Grate 1/4 teaspoon peel from lime and squeeze 1/2 teaspoon juice. Stir together sour cream, lime peel, lime juice, 1/4 teaspoon cumin, sugar and pepper in small bowl. Set Lime Sauce aside.
Rinse and pat dry salmon. Sprinkle flesh side with remaining 1/2 teaspoon cumin and salt. Heat oil in 10-inch nonstick skillet over medium-high heat. Add fillet, skin-side down, and cook 4 minutes. Carefully turn fillet. Continue cooking 2 to 3 minutes more or until fish flakes easily with fork (145°F).
Cut fillet into 2 pieces. Serve with Lime Sauce on top or on side of salmon.