Monster trout catches are fur real

MOUSE DIET: Ewen Rodway shows off a 4.5kg (10lb) brown trout he caught on the edges of Lake Manapouri.

Fishermen have been catching unusually high numbers of monster trout this summer – and it's all thanks to a population explosion in mice.

Southland Fish and Game manager Maurice Rodway, whose son Ewen caught a 4.5kg (10lb) brown trout on Boxing Day, said anglers were catching the fattest trout seen in the region's rivers and lakes in about five years.

"The average size would normally be 3lb to 4lb ... but this summer they are 8lb to 9lb," Mr Rodway said.

There had been even a 7.7kg (17lb) trout caught, he said.

"That's just a story, of course, but I can believe it."

The reason for the abundance of fat trout being hooked was parts of the Fiordland beech forests had dropped huge amounts of seeds, known as a "mast year", resulting in huge food supplies for mice and other rodents.

With the glut of food available, the mice had more babies more often and when they went swimming in the region's lakes and rivers they were eaten by trout, who in turn had become fatter than normal, he said.

Invercargill fisherman Stan McDonald said his 16-year-old son Michael had caught a 4kg (9lb) trout on the Upper Waiau River a fortnight ago – bigger than anything his jealous but proud father had caught in 43 years of fishing.

"It was extremely fat, obviously grown on the protein of mice," Mr McDonald said.

Te Anau Fish and Game officer Bill Jarvie said the increased number of fat trout being caught was a silver lining to a dark cloud.

While the mouse population had exploded, so had stoats and rats, which was bad news for the region's native birds.

Department of Conservation Te Anau area manager Reg Kemper said it had identified places in Fiordland where birdlife would most likely be affected by increased rodent numbers this winter.

DOC staff, volunteers and community groups would be trapping accordingly.

"Anything that increases the stoat numbers has an effect on the native population," Mr Kemper said.

- © Fairfax NZ News