In case you missed it, the following is the latest survey results from Taupo Fishery Managers (with photos from TRM’s library):
Where else in NZ is the average trout over six pounds?
The winter spawning runs are in full swing, keeping river anglers very busy this year. Reports confirm most anglers are catching plenty of prime fresh-run rainbows. Data from the Waipa trap echoes the experience of anglers, with fish appearing in high numbers and good condition, only slightly down on the size and weight of the exceptional fish experienced in 2022.
If you have not yet managed a fishing trip to Taupō, you still have a month or so before the rainbow trout migration starts to tail off. So, block out some time in the calendar and come and experience some world class winter trout fishing!
We have good news for those who prefer to target trout in lakes – Lakes Otamangakau and Rotoaira are about to kick off their fishing seasons. Given the popularity and reputation of Lake Otamangakau, it should come as no surprise to hear this edition of the newsletter has a bit of a ‘Big O’ theme – setting the scene for opening on Sunday.
Along with our usual technical updates, this edition highlights minor tweaks to the fishing regulations for the Taupō District. We also reference the Taupō Fishery Advisory Committee trip to the Te Whaiau fish trap, and a reminder about invasive gold clam.
Finally, remember to head over to the Taupō online licence store and pick up your fishing licence before you start fishing. We have a variety of licence types to suit a range of fishing needs:
www.doc.govt.nz/FishingLicence
Lake Te Whaiau, linked to Lake Otamangakau via a canal.
Lake Otamangakau season about to kick off.
If you like to target very large trout in small scenic lakes, then we have good news – the fishing season at Lake Otamangakau is underway – from Sunday 1st September.
1 September marks opening-day at this popular stillwater venue and judging by the trap data there will be plenty of big fish around this year. Trout in Lake Otamangakau have a much easier time spawning, compared to their Taupō cousins. This means they often return to the lake in relatively good condition and make a full recovery. This partially explains why Otamangakau trout, particularly hens, tend to live longer, spawn multiple times and grow big.
Trap data suggests there are a good number of trout around the 8 to 9lb mark. These fish could easily reach the double-figures over the coming season. A summary of the data collected from the Te Whaiau spawning trap can be found in a separate story in this newsletter.
Anglers should also benefit from a reduction in aquatic weed this season, following a control operation carried out by Genesis – details below.
Finally, this treasured trout lake currently remains free of invasive gold clam. Let’s keep it that way by following all Check Clean Dry protocols. Pay particular attention if you are moving a boat between waterways.
The heaviest fish trapped during the 2024 season weighing in at a whopping 12.2lbs (5.55kg).
Te Whaiau trap summary.
The Te Whaiau Stream is the most important trout spawning site in Lake Otamangakau. Trapping was discontinued at the Te Whaiau fish trap in 2016 due to the huge demand it placed on fishery management resources. However, changes to the fishing regulations at Lake Otamangakau prompted a re-evaluation. Trapping resumed in 2022, as part of a broader monitoring programme to help track the impact of the new regs.
This year trapping started 7 June and operated until 5 August – providing 60 days of data. We had two flood events, where stream levels breached the top of the trap. The new improved trap design performed well, was easy to clean and quickly returned to operation.
During June, a total of 169 rainbows and 78 browns were trapped and processed by staff in the upstream pen (Table 1). In July, a further 289 rainbows and 11 browns were also trapped, taking the actual total to 458 rainbows and 89 browns over the trapping period. Each fish was sexed, measured, weighed, fin clipped, maturity estimated and then released upstream to continue spawning.
Adjustments were applied to allow for meaningful comparisons between the two-month trapping period of recent years and the five-month trapping period used in earlier years. Separate formulas were used for the browns and rainbows based upon the historical trapping data (1994-2013). The June-July period alone accounts for more than 95% and 88% variations in the total run of rainbow and brown, respectively. For rainbows, the formula is 1.42x(June + July actual count) +57.46 and for browns 1.12x(June + July actual count) +445. With these formulas applied, the run estimate for the browns increases to 545 trout and the rainbow trout run increases to 708 (Fig 1).
