1. In a big skillet, melt the butter over medium heat.
2. Saute the onion, celery, and mushrooms for about 7 minutes or until the mushrooms have given off their liquid and start to brown.
3. In a 4-quart slow cooker add the sauteed vegetables and potatoes; stir to combine.
4. Add in the clam juice, water, wine, tarragon, thyme, and pepper.
5. Cover and cook on LOW for 6-7 hours or until the potatoes are tender.
6. In a bowl, add the cornstarch and cream; whisk to combine; add into the chowder; stir to combine.
7. Add in the salmon and peas; increase heat to HIGH; cover and cook about 15 minutes or until the salmon is firm.
8. Add salt to taste.
9. Ladle chowder into individual soup bowls; sprinkle with parsley or chives.