Identification of upper thermal thresholds during development in the endangered Nechako white sturgeon with management implications for a regulated river

Abstract

Climate change-induced warming effects are already evident in river ecosystems, and projected increases in temperature will continue to amplify stress on fish communities. In addition, many rivers globally are impacted by dams, which have many negative effects on fishes by altering flow, blocking fish passage, and changing sediment composition. However, in some systems, dams present an opportunity to manage river temperature through regulated releases of cooler water. For example, there is a government mandate for Kenney dam operators in the Nechako river, British Columbia, Canada, to maintain river temperature <20°C in July and August to protect migrating sockeye salmon (Oncorhynchus nerka). However, there is another endangered fish species inhabiting the same river, Nechako white sturgeon (Acipenser transmontanus), and it is unclear if these current temperature regulations, or timing of the regulations, are suitable for spawning and developing sturgeon. In this study, we aimed to identify upper thermal thresholds in white sturgeon embryos and larvae to investigate if exposure to current river temperatures are playing a role in recruitment failure. We incubated embryos and yolk-sac larvae in three environmentally relevant temperatures (14, 18 and 21°C) throughout development to identify thermal thresholds across different levels of biological organization. Our results demonstrate upper thermal thresholds at 21°C across physiological measurements in embryo and yolk-sac larvae white sturgeon. Before hatch, both embryo survival and metabolic rate were reduced at 21°C. After hatch, sublethal consequences continued at 21°C because larval sturgeon had decreased thermal plasticity and a dampened transcriptional response during development. In recent years, the Nechako river has reached 21°C by the end of June, and at this temperature, a decrease in sturgeon performance is evident in most of the traits measured. As such, the thermal thresholds identified here suggest current temperature regulations may not be suitable for developing white sturgeon and future recruitment.

Thermal exposure risk in different life stages of Chinook salmon in the Nechako River system, British Columbia

“…Evidence from this study reinforces the need to revisit and enhance the STMP to ensure the long-term viability of the Nechako River species (Earhart et al, 2023;M. A. Oyinlola et al, 2023).…”

Physiological responses to acute warming at the agitation temperature in a temperate shark

“…However, it is not clear whether a Hif1α response could occur with warming above the agitation temperature. In various fishes, hif1α transcript abundance has been shown to increase at CT max (Earhart et al, 2023;O'Brien et al, 2020); although, links between Hif1α and CT max are equivocal (Joyce and Perry, 2020). Cellular stress may be connected to the neuroendocrine stress response; however, S. suckleyi has been shown not to exhibit a catecholaminergic response to acute warming but only up to 16°C (Sandblom et al, 2009).…”

Heatwave resilience of juvenile white sturgeon is associated with epigenetic and transcriptional alterations

“…Although the observed differences in CTmax between pre-heatwave and heatwave fish could, in principle, be due to the 20 days between these two measurements, it is much more likely that this increase in thermal tolerance is due to thermal acclimation associated with the heatwave exposure. Not only is it well documented across fish species that warm acclimation increases thermal tolerance 8 , 39 , this response to thermal acclimation has also been reported in the same population of sturgeon at different ages 28 , 40 , 41 . Increases in CTmax following various thermal acclimation temperatures are demonstrated across white sturgeon populations 42 , 43 and other sturgeon species 26 , 28 , 40 , 43 – 46 .…”

“…Not only is it well documented across fish species that warm acclimation increases thermal tolerance 8 , 39 , this response to thermal acclimation has also been reported in the same population of sturgeon at different ages 28 , 40 , 41 . Increases in CTmax following various thermal acclimation temperatures are demonstrated across white sturgeon populations 42 , 43 and other sturgeon species 26 , 28 , 40 , 43 – 46 . In fact, sturgeon have higher capacity for acclimation, measured as the acclimation response ratio (ARR), and show unusual plasticity and resilience to rapidly increasing temperatures compared to other fishes 39 , 47 .…”

“…In fact, sturgeon have higher capacity for acclimation, measured as the acclimation response ratio (ARR), and show unusual plasticity and resilience to rapidly increasing temperatures compared to other fishes 39 , 47 . Further, this acclimation capacity is even more pronounced in early developmental stages, where white sturgeon at the yolk-sac larvae stage have an ARR of over 1 40 . In this study, juvenile sturgeon exhibited an ARR of 0.55, which is higher than average for a temperate fish species 39 , but similar to that of slightly older white sturgeon 28 indicating that white sturgeon have substantial capacity for plasticity and are remarkably tolerant to temperature changes.…”