Do small earthquakes affect fishing? After Monday’s 3.8 Hawke’s Bay quake, it was a struggle to catch anything

Fiona Anne postponed fishing after a magnitude 3.8 earthquake, believing it affects fish behaviour.

Fiona Anne had planned to head out on the water on Monday afternoon.

But after seeing a Hawke’s Bay Today story about a magnitude 3.8 earthquake south of Hastings giving the region a small jolt, she decided she would wait until later in the week.

Fiona’s been fishing in the geologically active region of Hawke’s Bay - and specifically Hawke Bay - for about 25 years.

Monday’s quake hit at 8.16am, and was classed as weak, at a depth of 36km.

In a region with the history of the 7.8 magnitude 1931 quake to fall back on, and the future threat of the giant Hikurangi subduction zone offshore, it was small fry.

But past experience has taught Fiona that the day would still have been a write-off.

“Our fishy friends are quite sensitive to earthquakes,” she says.

Though it’s a hobby, she says the patterns are hard to miss.

“There have been many times we’ve been out on the boat, and we’ve been trying every trick under the sun, and just wondering why we’re just not catching them,” she told Hawke’s Bay Today.

“And then we’ll check GeoNet and see that there’s been an earthquake, and then we’re like, ‘Oh, that explains it’.”

Fiona says she believes even the smallest earthquakes can spook the fish.

“With boat fishing, if there’s no earthquake, we’ll come home with 30 or 40 fish.

“But after an earthquake, sometimes we come home with nothing.”

Brent Howie, who fishes in Napier daily, was out on the water on Monday.

Hawke’s Bay Today asked him how it was going.

“It’s very quiet,” he said from his position.

While there weren’t a lot of bites, Howie has never made any correlation between a lack of catches and seismic activity.

“It’s been quiet the last few days due to the moon phase ... and also the wind.

“But I’m not too sure about how an earthquake would affect the fish.”

Jason King, a day trawler working aboard St Jude for Seafood New Zealand, said he was also unsure about the connection.

But he did notice a clear drop in catch off the Hawke’s Bay coast after Monday’s quake.

“On Sunday, we had 20 bins, which is 25kg in each bin, and on Monday, we had 12 from exactly the same shots.

“Two shots each day, and they were right in the same area.”

After 38 years in commercial fishing, King said he couldn’t be sure if that was related to the quake or just bad luck.

Wayne Bicknell, a Hawke’s Bay Sports Fishing Club member with 50 years of recreational fishing experience, believed the quakes “definitely have an impact” on fishing.

“You don’t catch them after quakes.”

Bicknell has fished through quakes of different magnitudes across the country over the years.

“It’s probably relative to the size of the earthquake. The bigger the earthquake, the more it has an impact, and the smaller the earthquake, the less it has, but it still definitely makes a difference,” he says.

Professor David Schiel, a marine ecologist at Canterbury University, said it was unlikely that minor earthquakes like Monday’s 3.8 jolt would have a significant impact on marine life.

Schiel worked on research after the 2016 earthquake along the northeast coast of the South Island, a massive 7.8-magnitude event that physically lifted parts of the seabed by up to six metres.

That quake permanently changed parts of the coast, destroying habitats and affecting key species.

In contrast, Schiel says, smaller quakes don’t usually result in any structural changes under the sea, but he says many people do believe animals are sensitive to them.

“Smaller earthquakes that just rattle and roll tend not to have any observable effects because they just disturb things for a while, and everybody goes back and then takes care of their own business.”