SCENARIO RULES: The Attacker automatically wins Initiative in the first turn. The Defending player may only act normally with his ships if they first pass a Crew Quality check (target number 10). If a ship fails this check, it must move 6" (or up to it's maximum speed if less than 6) in a straight line. The defending player's fighters may all act normally.
It doesn't specifically say that the CQ check is for the first round only, but I'm sure that's the intent. In the 1e version of Ambush the defender couldn't act at all in the first turn and a number of players took that to mean that the ships were at speed 0 (so no dodges, and could be boarded, and could All Stop And Pivot next turn) and I'd take the change in 2e as a fix for this.