Research project reaches 20-pound milestone

Angler Scott Miller landed a huge 20-pound (9kg) brown trout in the Tekapo Canal in April 2022, catching the attention of Central South Island Fish & Game.

Central South Island Fish & Game Officer Rhys Adams said, “although a 20-pound trout is literally gigantic, they are relatively common in the Mackenzie Basin’s hydro canals”.

“20-pound trout get caught weekly at the canals, but this is the first time one of our tagged trout has reached that size – it’s a milestone for our research project,” says Adams.

Since March 2020, 812 tagged trout have been released into the Tekapo Canal as part of a research project that assesses the growth and movements of trout that migrate downstream into the canal from its headwater, Lake Tekapo.

Mr Adams says, “the growth rates achieved by Scott’s trout and other tagged trout reported to Fish & Game are phenomenal.” 

“We tagged and released Scott’s trout in July 2020 and at that time it was 415mm long and estimated at 1.5-2 pounds. Approximately 22 months later, Scott estimated the same trout to be 20 pounds. So that equates to about 10-pounds (4.5kg) of growth per year.”

“But there is an even more phenomenal example of growth reported, a tagged brown trout that experienced about 14 pounds (6.3kg) growth per year. That is remarkable considering most trout in Lake Tekapo only reach a maximum size of three to five pounds (1.3-2.3kg)”.

Adams says, “these finding shed light on beliefs held by some anglers that the ability of canal trout to reach gigantic sizes is limited to trout born and bred in the canals and that only old trout can grow to gigantic proportions.”

Above Right: Scott Miller presents his 20-pound tagged brown trout before release back to the Tekapo Canal - Photo credit Morgan Brown

“Tagging programme results suggest that trout of any origin can reach huge sizes in the canals given their unique food sources and habitat and that growth can be so rapid that relatively young fish, potentially only two to four years of age, may reach 20 pounds.”

“There is still much more to learn from the tagging program, and we encourage anglers to report their catch of tagged trout,” says Adams.

The tags are coloured strips set by the dorsal fin; they all have a unique 4-digit number – that’s the key piece of information to report. Other information to report includes the locations of catch, date caught, whether it was kept or released, and estimates or better yet, measurement of length and weight.

A tagged rainbow trout with the yellow tag shown in the red circle - photo credit Rhys Adams

Tagged trout catch reports should be made to the Central South Island Fish & Game – email: csi@fishandgame.org.nz, phone: 03 6158400.

Central South Island Fish & Game wishes to remind anglers that the upper part of the Tekapo Canal, upstream of its State Highway 8 Bridge, is closed to fishing from June 1 to 31 August.

Year-round fishing is available at the Mackenzie Basin hydro canals, at the Tekapo Canal downstream of State Highway 8 and at the Pukaki and Ohau canals.