More than 30 dead eagle rays and two rig sharks have washed up at Porirua Harbour, north of Wellington, and Biosecurity New Zealand is now testing samples to work out what killed them. Volunteers stumbled on the animals during a routine beach clean-up on Sunday afternoon, and the size of the kill has unsettled people who have walked this stretch of coast for years.
Lorraine Shaab from the Wellington Coast Clean-Up Crew was leading the group that found them. She said the timing of the low tide was the only reason the rays were visible at all. Speaking to RNZ, she said the discovery was hard to take in.
“We started at 2.30pm at low tide because that’s the only time you can cross the inlet to where the rubbish accumulates, and unfortunately, that’s how we saw all the rays,” she said. “It was just heartbreaking.”
Some of the rays were lying on exposed mudflats and others were still in the water. The animals were spread across a fairly small area rather than scattered along the whole shoreline, which is part of what caught the volunteers’ attention. A social media post from the Petone Beach Clean Up Crew, another local group that helps keep the harbour edges clear, said the find was unlike anything its members had come across before.
“We have not seen anything like this before,” the group wrote, describing the rays and two rig sharks as sitting “all relatively close in one area” and still appearing fresh when they were found.
Eagle rays are a common sight in Porirua Harbour, especially over the warmer months when they glide across the shallow sand and mud flats hunting for shellfish and worms. The New Zealand eagle ray can grow to well over a metre across and is harmless to people, using its flat crushing teeth to deal with hard-shelled prey rather than to bite. Rig, a small shark sometimes sold in fish and chip shops as lemonfish, also uses the harbour as a nursery. Seeing dozens of them dead in one place is well outside what locals expect.
Biosecurity New Zealand sent specialist staff to the site on Monday to collect samples for testing at an animal health laboratory. Mike Taylor, who manages the agency’s aquatic health team, said staff were keeping an open mind while the results came back, but two natural explanations were front of mind.
“We suspect that the mortality could have happened due to the recent stormy weather or potential predatory action from orcas,” he told the New Zealand Herald. The agency has not ruled out an exotic disease, which is one of the reasons the samples are being sent away for laboratory work rather than the cause being called on the spot.
The orca theory is not as unlikely as it might sound. Killer whales are regular visitors to Wellington Harbour and the wider coastline, and rays are one of their favourite meals. They are known to herd rays into shallow water, where the rays can become stranded or exhausted, and drone footage earlier this year captured orcas hunting stingrays off Wellington’s south coast. A pod working a shallow harbour like Porirua could drive a large number of rays onto the flats in a short space of time.
The recent weather is the other obvious suspect. A strong front swept across central New Zealand late last week, bringing heavy rain, flooding and slips to the lower North Island and the top of the South Island. Storm surges and a sudden flush of muddy freshwater into a shallow harbour can lower oxygen levels and disorient fish and rays, and a run of bad weather can leave animals stranded as tides shift. Whether either factor, or a combination, is behind the Porirua deaths will not be clear until the test results are in.
The Department of Conservation has been told about the event but will not be running the investigation. Karen Middlemiss, a senior marine science adviser at the department, said staff were aware of the mass death but pointed out that neither eagle rays nor rig are protected species, which puts the response in Biosecurity New Zealand’s hands rather than the conservation agency’s. Newstalk ZB reported that the testing is the main avenue for getting answers.
For the volunteers, the find is also a reminder of how much life moves through Porirua Harbour, an inlet that has had its share of pressure over the years from sediment, stormwater and run-off. The same clean-up crews who pull rubbish out of the mudflats are often the first to notice when something is wrong, and on Sunday they ended up logging a wildlife event rather than a litter haul.
Biosecurity New Zealand has asked anyone who comes across dead or distressed marine life to report it through its pest and disease hotline rather than handling the animals, which helps the agency build a picture of whether the Porirua deaths are a one-off or part of something wider. For now the harbour’s eagle rays are back to their usual quiet routine in the shallows, and the wait is on for the laboratory to say what happened to the ones that did not make it.
Have you seen the eagle rays in Porirua Harbour, or noticed unusual numbers of dead fish or rays on your local coast? Share what you have spotted in the comments below.
This article was written by AI, briefed to report the facts, hopefully without some of the bias people bring to the job 🙂
Leave a Reply