Snapper nurseries and water quality

Water clarity is critical to life beneath the waves, particularly for juvenile snapper (Chrysophrys auratus), a species central to New Zealand’s fisheries. Research conducted in Whangateau Harbour, and recently published in the New Zealand Journal of Marine and Freshwater Research, shows how water quality shapes their survival – and why even the smallest coastal habitats deserve attention.

Snapper begin life as drifting larvae, soon settling into nurseries like Whangateau’s rocky reef. Between 2018 and 2021, scuba surveys documented hundreds of juveniles (20-70mm long) arriving each summer. Underwater video footage further revealed a key pattern – when visibility exceeds four metres, they feed almost entirely on plankton; below that threshold, they shift to benthic prey. This adaptability highlights a vulnerability – murky water, often caused by runoff from land-use changes and deforestation, restricts access to plankton, a vital food source for early growth.

As sediment increasingly burdens estuaries, such limitations could threaten snapper populations across the region.

Community efforts, like those led by Whangateau HarbourCare play a crucial role in addressing these challenges.

Small habitats can play an outsized role. Whangateau’s reef supports only a few hundred juvenile snapper, a modest number compared to the thousands found in northern seagrass beds like Parengarenga and Rangaunu. Yet, when the larger nurseries failed in 2019, smaller sites like Whangateau proved essential, bolstering stocks that underpin fisheries and coastal ecosystems.

Almost all subtidal seagrass in the Hauraki Gulf has already been lost, and with an uncertain future ahead, preserving every juvenile habitat becomes critical.

Boat noise presents an additional concern. Video evidence suggests juveniles react to fast-moving boats as they would to predators, ceasing feeding and seeking reef shelter. These observations remain anecdotal, requiring further study, but they hint at a potential stressor. If noise consistently disrupts feeding or displaces snapper from nurseries, it could compound existing pressures on their survival.

Land-based actions have far-reaching effects on marine environments. Fencing and planting native vegetation along waterways can make a huge difference – volunteering with local groups is a great way to help.

Sticking to vessel speed limits to reduce coastal erosion and boat noise near juvenile fish habitats and controlling earthworks to reduce sediment runoff are also practical steps.

While it’s not the case in Whangateau, more broadly, choices about what we eat – shifting to whole foods, reducing meat and dairy consumption – can also reduce runoff and protect our coastal waterways. Whangateau shows that clear water and calm nurseries are vital, no matter how small the harbour.

Dr Jessica Campbell completed her PhD on juvenile snapper at Leigh Marine Laboratory, University of Auckland, and now researches at AUT’s Human Potential Centre. A long-distance swimmer, she blends endurance and science to study what sustains us and our oceans.