1.Segment oranges over small bowl, reserve ¼ cup juice.
2.Combine salmon, 1 tablespoon reserved juice and half the vinegar in medium bowl. Cover, refrigerate 10 minutes.
3.Meanwhile, using mandolin or V-slicer, slice fennel and celery thinly. Chop 1 tablespoon fennel tips, reserve.
4.Combine salmon mixture, orange segments, fennel, celery, fennel tips, watercress, remaining juice and remaining vinegar in large bowl.