Put the potatoes in a pot and cover with cold water; season with salt. Bring to a boil and cook until tender, about 20 minutes; drain and return to the pot. Stir in the butter, 1/2 tablespoon chives, and salt and pepper to taste; cover to keep warm.
Rinse the salmon under cold water; pat dry. Brush with 1 tablespoon olive oil and season with 1/2 teaspoon each salt and pepper. Heat 1 tablespoon olive oil in a large nonstick skillet over medium-high heat. Add the salmon, skin-side down; cook, shaking the skillet occasionally, until the skin is crisp, 5 minutes. Flip the salmon; continue cooking, flipping occasionally and sprinkling with the coriander and the remaining chives, until just opaque, about 7 more minutes. Remove from the skillet.
Add the remaining 1 tablespoon olive oil, the cabbage and tarragon to the skillet. Cook over medium-high heat, stirring, until the cabbage is wilted, 3 minutes. Season with salt and pepper. Serve the salmon with the cabbage and potatoes.