How early is too early

[letterman1]

Hello everyone, what time of year do you start downriggin for salmon.  My buddy and I have been out a few times on our yaks, I went out to 40' and marked a few fish at 25'.  I was told that some species come in shallow at this time of year.  I'm out of Whitby, Ontario, water temp was low 40's.  Thankyou