Unraveling multipredator impacts in salmon-bearing rivers using quantitative DNA metabarcoding

Area of Science:

• Ecology
• Conservation Biology
• Aquatic Ecosystems

Background:

• Invasive species pose increasing threats to native ecosystems globally.
• Pacific salmon (Oncorhynchus spp.) smolts face significant predation during migration from both native and nonnative predators.
• Understanding complex trophic interactions is crucial for effective conservation and management strategies.

Purpose of the Study:

• To investigate the diets of co-occurring native and nonnative fish predators in Pacific Northwest rivers using DNA metabarcoding.
• To quantify the predation risk posed by these predators to Pacific salmon smolts, particularly Chinook salmon (Oncorhynchus tshawytscha).
• To assess the broader impacts on native prey species and identify potential compensatory effects in food webs.

Main Methods:

• Utilized quantitative DNA (qDNA) metabarcoding to analyze the gut contents of fish predators.
• Examined trophic interactions among native and nonnative fish assemblages in salmon-bearing rivers.
• Collected data over two years to capture spatiotemporal variations in predation patterns.

Main Results:

• Nonnative smallmouth bass (Micropterus dolomieu) frequently consumed Chinook salmon, which ranked as their second most important prey.
• Predation on Chinook salmon varied with environmental conditions (smolt abundance, discharge, temperature) and location.
• Native species, including lamprey and sculpin, were significant prey for nonnative predators, and intraguild predation was common.

Conclusions:

• Multispecies, spatiotemporal approaches are essential for understanding and managing invasive species impacts on salmon recovery.
• DNA metabarcoding is a valuable tool for elucidating complex food webs and identifying novel predator-prey relationships.
• Integrated management strategies considering intraguild predation are necessary to avoid compensatory effects and conserve biodiversity.