Fish farms, parasites, and predators: implications for salmon population dynamics

Area of Science:

• Ecology
• Aquatic Biology
• Parasitology

Background:

• Sea lice (Lepeophtheirus salmonis) from salmon farms impact wild salmon populations.
• Predation is a major source of mortality for juvenile salmon.

Purpose of the Study:

• To investigate how sea lice infestation affects predation risk and mortality in juvenile pink and chum salmon.
• To develop a mathematical model for assessing sea lice impacts on salmon population dynamics and conservation.

Main Methods:

• Risk-taking, schooling, and prey selection experiments were conducted with infected and uninfected juvenile salmon.
• Predation experiments involved cutthroat trout and coho salmon as predators.
• A mathematical model incorporating a type II functional response was developed.

Main Results:

• Infected juvenile salmon exhibited increased risk-taking behavior and altered school positions.
• Predators selectively consumed infected salmon, indicating reduced evasion ability.
• Sea lice increase predator attack rates but not handling time.

Conclusions:

• Sea lice significantly increase juvenile salmon mortality through enhanced predation.
• Predation dynamics can mask the true impact of sea lice on salmon populations.
• Findings are critical for accurate mortality estimation, infection control, and conservation policy development.