Ngāi Tahu Mahinga Kai web Series. Episode xxx - The annual tuna migration from Lake Wairewa is a site to behold as the mature female tuna make their way across the shingle to the sea on their journey to Tonga. Local Ngāi Tahu take this opportunity to dig drains, sustainably harvest and process those not quick enough to escape. The locals, including our talent Iaean Cranwell are well known for their succulent, delicious smoked tuna.