juvenile green sturgeon in the Sacramento-San Joaquin Delta

Michael J Thomas,Eric D Chapman,Matthew L Peterson,A Peter Klimley,Nann A Fangue

doi:10.1007/s10641-019-00888-1

Michael J Thomas, Eric D Chapman + Show 3 more

Open Access

https://doi.org/10.1007/s10641-019-00888-1

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Abstract

Southern distinct population segment (sDPS) juvenile Green Sturgeon are thought to rear in the Sacramento-San Joaquin Delta for two to four years. The southern population segment has been listed as “threatened” under the Endangered Species Act. Habitat loss is cited as a significant driver in declines of the population. Specific to juvenile rearing, much of the historic floodplain habitat has been lost and replaced by leveed channelized waterways. In addition to geomorphic alterations, other direct and indirect activities such as water export, dredging, and the introduction of invasive species may have significant impacts to the viability of the species. The objective of this tracking study was to provide a first of its kind look at the movements and behaviors of wild caught juvenile Green Sturgeon within the putative nursery grounds of the Sacramento-San Joaquin Delta. We acoustically tagged and continuously tracked six yearling juvenile Green Sturgeon with mean total length (TL) of 50.6 cm (SD = 5.3) and mean mass of 563.3 g (SD = 151.7). We performed continuous mobile tracking for a period of up to five days per individual while recording GPS coordinates, depths, and water temperature at the sturgeon’s location. We used first-passage times, defined as the amount of time spent within a given area, for which a radius was determined post hoc. First passage times were used as a metric for parsing bouts of localized movements from directed movements. Our results indicate that juvenile Green Sturgeon largely oriented at or near the bottom. Depths utilized by all sturgeon ranged from >3 m to 20 m across all tracks. Individuals exhibited fidelity to the San Joaquin River Channel with only one individual leaving the main channel. Juvenile green sturgeon were shown to exhibit both positive and negative rheotaxis during sustained directed movements under independent ebb tidal cycles. This study provides the first detailed examination into the early life movements and behaviors of a rare species within their putative nursery grounds.

Highlights

The juvenile life stage is the least understood within the complex life cycle of the Green Sturgeon (Acipenser medirostris)
Our results indicate that juvenile Green Sturgeon largely oriented at or near the bottom
The general study location was based on information taken from Radtke (1966), who documented the seasonal presence of juvenile Green Sturgeon at Santa Clara Shoals (Fig. 1)

Summary

Introduction

The juvenile life stage is the least understood within the complex life cycle of the Green Sturgeon (Acipenser medirostris). Green Sturgeon are an anadromous fish species that spend the majority of their adult lives in the northeast Pacific Ocean along the western coast of North America (Lindley et al 2008; Moser et al 2016). They return to their natal waters approximately every two to four years to spawn (Erickson and Webb 2007). Juveniles may spend the two to three years rearing in the complex network of waterways known as the SSJ Delta and the San Francisco estuary (Moyle 2002)

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Conclusion