Assessment of multiple stressors on the growth of larval green sturgeon Acipenser medirostris: implications for recruitment of early life‐history stages

Abstract

Early developmental stages of fishes are particularly sensitive to changes in environmental variables that affect physiological processes such as metabolism and growth. Both temperature and food availability have significant effects on the growth and survival of larval and juvenile fishes. As climate change and anthropogenic disturbances influence sensitive rearing environments of fishes it is unlikely that they will experience changes in temperature or food availability in isolation. Therefore, it is critical that we determine the effects of each of these potential stressors on larval growth and development, as well as understand the additive, synergistic or antagonistic effects of both. We reared threatened green sturgeon Acipenser medirostris (initial age ca. 32 days post hatch) at four temperatures (11, 13, 16 and 19°C) and two food availability rates (100% and 40% of optimal) to assess the effects of these stressors and their interactions on larval growth. We compared the overall size (fork length, total length and mass), growth rates (cm day−1 and g day−1) and relative condition factor of these larval and juvenile fish at 3 week intervals for up to 12 weeks. Our results indicated that temperature and food availability both had significant effects on growth and condition and that there was a significant interaction between the two. Fish reared with limited food availability exhibited similar patterns in growth rates to those reared with elevated food rates, but the effects of temperature were greatly attenuated when fish were food‐limited. Also, the effects of temperature on condition were reversed when fish were reared with restricted food, such that fish reared at 19°C exhibited the highest relative condition when fed optimally, but the lowest relative condition when food was limited. These data are critical for the development of relevant bioenergetics models, which are needed to link the survival of larval sturgeons with historic environmental regimes, pinpoint temperature ranges for optimal survival and help target future restoration sites that will be important for the recovery of sturgeon populations.

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, ).…”

“…Green sturgeon display ‘sweepstakes’ reproduction (Hedgecock & Pudovkin, ) and experience massive early life stage mortality, which is likely impacted by more environmental factors than the temperature and discharge parameters we analysed. Other important factors not considered in this analysis include food availability and predation (Poletto et al, , S. Baird personal communication), which could be indirectly impacted by other environmental variables such as water quality and substrate type. The optimal solution is to manage water temperatures up to the threshold for winter‐run, so errors in the threshold model could lead to errors in this optimization.…”

“…Winter‐run spawned in high‐elevation cold habitat, whereas green sturgeon spawned in the warm mainstem (Figure ; Fisher, ; Mora, Lindley, Erickson, & Klimley, ). The optimal rearing temperature for larval green sturgeon is 19°C, whereas survival of incubating winter‐run eggs begins to decrease above 12°C (Martin et al, ; Poletto et al, ). These differences in temperature tolerance between the two species lead us to classify green sturgeon as a ‘warm‐water species’ and winter‐run as a ‘cold‐water species’ for the purposes of this manuscript, although these are relative classifications that are specific to this system.…”

“…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.…”

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

“…In the upper river, captures of juvenile Green Sturgeon peak between May and June (Poytress et al 2015). It is believed that young of the year begin their downriver migration to the SSJ Delta at the onset of winter, as temperatures in the upper watershed drop below the thermal optima (15-19°C) for growth at this life stage (Mayfield and Cech 2004;Poletto et al 2018;Hamda et al 2019). Typically, the lower reaches of the Sacramento River and SSJ Delta are warmer in the winter months compared to upstream habitats and may result in accelerated growth.…”