Climate Warming Effects on Chinook Salmon Foraging Conditions and Growth

This project collected data to run foraging and bioenergetics models that simulate how flow and temperature affect growth. We invented two sampling devices, a suction pump to sample drifting prey and a computer vision system to measure the inedible debris that occupy most of a fish’s feeding effort. We combined our data with USGS and NOAA records to predict temperature, turbidity, prey, and debris on a daily basis throughout our study years (2019-2020) and others.



Our model results suggest that juvenile Chinook Salmon growth in the Chena River is primarily controlled by temperature early and by food intake later in the summer. Food intake depended strongly on both prey availability and the concentration of debris particles that vastly outnumber prey, distracting fish and making prey detection difficult. Individual high-flow events were predicted to reduce foraging success, despite moderately increasing prey availability, because they dramatically increased the ratio of debris to prey. These events suppressed growth by reducing foraging success and temperature.



We evaluated climate change scenarios including increases of water temperature by 2, 4, and 8 °C. Our models suggest the river would be resilient to changes in temperature alone, because the warming high-quality but currently too-cold habitats upstream would offset the loss of downstream habitats to excessive warming. However, if climate change increases the frequency and severity of high-flow events as predicted, the decline in foraging conditions in the mainstem during high-flow events would pose a serious problem. Still-water sloughs provide valuable refugia during high flows, and preserving connectivity to these habitats is a worthy priority for restoration.



This project utilized funds from PCSRF grant NA16NMF4380336; no funds from this grant were used past its end date.

This project will clarify the intertwined roles of temperature, streamflow, and prey availability in controlling juvenile Chinook salmon growth, habitat needs, and climate vulnerability. Managers can use such information to prioritize the type and location of restoration actions that will provide refugia from challenging conditions and reinforce strongholds of juvenile Chinook salmon in the Chena River. The spatiotemporal variability in juvenile Chinook salmon foraging conditions is important both for assessing habitat quality and for anticipating consequences of environmental change because prey consumption determines whether growth rates will respond positively or negatively to a warming climate, or to restoration of relatively warm-water habitats. Sampling spatially diverse sites will also help determine whether the relatively warm, developed, lower reaches of the Chena River basin comprise potential high-quality habitat in need of restoration, or whether patterns in foraging conditions limit prey consumption to a degree that makes warmer water less suitable for growth than currently heavily occupied habitats. Given that high freshwater growth rates are beneficial to the long-term survival of Yukon Chinook, and freshwater streamflow is strongly related to population productivity, the information this project provides will help managers optimize restoration of the freshwater environment to conserve future Chinook salmon returns.