Painstakingly slow fieldwork completed this month is part of an acoustic survey project monitoring fish populations in Lakes Wakatipu, Wānaka and Hāwea.
Otago Fish & Game ecologist Jayde Couper said a Fish & Game boat was equipped with a high-powered echo-sounder supplied by Niwa.
"Some people may have noticed lately a Fish & Game boat ambling slowly around our big lakes," Mr Couper said.
"We’ve been scanning the lake edges down to a depth of 50m where most trout and salmon are likely to be found.
"Now that we’ve put in time on the water, the analysis starts back at the office."
Analysis will be completed by mid-year.
The acoustic survey is conducted with a Fish & Game boat following precise GPS transects scattered throughout the lakes. These routes are consistent with previous surveys carried out by Niwa in 2007, 2008, 2009 and 2023.
"Fish & Game uses various other methods to monitor our fisheries, including spawning surveys, drift dives, electric fishing, environmental DNA testing in tributaries and analysis of angler surveys and competition data," Mr Couper said.
"Acoustic surveys complete the picture, providing a valuable index of fish populations in the lakes.
"Knowing the state of our fisheries helps us set regulations that protect them for future generations, while still allowing plenty of fishing opportunity and providing a source of healthy, locally sourced wild kai."
To enable consistent year-on-year comparisons, the sounder is calibrated, and specialised software analyses the data to calculate fish numbers and the volume of water surveyed.
"Fish & Game is grateful to Niwa for loaning out the sounder, which is basically a super-sensitive fish finder."
Nets and cameras are also deployed to improve target identification with the sounder.
Recent angler surveys show Lakes Wakatipu, Wānaka and Hāwea are respectively the second, third and fifth-most popular freshwater fisheries in Otago, accounting for more than 30% of the region’s angling.
