Low summer river flows associated with low productivity of Chinook salmon in a watershed with shifting hydrology

Abstract

Climate change and human activities are transforming river flows globally, with potentially large consequences for freshwater life. To help inform watershed and flow management, there is a need for empirical studies linking flows and fish productivity. We tested the effects of river conditions and other factors on 22 years of Chinook salmon productivity in a watershed in British Columbia, Canada. Freshwater conditions during adult salmon migration and spawning, as well as during juvenile rearing, explained a large amount of variation in productivity. August river flows while salmon fry reared had the strongest effect on productivity—our model predicted that cohorts that experience 50% below average flow in the August of rearing have 21% lower productivity. These contemporary relationships are set within long‐term changes in climate, land use, and hydrology. Over the last century, average August river discharge decreased by 26%, air temperatures warmed, and water withdrawals increased. Seventeen percent of the watershed was logged in the last 20 years. Our results suggest that, in order to remain stable, this Chinook salmon population being assessed for legal protection requires substantially higher August flow than previously recommended. Changing flow regimes—driven by watershed impacts and climate change—can threaten imperilled fish populations.

Adult spawners: A critical period for subarctic Chinook salmon in a changing climate

“…In that study, 30% of female and male fish held at 10°C died before reaching spawning grounds while 90% of females and 45% of males held at 18°C died before reaching spawning grounds (Crossin et al, 2008). Our findings align with recent studies indicating that Chinook salmon productivity declines with warm water temperatures and low summer river flows for populations in south central Alaska (Jones et al, 2020) and British Columbia (Warkentin et al, 2022).…”

Elevated temperatures reduce population-specific transcriptional plasticity in developing lake sturgeon (Acipenser fulvescens)

“…Greater than 50% of the world’s river basins face widespread anthropogenic impacts which limit productivity, species richness, and biodiversity, threatening approximately a quarter of freshwater fish species globally such as the lake sturgeon, Acipenser fulvescens (Palmer et al, 2008; IUCN, 2018; Grill et al, 2019; Su et al, 2021; Warkentin et al, 2022). Lake sturgeon are widely distributed throughout North America, and within Canada have experienced population declines >90% in the northern extent of their range since the 1960’s (COSEWIC, 2006).…”

Diversity in freshwater life history in spring and summer Chinook Salmon from the Fraser River, Canada

“…For yearling migrant populations that spawn in the Fraser River, the largest salmon‐producing river on Canada's Pacific coast (Northcote and Larkin 1989), this decline has been widespread and nearly all populations have been assessed as threatened or endangered by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC 2018). Analyses of the causes of decline have been conducted, with declining survival in the ocean (Welch et al 2021), land use modifications (e.g., deforestation, urbanization, and agriculture causing changes to freshwater habitat and flow), climate change (Warkentin et al 2022), and geological events (landslides) being identified as the most important threats (Riddell et al 2013; DFO 2020). However, planning for mitigation measures, such as changes to land and water management, invasive species control, habitat restoration, or hatchery supplementation (Chalifour et al 2022), is hampered by a limited understanding of freshwater life history and habitat use for this population group (Birtwell et al 1988; DFO 2020).…”