With a late season (?) anglers have still been asking SWMBO difficult questions about trout spawning habits as they have failed to run on time?  (“on time” means when the anglers were here.)  Many have been regularly visiting Turangi at about the same time every year for many years so they confess their frustration when the trout do not arrive on time.  Why is that?

So TRM have dug out some historic specifications to reply… to compare how it used to be.  Back then the trout were obviously better trained to keep to the anglers’ time table.  Some suggest the spawning patterns have changed since?  This provides  interesting reading to see how much has changed as a specific study was done on the Tongariro River.

Following copied from the excellent book “LAKE TAUPO” (x- Page 126) co-ordinated by D J Forsyth & C Howard-Williams as part of the old DSIR Information series in 1983 – 35 years ago but still relevant.  The chapter on “TROUT FISHERY – HISTORY & MANAGEMENT” was contributed by P. Burstall – a well known former Conservator of Wildlife in the Department of Internal Affairs – before it was converted into DOC – the Department of Conservation.  Some frustrated fishless conspiracy theorist anglers (aka inmates) have suggested DOC should be blamed for changes to the spawning runs?

“In the Taupo rivers and streams there appeared to be three distinct spawning runs:  (1) a small summer run mostly of immature fish of both specieswith brown trout dominant; (2) an autumn run of spawning brown trout, and (3) a winter run of spawning rainbow trout.  Spawning itself followed about one month later.  A few rainbow trout spawned throughout the year and there was considerable overlap of spawning activities between the two species.

The males ran before the females which remained about two months in the stream, losing 25% of their body weight.  Males remained for about three months in the streams and lost about 30% of their body weight.  There was about 20% natural mortality during and following spawning. Stream flooding seemed to stimulate a mass return of fish to the lake, with few rainbow trout remaining in the tributaries in summer.  Body metabolism and development of the reproductive organs occurred at the expense of body flesh as little or no feeding occurred during spawning.  After spawning the fish took about eight months to recover condition.  This showed that poor conditioned fish were not deceased as was thought in the 1940’s but were post spawners or kelts.

After spawning the fish ranged throughout the lake, but usually returned to the parent stream for the next spawning.  They rarely migrated into neighbouring tributaries, and never entered tributaries on the opposite side of the lake.  Rainbow trout spawned in successive years, although brown trout sometimes missed a year…

Although brown trout make up no more than 2% of the anglers catch, trap data indicated that they made up approximately 20% of the total trout population, had a higher weight and lived longer than rainbow trout.

A specific study was made on the Tongariro River.  All tributaries were trapped simultaneously for 14 days to collect data on the total angling effort.  The results showed that anglers caught mostly older fish in the river.  These had a heavier average weight but a lower than average condition factor.  As these fish were all post spawners they were generally unacceptable to anglers.  The Tongariro River data were similar to those obtained from traps in other tributaries all of which showed that anglers tended to catch old post spawning fish.  This is important when considering changes to the angling season.”