Bake the potatoes until tender, about 40 minutes. Let cool, then scoop out the flesh. Pass through a sieve or ricer. Mix with the eggs, fish, butter, chives, parsley, and pepper. Shape into small patties and dredge in the bread crumbs. Fry the sturgeon cakes in batches, 3 minutes on each side, until browned. They may be held in a 300 degree F oven.
For the Garnish: Mix the sour cream and chives together. Serve a dollop on the side of the fish cakes, sprinkled with sumakh and topped with sevruga.