Gatland's shift makes sense because the competition in Auckland for the starting first-five's role will become much tougher when Otere Black returns from the knee injury which has wrecked his 2018 season.
Black, who would have started the season as the top-ranked playmaker, will fight for the role against incumbent Stephen Perofeta once he regains his match fitness.
The Blues will probably look to sign a developing player to replace Gatland.
Gatland signed for this year on a full contract after being a part-timer at the Blues in 2017, started at No10 for the first four matches of the season but was on the bench for the following three against the Sharks, Chiefs and Sunwolves.
He started at No10 against the Highlanders at Eden Park, with Perofeta moved to fullback, but couldn't make the match-day squad for last weekend's defeat to the Jaguares and he was left out of the mix for last night's match against the Waratahs in Sydney, with Daniel Kirkpatrick again preferred as the inside back replacement.
All Black Sopoaga is leaving for English club Wasps at the end of the year.
The Highlanders have 23-year-old Fletcher Smith as Sopoaga's back-up, so Gatland should have an easier time of staking a claim for a regular starting spot in the deep south.
Gatland has performed well at times this season, and in particular in the first match against the Highlanders in Dunedin in February when he surprised with his pace and power.
He is likely to have fond memories of Forsyth Barr Stadium given that was where he helped his North Harbour side to their ITM Cup Championship final victory over Otago two years ago with a final-minute dropped goal.
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