Temperature, discharge and development shape the larval diets of threatened green sturgeon in a highly managed section of the Sacramento River

Abstract

Feeding at early fish life stages is a key determinant of survival to recruitment. To understand the environmental and developmental determinants of early life stage feeding in ESA-threatened green sturgeon (Acipenser medirostris), we performed a diet study in a highly managed section of California's Sacramento River, where temperature and discharge are controlled by dam releases. Utilising field collections from 2012 to 2016, we assessed the impacts of temperature, discharge and morphological development on the composition and number of prey items in larval green sturgeon diets. Results show that there are more empty stomachs at colder temperatures.Higher discharge conditions decreased prey taxon richness and counts, especially the abundance of cyclopoid copepods in diets. Fish smaller than 30 mm had teeth on the oral jaws and showed a strong reliance on zooplankton prey. The developmental loss of teeth in fish greater than 30 mm was associated with decreased zooplankton consumption and increased richness of benthic macroinvertebrates in diets. Our results show that river management through dam releases has the potential to impact the earliest life stage of green sturgeon by reducing the prevalence of favoured zooplankton prey in diets.

Managing hydropower dam releases for water users and imperiled fishes with contrasting thermal habitat requirements

“…By introducing larval green sturgeon condition to a winter‐run egg survival model in multi‐object optimization, we identify a Pareto frontier with a corner that is optimal for both species. Our study corroborates others which found that indices of health in larval green sturgeon are enhanced at higher temperatures (Hamda et al, ; Mayfield & Cech, ; Poletto et al, ; Zarri & Palkovacs, ), but body condition appears to be more sensitive to changes in discharge at the range of environmental variables experienced in our study region (Figure a). Furthermore, the positive correlation of green sturgeon body condition with temperature may be moderated by food availability, as fish exposed to warm temperatures with low food availability show very low body condition (Poletto et al, ).…”

“…These two objectives are of primary importance for Shasta Dam releases but likely harm ESA‐threatened green sturgeon, which depend on warm low flow conditions to support larval growth. High discharge has a strong impact on developing green sturgeon larvae swimming ability and is associated with decreased prey richness and diet count (Verhille et al, ; Zarri & Palkovacs, ). By introducing larval green sturgeon condition to a winter‐run egg survival model in multi‐object optimization, we identify a Pareto frontier with a corner that is optimal for both species.…”

“…Cold‐water pollution below dams dramatically impacts mainstem ecosystems that are adapted for warmer temperatures (Astles, Winstanley, Harris, & Gehrke, ). Larval green sturgeon growth, food consumption, food conversion efficiency and diet indices are positively influenced by warmer temperatures (Mayfield & Cech, ; Poletto et al, ; Zarri & Palkovacs, ), suggesting that cold releases for winter‐run may negatively impact green sturgeon.…”

Aquatic insects differentially affect lake sturgeon larval phenotypes and egg surface microbial communities

“…Accordingly, conditions encountered by offspring during incubation, and maternal effects are important to growth and survival [ 98 ]. The period where larvae shift from endogenous reserves to exogenous feeding is particularly critical for survival [ 13 , 99 ], due to the risk of predation and starvation at these early life stages [ 100 ]. Both sources of mortality have been tied to body size.…”

Influence of the size and form of Artemia sp. nauplii on the growth and survival of Atlantic sturgeon (Acipenser oxyrinchus Mitchill) larvae

“…nauplii feed on the growth and survival of larval... mechanism of ingesting feed in sturgeons depends on the species. The mouths of predatory sturgeons open to the front, while those of benthic feeding sturgeons are directed downward (Zarri and Palkovacs 2019). However, this type of feeding limits maximum prey size and is not effective for catching large or highly mobile prey (Miller 2004).…”