Shovellers taste exactly like any other duck - when shot in the rice fields of NorCal. Did you shoot yours near salt water? If so, then what those guys said may be right. Spoonies near swamps can be REAL fishy-tasting.
But if they were in cornfields or inland or over rice, eat it. It will be yummy.
If you are worried and want to test it, try this: Take some fat from the bird and fry it in a pan on medium heat. It will render out and you will know immediately whether the duck is fishy or not. If it is, you will smell it. Turn off the heat and know you got a stinky spoony. If not, your are good to go.
Hope this helps.
I love all of God's creatures, properly prepared.