Trends in the abundance of rainbow and brown trout in the spawning runs remained similar until the mid-2000’s, when they started to show marked differences. The spawning rainbow trout population steadily increased from 356 trout in 1994 to 1,439 in 2005 but then surged after 2006 to reach a peak of 3,661 trout in 2009.
The increase in spawning run size was associated with a marked decrease in average weight for both browns and rainbows, especially between 2007 and 2013 when the numbers of browns and rainbows exceeded 3,000 trout in total. The increase in spawning biomass was particularly large for rainbow trout which increased from 997kg in 1994 to 7,116kg in 2010 compared to an increase from 790kg to 2,504 kg for brown trout during the same period (Fig.2).
The browns trapped this year averaged 605mm and 2.8kg (6.2lbs) with an average condition factor of 43.9 (Table 2). The heaviest brown was a hen measuring 670mm and weighing 4.45kg (9.8lbs). The longest brown trapped was a hen measuring 700mm. In comparison to the record-breaking 2023 trapping season, the browns trapped this year were on average 12mm shorter and 100g lighter. Overall, the browns trapped this year were the third longest on record and were comparable to those trapped in the mid 1990’s. Similarly, the browns were also the fourth heaviest on average this year and on par with those trapped during winters 1995 & 1996.
The rainbows trapped during 2024 averaged 617mm and 3kg (6.6lbs) with an average condition factor of 45.5 (Table 2). Overall, they were the third equal heaviest (same as 2023) but behind the peaks of 3.1kg observed during winters 1995 & 1996. These fish were similar in length to those trapped in 2022 and 2023. The heaviest rainbow trapped this year (feature image) was a hen measuring 690mm and weighing a whopping 5.55kg (12.2lbs).
Trout in Lake Otamangakau continue to grow once they have reached sexual maturity and after each spawning event. This post-maturation growth can create trophy-sized trout as older trout tend to be larger. Therefore, repeat spawning and longevity are important in maintaining Lake Otamangakau as a trophy fishery.
Females dominated the rainbow trout run by almost 2:1 which is consistent with the rainbow M: F sex ratio of 1: 1.9 observed each winter since 2022 (Table 3). Changes in the adult sex ratio towards an abundance of females tend to reflect a population of older fish that have spawned several times. Spawning tends to be harder on males who spend longer in the streams spawning with females and engaging in aggressive interactions with other males. As a result, females are more likely to survive the rigours of spawning causing the sex ratio to subsequently favour females.
The sex ratio of male to female brown trout (1: 7.9) this season had females almost outnumbering the males by 8 to 1. Historically, females have generally outnumbered males by one and a half to two times but never as much as 8 times. Only 11 brown males were trapped over the two months and so the extremely low number of male browns will have influenced the sex ratio. Jacks often run earlier than hens, so extending the duration of our trapping season may provide a better insight into this relationship.
Overall, the size and condition of the trout were on par with recent years again indicating that we are still dealing with a smaller population of larger fish. The size of the run was also comparable to recent years and up slightly on last year.
After the new upper size limit of 550mm came into effect on 1 September 2022, we saw 9 double-figure fish appear during the 2023 winter run. Only 2 double-figured fish were trapped during winter 2024 but it was very encouraging to see a good number of fish around 9lbs (4kg) that should reach double figures if they survive over the next 12 months.
Looking ahead, the ease of operating the new trap and the ability to leave it unattended should allow us to extend the trapping season next year by at least 4 weeks (mid-May to mid-August). This will enable the collection of a wider spread of primary data, which will provide additional insight into the population dynamics of this unique trout fishery.
Report update from Taupo Fishery Management Newsletter – Taupō Fishery Focus.
By trout anglers for trout anglers.
Issue 36 – August 2024.
