Halve the avocado, stone it and remove the flesh from the skin with a tablespoon. 3⁄4 Finely dice the fruit flesh and mix with 2 tablespoons of lime juice. Cut the rest of the avocado into slices. Sprinkle with 1 tbsp lime juice to prevent them from turning brown.
Finely dice the shrimp and salmon, mix with the avocado cubes. Season with pepper. Fold in 1 tablespoon of oil.
Place a garnish ring or aluminium foil (approx. 9 cm Ø) folded several times to form a ring on each plate. Spread the tartar evenly in the ring and press down lightly. Carefully loosen and remove the ring with a knife.
Sprinkle the tartar with 1-2 tbsp. oil and add 1 blob of crème fraîche and 1 tsp. caviar. Sprinkle with pepper. Garnish with avocado slices, dill and lime wedges.