Targeting river operations to the critical thermal window of fish incubation: Model and case study on Sacramento River winter‐run Chinook salmon

Abstract

Allocating reservoir flows to meet societal and ecosystem needs under increasing water demands and climatic variability presents challenges to resource managers. Often, rivers have been regulated to meet flow and temperature compliance points or mimic historical patterns. Because it is difficult to assess if this approach is efficient, process‐based models are being used to design river operations. This paper describes a model for fish incubation survival based on the premise that mortality from thermal stress occurs over a critical window (CW) of embryo development. A model for the embryo CW based on metabolic studies of development is combined with density‐dependent and background mortalities to describe salmonid survival from egg fertilization to fry detection downstream. The model is calibrated with a two‐decade dataset of Sacramento River winter‐run Chinook salmon egg‐to‐fry survival. The effects of temperature exposure over a range of CWs were explored. Based on statistical and biological support, two alternative CWs were identified for temperature control: the entire incubation period and a short duration window prior to hatching. Survival under different CW assumptions and temperature control operations were simulated with an internet‐accessible form of the model. The analysis indicated that under years of limited cold‐water resources, targeting water releases to the CW prior to hatching would yield the highest incubation survival.

Gastrulation and hatch as critical thermal windows for salmonid embryo development

“…While this mechanism was evident here, it was less significant than the effect of temperature during G, which accounted for two thirds of the mortality observed at H in Study B. This finding mirrors similar observations for zebrafish (Icoglu Aksakal & Ciltas, 2018; Hosseini et al, 2019; Uchida et al, 2018) and suggests that high temperatures during G give rise to embryonic damage and carryover effects that result in mortality at H. This finding adds to other models (e.g., Anderson et al, 2022; Martin et al, 2020) that suggest the thermal sensitivity of salmonid embryos is controlled by temperature mediated increase in oxygen demand exceeding supply. In combination with ours, these models demonstrate that mortality at H is influenced by the imbalance between oxygen supply and demand in high temperatures at this life stage and embryonic damage caused by pre‐hatch exposure to thermal stress.…”

“…Alternatively, the carryover effect could involve mutations during G that produce distinct effects on cell fates and morphogenesis (Solnica-Krezel et al, 1996) that reduce the activity of the hatching enzyme or the embryo's ability to escape the egg membrane at hatch (Icoglu Aksakal & Ciltas, 2018;Hosseini et al, 2019). While more work is required to understand the mechanisms of the carryover effect, this study demonstrates and models the effects of an additional critical thermal window of salmonid embryo development with implications for water management strategies seeking to cool incubating fish populations (Anderson et al, 2022;Del Rio et al, 2021;Hamor & Garside, 1976;Martin et al, 2020).…”

“…While embryos are particularly vulnerable to mortality caused by high temperatures, their responses to thermal perturbations changes substantially from fertilisation to hatch (Anderson, Beer, Israel, & Greene, 2022; Dahlke et al, 2020; Del Rio et al, 2021; Martin et al, 2020). Salmonid embryo development begins with rapid cellular cleavage (C) in which the newly fertilised egg, through multiple divisions, forms two layers of cells that cover the interior membrane of the egg.…”

“…To mitigate the impact of temperature elevation caused by impoundment on embryo survival, cold water resources can be released from reservoirs to sustain favourable downstream thermal conditions. In some cases, this action is demanded by endangered species protection to ensure water temperatures meet the environmental requirements of target species (Anderson et al, 2022). Often, these conservation flows are designed to provide consistent, favourable temperatures throughout embryo development.…”

Effect of surface hydraulics and salmon redd size on redd induced hyporheic exchange

“…For oxygen delivery and consumption, however, both water temperature and interstitial flow velocity are important during embryos' development stage (Martin et al, 2020). In managed rivers such as the Sacramento River, high levels of water discharge can more rapidly deplete cool water pools stored in dams and thus lead to elevated temperature exposure during the embryonic period (Anderson et al, 2022). As a result, our findings should be interpreted in combination with a biophysical model of oxygen supply and demand for developing embryos to fully comprehend the significance of discharge for embryo survival (Martin et al, 2020).…”