Heat oil in a large saucepan over medium heat. Add shallots, saffron, fennel seeds, and garlic to pan; cook 4 minutes or until tender. Add clam juice, Pernod, and tomato paste; bring to a boil. Reduce heat, and simmer 15 minutes.
Stir in tarragon, salt, pepper, potatoes, and fennel bulb; cover and cook 10 minutes. Add clams; cover and cook 10 minutes. Stir in shrimp. Cover and cook 2 minutes or until clams open and shrimp are done; discard any unopened shells.