Inanga Spawning.
Whitebait restoration project.

Wainuiomata Coast

Summary: Wainuiomata students spent their spring learning all about the life cycle of inanga, what threatens them and what they could do to help increase the population in their local area with the Whitebait Connection program.

Spring is the time of the year when white baiters head to the river mouths to try their luck at catching food for their families. This has become harder over the years with the declining number of whitebait. Whitebait are the juvenile of 5 different species of New Zealand native freshwater fish – four of these species have declining population sizes. This decline has resulted from damage to habitats, pollution to waterways and barriers to upstream migration and introduced predators such as slugs, mice and fish.

 
 

Picture: The five species of native fish caught as whitebait, with threat status. (from Forest and Bird)

Inanga are one of these 5 species that is most commonly found in the lower reaches of the river. They swim downstream in autumn to lay their eggs up on the riverbanks on a spring high tide. Eggs will remain there for 4-6 weeks. On the next spring tide, eggs will hatch out as larvae and get washed out to the ocean. Over the next six months larvae develop into what we know as whitebait before beginning their journey back into the river in spring.

 
 

Picture: The four different stages of the inanga lifecycle.

Student from Waiunuiomata High School and Konini Primary spent time down at the mouth of the Wainuiomata River this spring to investigate the health of the Wainuiomata River to see if inanga could survive. Students carried out water quality testing to see if the water was cool, clear and clean enough for the whitebait species. Habitat assessments allowed them to discover that some banks of the river are not stable enough causing mud to be washed into the river.

Picture Left: Konini Primary students checking what macroinvertebrates live in the river as food for the inanga.

Picture Right: Wainuiomata High student test the water quality of the Wainuiomata River.

After checking fish nets students were able to get up close with adult inanga and juvenile whitebait found swimming up the stream. Students were excited to see that there were fish living in the stream. They realised the need to improve the habitat for inanga by planting more trees to reduce sediment getting in the river and to create shade and cover. Sediment is the fine mud that settles between rocks, and removes important habitat for other creatures.

 

Picture Left: Inanga caught and returned to the Wainuomata River.

Wainuiomata High and Konini Primary students visited the mouth of the river a second time, but this time to plant trees donated by Greater Wellington Regional Council, with the help of park ranger Mark McAlpine. The students managed to get 120 plants in the ground in the morning. These plants will grow strong roots and help to hold the river banks together.

Picture Left: High school students helping primary school student get stuck in with planting trees.

Picture Right: Konini Primary students at the Wainuiomata River planting day.

This project was supported by funding from the Curious Minds fund. In 2017 we plan to have more students out in their local streams discovering important inanga habitats that can be restored to improve the number of eggs and therefore the number of whitebait we see in our freshwater environments.