Stranding of Spawning Run Green Sturgeon in the Sacramento River: Post‐Rescue Movements and Potential Population‐Level Effects

Abstract

The lower portion of the Sacramento River, California, has been highly engineered to protect low‐lying surrounding communities from annual flood events. While engineered floodplains have provided adequate protection for the surrounding communities, there remain unintended consequences to migratory fish that become stranded during high flow events. In April 2011, we rescued 24 threatened Green Sturgeon Acipenser medirostris that were stranded in two flood diversions along the Sacramento River. We tagged these 24 Green Sturgeon with acoustic tags and analyzed their survival and migration success to their spawning grounds. Additionally, we provided a population viability analysis to show the potential impacts of stranding and the benefits of conducting rescues at the population level. We found that 17 of these 24 individuals continued their upstream migration to the spawning grounds. Modeling suggests that recurrent stranding of a similar magnitude without rescue could affect the long‐term viability of Green Sturgeon in the Sacramento River. Population viability analyses of rescue predicted a 7% decrease below the population baseline model over 50 years as opposed to 33% without rescue. Despite the mitigated impact to the population with rescue, fish passage improvements should be considered as a long‐term goal for preventing population risks at flood control diversions.Received May 4, 2012; accepted December 6, 2012

Natural stranding of Atlantic sturgeon (Acipenser oxyrinchus Mitchill, 1815) in Scot's Bay, Bay of Fundy, Nova Scotia, from populations of concern in the United States and Canada

“…Implications of sturgeon stranding events on population abundance have been investigated for green sturgeon populations in California, U. S. (Thomas et al., ). It was determined that an individual stranding event was not likely to have an effect at the population level, although reoccurring events at times of low abundance might (Thomas et al., ). As the Saint John River and Kennebec River populations of Atlantic sturgeon consist of several hundreds to thousands of adults, this single stranding event would likely have little consequence at the population level.…”

“…For sturgeons, these stranding events may be natural (Parauka et al, 2011), or anthropogenic (Thomas et al, 2013). Most records of sturgeon stranding events occur in river systems, due to either natural seasonal water level changes, or changes caused by dams and flood diversions (Thomas et al, 2013). In 2004, Hurricane Ivan caused the stranding of Gulf Sturgeon in the Escambia River, Florida and nearby bays (Parauka et al, 2011).…”

“…The Atlantic sturgeon spawning population in the Kennebec River has not been calculated, however, more than 570 fish have been captured and marked in recent years, indicating that the total population exceeds this number (Stokesbury, Stokesbury, Balazik, & Dadswell, 2014). Implications of sturgeon stranding events on population abundance have been investigated for green sturgeon populations in California, U. S. (Thomas et al, 2013). It was determined that an individual stranding event was not likely to have an effect at the population level, although reoccurring events at times of low abundance might (Thomas et al, 2013).…”

“…Stranding is a component of natural mortality for fishes and has been reported for several species of sturgeon including Gulf sturgeon (Acipenser oxyrinchus desotoi; Parauka, Duncan, & Lang, 2011) and green sturgeon (Acipenser medirostris; Thomas et al, 2013). Stranding has not been documented for Atlantic sturgeon (A. oxyrinchus).…”

Real-time nodes permit adaptive management of endangered species of fishes

“…The sturgeon were trapped when the flows in the Sacramento River subsided, consequently lowering the height of the river below the crest of the weirs. A total of 24 green sturgeon were captured, transported, and released into the Sacramento River above the weirs [11].…”