Dozens of harmless visiting sharks great news for Wellington

An adult rig shark.
An adult rig shark. Photo credit: NIWA

Dozens of visiting sharks have astounded swimmers at Wellington's Oriental Bay. The sharks themselves bring good news - their presence indicates a healthy inner-city harbour.

Long, hot evenings have had Wellington's bays packed with visitors both terrestrial and marine.  

On Monday afternoon, hoards of baby rig sharks swam around the legs of paddlers, with the occasional 1.5m shark making an appearance in the shallows.

Newshub political reporter Lloyd Burr was among the swimmers. He said he could see small rig sharks, big stingrays and a whole lot of jellyfish.

"It was pretty magical. It was a lovely way to end the day," he said. "They came very close."

As the sun set at 9pm, people came out with their torches, catching glimpses of the sharks.

Shark researcher Riley Elliott says the visiting sharks are harmless rig sharks, commonly known as lemon fish - the main staple of fish and chips.

"Rig sharks are totally harmless. They are from 30cm as a baby to 1.5m adults. They have sandpaper-like teeth and eat fish and crustaceans. They are absolutely harmless to people," he said. 

The sharks are an indicator species, showing the harbour is in good health, he said.

He said an increase in shark sightings is probably down to one factor - the heat. 

Warm weather is attracting both sharks and people to the beach, and the presence of smart phones means we're more likely to hear about it when people bump into a gilled predator.

The sharks come in to digest a meal and then head back into colder, deeper waters to feed.

"Shark often use warm water to regulate their metabolism because they are a cold-blooded species," Mr Elliott said. 

"You can often find sharks sunbathing so they can digest."

The warmer waters are also changing the distribution of species.

Sharks, jellyfish, stingrays and dolphins have all been spotted in Wellington's harbour in recent days. Mr Elliott says that's partly because warming waters have caused more algae blooms, leading to more phytoplankton - a "catalyst to the food chain" - attracting birds and fish, and then stingrays and sharks, into the harbour.

The Department of Conservation advises swimmers to give the wildlife space and says people should not attempt to chase or touch the sharks.