Understanding the Differences Between A-Run and B-Run Steelhead

Steelhead trout are a remarkable species, known for their migratory journey from freshwater rivers to the vast expanse of the ocean and back again. For anglers in Idaho, the two distinct types of ocean-run steelhead—A-run and B-run—are a fascinating subject of discussion. These two categories are defined by their differing life cycles, time spent in the ocean, and the resulting differences in size and behavior. Let’s explore what sets these two types of steelhead apart.

Life Cycle Differences

The primary distinction between A-run and B-run steelhead lies in the duration of their ocean phase. Both begin their lives in Idaho’s rivers, spending their first year or two in freshwater before embarking on their journey to the Pacific Ocean. Once they reach the ocean, their paths diverge:

• A-Run Steelhead: These fish typically spend about two years in the ocean before returning to Idaho’s rivers to spawn. Their shorter time spent in the ocean limits the time they have to feed and grow.
• B-Run Steelhead: In contrast, B-run steelhead spend approximately three years in the ocean before making their return. This additional year allows them to accumulate more resources and reach a larger size.

The timing of their migration also differs. A-run steelhead usually begin their upstream journey earlier in the season, while B-run steelhead tend to arrive later, often overlapping with the fall Chinook salmon run.

 

 

Size and Physical Differences

The most notable difference between A-run and B-run steelhead is their size. The extra year spent in the nutrient-rich waters of the Pacific Ocean provides B-run steelhead with a significant advantage in growth.

• A-Run Steelhead Size: These fish generally measure between 20 to 28 inches in length and weigh between 4 to 8 pounds. This is an average, but they can also be 30+ inches, and weigh 10+ pounds as well!
• B-Run Steelhead Size: B-run steelhead, with their additional ocean year, often reach lengths of 28 to 34 inches and can weigh 10 to 20 pounds or more. Their larger size not only makes them a prized catch for anglers but also equips them with greater strength and stamina to navigate challenging river conditions.

Behavioral and Habitat Preferences

The size difference between A-run and B-run steelhead influences their behavior and habitat preferences:

• A-Run Steelhead: These fish tend to favor smaller tributaries and rivers with moderate flow. Their smaller size and stature allows them to navigate narrower waterways with ease.
• B-Run Steelhead: Larger and more robust, B-run steelhead are better suited to larger rivers with stronger currents. 

Fishing Considerations

For anglers, understanding the differences between A-run and B-run steelhead can significantly enhance the fishing experience, and which river system to fish. Each type offers unique challenges and rewards:

• A-Run Steelhead: Their smaller size makes them a bit more predictable and accessible to novice anglers. They’re often found closer to the river’s mouth and in areas with moderate flow, making them easier to target with light tackle. 
• B-Run Steelhead: These giants demand more skill and preparation. Their size and strength require heavier gear and more strategic approaches. 

 

 

Conservation Concerns

These Steelhead populations face numerous challenges, including habitat degradation, damns, climate change, seals, and overfishing. Understanding the distinct needs and behaviors of A-run and B-run steelhead is crucial for effective conservation efforts. Protecting spawning grounds, improving fish passage at dams, or eliminating them altogether are all essential measures to ensure the survival of these iconic fish.

Final Thoughts

A-run and B-run steelhead are both remarkable species! Their differences in size, behavior, and habitat preferences highlight the incredible diversity within a single species. For anglers, these distinctions offer a chance to target two very different fishing experiences. 

Whether you’re chasing the smaller, agile A-run steelhead or the massive, powerful B-run, Idaho’s waters offer unparalleled opportunities to connect with one of these magnificent fish. Understanding their unique characteristics not only enhances the fishing experience but also deepens our appreciation for the journey they take.