It depends on the breed.
Humans have bred hybrids and genetically manipulated some breeds to be prolific all year layers, such as khaki campbells and runner ducks, amongst many others, although they take a short break in winter due to light/temp reduction.
Other less "domestic" and therefore nearer to their natural type breeds are more seasonal, such as mallards and muscovies. If they are hatched in 2010 you might have to wait until Spring 2011 (like me) for them to start laying.
You also need the right diet, conditions, etc. to keep them laying (and healthy and happy of course!).
What breed do you have?