Source: Environment Canterbury Regional Council
Thousands of tuna (eel) trying to migrate to the sea were stranded at Te Waihora/Lake Ellesmere last week, so we worked with Te Taumutu Rūnanga to clear the path for future migrations.
Rūnanga became aware of a large tuna migration, estimated to be 20 tonne, on Thursday night (3 April), and most tuna successfully made it to sea.
Many tuna became stranded, and while this is very sad, this is a natural event that occurs every year.
One of the natural triggers for tuna migration is the presence of seawater. On Thursday night seawater was washing from the sea into the lake, which likely triggered the urge to migrate.
Check out Ngāi Tahu’s video about the tuna stranding on their Facebook page.
About the tuna heke (eel migration)
Tuna heke is the phrase used to describe mature eels that migrate to the sea to spawn. These migrating fish stop feeding and undergo many physiological changes to prepare for their journey.
During the migration to the spawning grounds, they rely on stores of body fat to sustain them. By the time they spawn they are normally thin and die shortly after.
In absence of a lake opening, they will follow any pathway and unfortunately can find themselves stranded and perish.
The NIWA website has more information on tuna heke.
Working together to help the tuna
Tuna are an important taonga species for Ngāi Tahu and Te Taumutu Rūnanga. They are essential to the continuation of mahinga kai for Ngāi Tahu and the wider community at Te Waihora/Lake Ellesmere.
At the request of Te Taumutu Rūnanga, we sent machinery to the site and started work on Sunday morning to lower the beach crest so that further waves of migrating tuna will have a shorter and less steep journey to the ocean.
The earthworks to shorten the path for future migration are now complete and will last until shingle naturally washes into the area to fill it up again.
In consultation with rūnanga representatives onsite, the decision was made to bury the deceased tuna. Tikanga (custom) and its application is determined by the hapū.
Opening the lake
Te Waihora is the largest lake in Waitaha/Canterbury and has no natural outlet to the sea. It was opened by generations of Ngāi Tahu before Pākehā arrival. The first written settler’s record of an artificial opening between the lake and sea was in 1852. It has been opened over 300 times since.
The opening is governed by a National Water Conservation Order and a range of resource consents held jointly by Ngāi Tahu and us.
However, many groups have an opportunity to share their views before a final decision is made.
A full opening of the lake to the sea is very expensive and is a carefully considered process after consultation with a wide range of parties. The lake also naturally closes itself when shingle washes back into the cut and this can occur very quickly depending on sea conditions.
Other work we’re doing in the area
There is significant cultural and ecological long-term work being undertaken at Te Waihora/Lake Ellesmere to restore and rejuvenate the mana, mauri and ecosystem health of Te Waihora and its catchment.
The programme works in partnership with Te Rūnanga o Ngāi Tahu, us, Selwyn District Council, Christchurch City Council and Department of Conservation (DOC) to improve water quality, mahinga kai and biodiversity values, such as through wetland and riparian restoration.
Two significant projects in the programme are:
- The Whakaora Te Waikēkēwai project, led by Te Taumutu Rūnanga and co-managed with us, is restoring the mid-lower reaches of Te Waikēkēwai/Waikēkēwai Stream through riparian restoration, on-farm actions, and restoring a significant wetland for iwi.
- The Weed Strikeforce, which is delivered by DOC and co-funded by us, is restoring lakeshore wetlands at scale through targeted control of willows and woody weeds, fostering natural regeneration (Rejuvenating the mauri and ecosystem health of Te Waihora).
