When I laid my sod by the pond I just got a few bags of topsoil and sprinkled it along the seams so it was a little higher than the sod and then used a leaf rake to smooth it out. Worked pretty good and then the bermuda filled in.

Bob

Good advice from Bob. Use soil or sand and let it settle in between the pieces. Sand is usually heavier and settles in faster. The grass will soon cover the filled-in seams. If you live near a creek with a sandy bottom and sandy banks take your truck and help yourself.