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Marine heatwave brings fish bonanza
Red Emperor being caught as far south as Dongara. Picture: Gary Mitchell

The warm waters off Perth's coast this summer have recreational fishers whetting their appetites and wetting their lines.

After the marine heatwave of the 2010-11 summer, which continued last summer, another strong Leeuwin Current has again pushed prized subtropical species such as red-throat emperor and Rankin cod into metropolitan waters.

There are even reports of sailfish being hooked off Rottnest Island.

Reflecting on a great summer's fishing, Blue Juice Charters owner Gary Mitchell said his customers were catching species further south than ever.

"I think it's the cycle of the Leeuwin Current but it's well and truly out of the normal," he said.

"The red emperor, for example, is a really highly prized fish up north and now it's being caught off Dongara.

"The Robinson's sea bream - they're usually around Exmouth and now they're out just north of the (Rottnest) trench."

Mr Mitchell said he hoped the trend continued so he could offer a tropical fishing experience from his Hillarys-based business.

"All of these fish are really good eating," he said. "It's certainly a bonus at this stage. We're just hoping it continues and we end up having the coral trout, too."

But Gary Jackson, principal research scientist at the Department of Fisheries, said the changing conditions were not all good news.

While he could not help but share the excitement of Perth's recreational fishing community, he said there would be drawbacks.

"In terms of fishing charters, it only looks like great news to them and it probably is in the mid-term," Mr Jackson said.

"They can target a huge range of species they traditionally had to travel 1000km north to catch.

"But people need to be realistic about how nature works and the potential downsides.

"For example, there are tropical marine pests that we really don't want in the metropolitan area. The threat of losing a good blue crab fishery in the Swan River is a real risk.

"Abalone populations in the metropolitan area could also suffer through higher water temperatures."

Dr Jackson said that the Redmap project redmap.org.au, which was community-driven, was helping to map changes in the marine environment, for better or worse.