Shrimp and Sausage Gumbo

Ingredients

1 1/2 pounds small (51-60 per pound) shrimp, peeled & deveined (shells & tails reserved)
1 cup clam juice
1/2 cup + 1 tablespoon vegetable oil, divided
1/2 cup all-purpose flour
2 medium onions, finely chopped
1 medium red bell pepper, finely chopped
1 rib celery, finely chopped
12 oz frozen sliced okra (sliced about 1/2 inch thick)
6 garlic cloves, minced
1 tablespoon fresh thyme, chopped
1/4 teaspoon cayenne pepper
2 bay leaves
1 pound andouille sausage, sliced 1/4 inch thick
1/2 cup chopped parsley
kosher salt & freshly ground black pepper, to taste
4 cups steamed brown rice, hot
4 scallions, thinly sliced