Melt butter in a large pot over medium heat. Add onion, celery, carrots, and garlic. Cook until vegetables are softened, about 5 minutes.
Sprinkle flour, thyme, and fennel seeds over the vegetables and stir to combine. Cook for 2 minutes to remove the raw flour taste.
Pour in chicken broth, bay leaves, and add diced potatoes. Bring to a boil, then reduce heat and simmer until potatoes are tender, about 15 minutes.
Add salmon chunks and corn to the pot. Cook until salmon and corn are cooked through, about 5-8 minutes.