He and the other 200 were transported to M8G-352, an off the grid planet, as a means of preventing them from leaving. The Atlantis expedition told them that they were suffering from a plague which caused memory loss. Merrick was one of those people who was trained to distribute the retrovirus until Dr. Carson Beckett would be able to make it permanent. However, Merrick was one of the few (roughly thirty) Human-form Wraith that realized something was wrong. These few managed to get together and form a plan, even though they were getting daily doses of retrovirus.
Merrick was one of small group who Lathan tried to convince to attack the soldiers and take their ship, and perhaps one of the ones who later helped Michael Kenmore, the ringleader, to kill Lathan after he ran away trying to prove that something was wrong. It is unknown if Merrick survived when Dr. Rodney McKay fired on the planet from above with a Hive Ship. However, it is likely as he and many of the Human-form Wraith were last seen in the camp before the ship opened fire. (SGA: "Misbegotten")