In a large saucepan over medium heat, melt the butter. Add the onion and celery and sprinkle with salt. Sauté until the vegetables are tender, about 5 minutes.
Add the onion and cook until fragrant, another minute. Stir in the chicken broth and the tomato paste and bring to a simmer, whisking to combine.
Place the cream cheese in a blender and add the hot broth mixture. Blend until smooth. Return to the saucepan and add the cream, salmon, and capers. Bring back to a simmer over medium low heat, to warm through.