All at sea: El Niño may blow in a summer of scarcity for our seabirds

Veronika Meduna

Science & environment writer·New Zealand Listener·

10 Oct, 2026 06:04 PM4 mins to read

‌

Subscribe to listenAccess to Herald Premium articles require a Premium subscription. Subscribe now to listen.Subscribe now

‌

SaveShare this article

Reminder, this is a Premium article and requires a subscription to read.

Copy LinkEmailFacebookTwitter/XLinkedInReddit

Edin Whitehead checks on a fluttering shearwater chick at the Tāwharanui sanctuary in the Hauraki Gulf. Photo / Rikki Taylor

It’s official – this El Niño season is hitting the highest strength category, according to an index that tracks the relative ocean warming in the eastern and central Pacific compared with the tropical region.

This will drive stronger south-westerly winds and rougher coastal seas, but because New Zealand sits
on the edge of the El Niño system, its effect on weather patterns is complex. Earth Sciences NZ marine ecologist Matt Pinkerton says we can expect cooler waters but also more marine heatwaves, especially during summer, which will change how much phytoplankton – the single-celled algae that drift in the surface layers of the ocean and are vital to the food chain – grows where.

The El Niño effect comes on top of ongoing ocean warming, which reduces vertical mixing, Pinkerton says. “The upper ocean layers get more buoyant and aren’t as easily mixed downwards by the wind or waves. This slows down the supply of nutrients to surface waters and tends to inhibit phytoplankton growth, especially around the North Island.”

This in turn leads to a redistribution of zooplankton, the tiny animals that feed on phytoplankton. These changes are happening just as seabirds begin their breeding season and need to find enough food in the ocean to take to their colonies on land, says Edin Whitehead, a research fellow at the University of Auckland, whose focus is on how seabirds are affected by ocean warming.

Seabirds have some capacity to deal with variable ocean conditions because they are long lived. Smaller species, such as the diving petrels and fluttering shearwaters Whitehead monitors in the Hauraki Gulf, can live into their 20s or 30s. They feed on zooplankton and during a bad season may abandon a breeding attempt and try again a year later, Whitehead says. “But the problem we’re seeing now is persistent warming. So every season’s different and we’re starting to pick up signs that the adults are struggling to feed their chicks at those times of year.”

Seabirds are long-distance travellers. During the non-breeding season, petrels and shearwaters cover huge ocean distances in search of zooplankton. Whitehead says the birds return to certain places, probably based on past experiences of finding food, and may have some awareness of seabed features where upwelling of colder, nutrient-rich waters is more likely.

Diving petrels migrate all the way to regions with strong upwelling at the Antarctic polar front to feast while they moult. Fluttering shearwaters remain closer to the coast, but during the breeding season, with hungry chicks on their nests, both species are constrained in how far they can travel. “Both species normally provision their chicks quite frequently, ideally daily, so they can’t go much further away if the seas around their colonies are hot.”

Whitehead’s monitoring results from last summer show this growing strain. Diving petrels breed earlier, with most of their chicks usually fledged by December, and they are somewhat “buffered from the really high summer temperatures”, Whitehead says.

But for fluttering shearwaters, warm seas during December and January, when they are still raising their chicks, meant much longer foraging trips. A comprehensive study of breeding behaviour from 2015 – “probably one of the last normal sea-temperature years we had in the Hauraki Gulf” – showed adults bringing food to their chicks every day. Now, some birds spend up to 11 days foraging. “We know they’re working harder and spending longer to find food.”

Whitehead expects this will happen again this summer as food sources shift. “When we have these changes in ocean conditions it can mess with the instinctual baked-in timings these birds operate on because they’ve evolved to maximise when those food resources are available in different parts of the ocean.”

Pinkerton says for fish, the disruption could continue beyond the El Niño summer as species move with the food or to maintain their preferred temperature range. For fisheries, this may bring reduced catches or changes to the mixture of species.

“There’ll be some species that do really well from it, and some that do really badly.”

SaveShare this article

Reminder, this is a Premium article and requires a subscription to read.

Copy LinkEmailFacebookTwitter/XLinkedInReddit