Mamea, a No 8 who has played 26 games for the union and also played two tests for Samoa, is waiting to sign a contract with the Centransa El Salvador club.
The club is coached by former Otago and All Black prop Joe McDonnell.
McDonnell had been playing for Newcastle in the English premiership but left at the end of the season to start a coaching career with the Spanish club.
Mamea (29) said he was still waiting for a contract to arrive but hoped to sign it in the next couple of days and then intended to leave for Spain next week.
He would not play for North Otago this Saturday against Poverty Bay.
The Spanish season starts at the end of this month.
Former New Zealand sevens star Justin Wilson is also a member of the Spanish club, which won the Spanish championship last year and has qualified for the European Challenge Cup.
North Otago coach Mike Mullins admitted the loss of Mamea was a blow to the union but was meeting last night to decide on a new captain for the side.
Veteran openside flanker Ross Hay seems the likely choice.
Mamea, a freezing worker, said he had been contacted by an agent, who had brokered the deal.
It was a tough decision to leave North Otago, especially being captain of the side, but the opportunity to play professional rugby was too good to turn down.
Mamea first played rugby for Nelson Bays in 2001, before moving to North Otago in 2005.
He was a member of the Meads Cup-wining side in 2007, and said yesterday that was the highlight of his time with North Otago.
Mamea played two tests for Samoa in 2000, coming off the bench both times in tour matches against Wales and Scotland.
North Otago opened its season with a 26-22 loss to South Canterbury in Oamaru on Saturday.
