Individual Based Modelling of Fish Migration in a 2-D River System: Model Description and Case Study

Area of Science:

• Aquatic ecology
• Conservation biology
• Computational modeling

Background:

• Diadromous fish in the Pacific Northwest face significant threats to their migratory routes, including habitat degradation, harvesting, and physical barriers.
• These stressors impede longitudinal connectivity, making it difficult to prioritize management strategies for anadromous salmon and trout.

Purpose of the Study:

• To introduce a multi-scale, hybrid mechanistic-probabilistic simulation model that connects migration corridor conditions to fish fitness.
• To demonstrate the model's application with a case study of adult salmon and steelhead in the Columbia River, considering variable stressors.

Main Methods:

• A behavioral decision tree governs individual fish interactions within the simulated environment.
• An energetic submodel calculates the hourly energetic costs associated with migration.
• The model simulates emergent properties such as passage time, energy expenditure, and survival rates.

Main Results:

• Initial energy density, experienced water temperatures, and thermoregulation behaviors were key factors influencing simulated fish fitness.
• The model provides insights that can guide the development of management interventions to enhance migration success.

Conclusions:

• This study presents novel methods and a 2D, spatially-explicit model for simulating fish migration within river systems.
• The developed model can evaluate the trade-offs between behavioral thermoregulation and population-level fitness, aiding conservation efforts.