Mr Sherburn said in the deeper lakes such as Tarawera, Okataina, Rotoiti and Waikaremoana trout are beginning to frequent depths of 15 metres or more, and this trend will continue and become more noted as the summer goes on.
"By mid-January expect the thermocline, a layered band of water where the temperature change occurs, to be well formed and trout to spend most of their daytime at this location.
"The exception is from dawn onwards when the lakes are at their coolest. Smelt often feed near the surface for the first few hours of light and trout find them easy prey. Whether you're spinning, fly fishing or trolling, you'll want to be up with the sparrows to catch the action early."
Some morning surface activity might continue for several hours, but other times it's over just after dawn.
Mr Sherburn said Lake Rotorua's stream mouths were also a key area during periods of warm weather.
Browns and rainbows are also swimming up the Ngongotaha and Waiteti streams, and shore-based anglers are advised to target the stream mouths after dark.
Fish & Game staff trapped and released 30 brown trout per night over a 10-night sampling period through their Ngongotaha Stream trap during November, the average weight nearly 3kg.
Eastern Fish & Game is holding a free boat fishing talk at Lake Tarawera at 10am on January 4, at Stoney Point reserve, off Spencer Rd. No bookings are needed. The sessions will include advice on what methods work best at which time of year and tips on how to de-bone and cook your trout.