RAPID: The effects of wildfire on salmonid olfaction and behavior

Olfaction, the sense of smell, is critical for aquatic animals to sense their surroundings. Toxic compounds in the environment may interfere with this ability. Wildfire has become a dominant feature of Western landscapes.

When forests burn, they can release toxic heavy metals, which ultimately end up in streams. These compounds may interfere with the ability of animals to smell their surroundings, thereby changing behavior. This research examines the effects of recent California wildfires on the olfaction and behavior of Pacific salmon.

Salmon use their sense of smell to detect predators. If this ability is disrupted, they may quickly become a predator’s lunch. Salmon also use smell to find their way back to their home streams to reproduce after years at sea.

This process, called olfactory imprinting, is a specialized form of learning that juvenile salmon experience in streams. If this imprinting is disrupted, they are unable to find their way back to their home stream as adults. This research uses behavioral experiments to test whether fish from fire-impacted streams are less able to smell predators.

It uses behavioral experiments and cellular studies of olfactory function to test whether fish from fire-impacted streams are less able to recognize and imprint on their home watersheds. This project will train students, broaden participation in science, advance a general understanding of the effects of sensory pollutants on wild populations, and contribute critical information to inform salmon management in a drier, more fire-prone landscape.

In aquatic environments, olfactory cues provide important information that animals use to make behavioral decisions. Wildfires may cause large-scale disturbance to aquatic chemical environments that may impact olfaction and behavior at the scale of entire ecosystems. Fires release organic and inorganic compounds into streams.

Some of these compounds, including heavy metals, may disrupt olfaction and alter behavior. This proposed research combines behavioral experiments with gene expression assays to ask: How does wildfire impact juvenile salmonid olfaction and behavior in natural streams? Recent wildfires that occurred in August 2020 along the Central California Coast have generated a mosaic of burned and unburned watersheds.

This project uses a paired sampling design, pairing burned and unburned streams within four watersheds. Spatially isolated sites within each watershed have been selected to ensure juvenile salmonids cannot move between the burned and unburned sites. This project will measure the concentrations of heavy metals in stream water and in fish muscle tissue from burned and unburned streams within each watershed.

The behavior of juvenile salmonids from burned and unburned streams will be compared in terms of predator avoidance and recognition of natal stream water. The expression of genes associated with normal olfactory function and natal homing will be compared between fish from burned versus unburned streams. If the release of heavy metals by fire disrupts juvenile salmonid olfaction, then fish from burned streams are expected to exhibit weaker predator avoidance, impaired recognition of natal stream water, and reduced expression of genes associated with olfactory imprinting.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.