Figuring out stocking survival rates is extremely difficult and each body of water will have a slightly different model to go by depending on fishing pressure, habitat availability, and forage. I would also agree with icedflies, Splake are a hybrid mix between lake trout and brook trout and do not reproduce. They are stocked solely to be used as a sport fishery.
Also if you were looking for a good lake to target them on, Sporley can produce a lot of fish, especially in the early and late season.