Fish survey holds vital clues

Fish survey holds vital clues on whitebait and fairy tern in Waipū Estuary

Water quality in our Bream Bay rivers holds the key to the survival of many vital fish and bird species, particularly the declining native whitebait/inanga and the endangered tara iti, also known as the New Zealand fairy tern.
The journey began with a fish survey initiated by the Waipū About Tern community group. In March 2021, an algae bloom coincided with the blockage of the Waipū Estuary at its ocean entrance due to weather events carrying sand and sediment to the southern side of the groyne. This led to a significant loss of eels, fish, and other aquatic life, posing not only public concern but also a potential long-term threat to bird and fish species, like tara iti, dependent on the estuary for their food source. They breed mainly at – Mangawhai, Waipū, Pākiri and Papakānui – where river, estuary, or harbour and ocean merge to provide essential food sources.
Prompted by these events, members of Waipū About Tern approached researcher Ian Southey to monitor the estuary’s recovery. The two-year fish survey, beginning in June 2021, focused on four known tara iti foraging spots held by the males that return to Waipū.
The initial survey in June revealed a lack of fish in the upper reaches of the estuary at Estuary View Heights. Limited water circulation and low dissolved oxygen concentrations delayed recovery. The species found in this upper estuary included 15 goby, 222 sea hares, and 26 sea slugs, with sea hares playing a crucial role in seaweed and red algae clean-up. Unfortunately, this setback forced the resident tara iti male to abandon the area, impacting subsequent breeding seasons.

On a positive note, the river area below the cemetery emerged as a thriving location, with goby as the predominant species. Subsequent surveys indicated that this river location could potentially be a nursery for various fish species, reinforcing its significance to tara iti foraging territories in our waterways.
By July 2021, the upper estuary saw a slight increase in fish, while the river site maintained a diverse and abundant fish population. Glass goby emerged as the predominant species in the upper estuary by October, signalling encouraging trends in fish recovery across multiple locations. Over the survey period, the Waipū Estuary showcased a rich variety of native and endemic fish species, vital to tara iti’s diet. The fish species netted, measured, and returned to waterways include inanga (whitebait), estuarine goby, glass goby, bridled goby, kahawai, grey mullet, yellow-eyed mullet, triple fin, sole, smelt, sand diver, parore, estuarine stargazer, pygmy sleeper, cling fish, and small tuna (eels).
With two years of research completed, ongoing efforts will involve regular sampling from September to December each year.
The estuary, however, faces challenges from sediment runoff during heavy rain and storms, affecting water clarity and disrupting the habitat. Estuaries play a crucial role in supporting diverse bird species, linking their health to broader conservation efforts for bird populations. Sediment runoff alters waterway dynamics, negatively impacting seagrass beds, a critical nursery for fish. This has resulted in persistently low inanga numbers in both the Waipū River and estuary since the sedimentation event.
Healthy local waterways are at the heart of a newly established project led by Piroa Conservation Trust to set up and support catchment groups in Bream Bay. By connecting farmers and landowners along water corridors, the project can help to fence and replant riverbanks, remove willows, restore wetlands, and fish passage. These changes are known to reduce nutrient, sediment, and bacterial concentrations.
With funding from the Ministry for Primary Industries (MPI), this project is already well underway with catchment coordinator Graham Matthews. To get involved contact Graham on 027 432 1016 or [email protected]
Together, we can forge a pathway towards a healthier, more sustainable future for our Bream Bay rivers.