1. Using a large chef's knife, peel the oranges or grapefruit and the tangerines. Working with 1 fruit at a time, slice off both ends. Stand the fruit on one end, then slice downward, following the curve of the fruit, cutting away both the skin and pith, but leaving as much of the fruit as possible. Using a paring knife and working over a bowl to catch the juices, cut between the segments to detach each piece from its surrounding membrane. You will need 12 segments of both orange and tangerine. Set the segments aside; squeeze the empty membranes and reserve the juice.

2. Halve the fennel bulbs lengthwise. Using a mandoline or vegetable peeler, thinly slice the fennel. Set aside.

3. In a large skillet over medium heat, heat the 1 tablespoon grapeseed or olive oil. Add the fennel to the pan, being careful not to crowd the skillet (cook in batches if necessary). Cook for 3 to 4 minutes. Turn and cook for 3 to 4 minutes longer, until evenly softened. Transfer to a plate lined with a paper towel to drain. Cover to keep warm.

4. In a small bowl, whisk together any reserved juice from the oranges and tangerines with the lemon juice, 1/3 cup olive oil and ground fennel seeds. Season with salt and pepper to taste.

5. To serve, in a large bowl, gently toss the mache with the vinaigrette. Place the fennel in the center of individual plates. Divide the mache mixture evenly among the plates and place 2 segments of orange and 2 segments of tangerine on top. Arrange the salmon on top and drizzle any remaining vinaigrette on top. Garnish, if desired, with fennel fronds. Serve at once.