Here is the full list of all 51 Summer in Mara achievements. It takes around 20-25 hours to unlock all of the achievements on Windows.
Catch one fish of every type.
Read all the messages on Puni Cave.
Sing the old Navy song on its base.
Build all the main structures on Home Island.
Ask Caleb to take you back to Qälis.
Cook 50 dishes.
Carry 99 oranges in the backpack.
Complete all the quests from Napopo.
Pay the mortgage on your boat.
Visit all the islands from Mara.
Complete all the quests from Ecco.
Defeat the Elit.
Recover all the chrystalis from the Door.
Complete all the quests from Taima.
Get all the Koa's outfits.
Complete all the quests from Rigatta.
Complete all the quests from Onzo.
Get one farm animal of each type for your island.
Complete all the quests from Noho.
Complete all the quests from Pilly, Milly & Tilly.
Unlock all the crops on Home Island.
Complete all the quests from Litio.
Complete all the quests from Mayo.
Complete all the quests from Awan.
Complete all the quests from Blu.
Complete all the quests from Akaji.
Complete all the quests from Aquila.
Beat Ereti in a race.
Get all the Koa's backpacks.
Get the boat to max level.
Complete all the quests from Taka.
Use the recycle bin 100 times.
Complete all the quests from Brram.
Cook 30 dishes.
Craft 60 objects.
Meet Dunna.
Sell objects for a total of 3000 coins.
Sell objects for a total of 2000 coins.
Unlock the mine.
Complete all the quests from Mûn.
Sell objects for a total of 1000 coins.
Craft 40 objects.
The sea is dangerous, next time get back to your boat before getting tired.
Cook 15 dishes.
Meet Saimi.
Collect 90 objects.
Craft 20 objects.
Remember...
Collect 60 objects.
Wake up after the tutorial.
Collect 30 objects.