In a large non-stick skillet over medium heat, soften the onion, celery, garlic and pepper in the oil. Add the potatoes, corn, tomatoes, tomato paste, cornstarch and cilantro. Bring to a boil and let simmer for 10 minutes. Add the salmon and continue cooking for 2 minutes. Add the shrimp. Season with salt and pepper and stir gently. Transfer to an 11 x 8-inch (28 x 20 cm) baking dish. Set aside.