Taupō Fishery Focus.
By trout anglers for trout anglers.
Issue 30 – August 2023.
August has seen large numbers of rainbow trout migrate up Taupō rivers. This has been very good news for anglers, who report landing some great conditioned fish.
A couple of relatively dry months on the Central Plateau had restricted the size of our early winter spawning runs. A change in barometric pressure and a bit of rain was all it took to trigger the rainbows into action – during one session Fishery Rangers processed over 70 trout migrating up the Waipa Stream (a spawning tributary of the Tongariro River). River levels have been low for the time of year, so nymphing has been the most successful method, particularly using patterns with a splash of colour. Unsurprisingly, ‘glow bugs’ have been working exceptionally well at times.
There’s also good news for stillwater anglers, with the fishing season at Lake Otamangakau due to kick off on Friday 1 September. In this newsletter you can read about the latest information from the Te Whaiau fish trap, located on the main spawning tributary for Lake Otamangakau – an ideal opportunity to whet your appetite for the new fishing season.
This newsletter also includes other technical insights into the Taupō fishery, along with advice on fish guts and an update on invasive gold clams.
If you are planning a fishing trip make sure you buy a Taupō fishing licence before you go fishing. Simply head over to our ‘online licence store’ – www.doc.govt.nz/FishingLicence
Alternatively, pop into one of the local tackle stores, they will be very happy to set you up with a suitable Taupō licence, along with any other fishing supplies you may need.
Remember to carry your licence with you when you go fishing.
Tight lines.
James Barnett
Editor
Lake Otamangakau season opens Friday.
The weather forecast looks promising for opening day at Lake Otamangakau on Friday 1 September. If you are planning to head up to the lake it might be worth taking a quick look at the forecast before you leave – early season weather can be fickle here!
The latest fish trap data confirms the fishery is doing well – both brown and rainbow trout have a high average size and condition factor. The focus on protecting large trout should generate even more trophy fish for anglers to target this season.
We will closely monitor how the new regulations continue to bed-in, with data from the Te Whaiau spawning trap providing a valuable insight. A short summary of the latest analysis is provided below.
Te Whaiau fish trap.
The fishing season at Lake Otamangakau is about to open, so it is timely to present a short summary of the latest data captured from the Te Whaiau fish trap.
The Te Whaiau Stream is the main spawning location for trout in Lake Otamangakau. This winter the trap was operational for two months (June and July) which allowed us to capture the back end of the brown trout run along with a significant proportion of the rainbow trout run. This is the second consecutive year the trap has been operational following a 5 year break.
A total of 321 rainbows and 50 browns were processed through the upstream pen, which included 9 trophy sized fish (exceeding 4.9kg or 10lbs). The biggest trout was a rainbow jack that measured 730mm and thumped the scales down to an impressive 5.5kgs or 12.1lbs.
To make a meaningful comparison with previous years (where the trap was operational for five months at a time) we need to apply an adjustment to the figures. We know June and July accounts for more than 95% and 88% variations in the total run of rainbow and brown trout, respectively. These formulas were applied, and information presented. (Fig.1).
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 numbers of trout recorded may be down, but the average weight and condition factor is much improved. The rainbows trapped during 2023 averaged 618mm and 3kg (6.6lbs) with an average condition factor of 45. Overall, they were the third heaviest behind the peaks of 3.1kg observed during winters 1995 & 1996 (Fig.3). There were 8 trophy sized rainbows recorded, which is the highest number since 2005. It is also encouraging to note that a further 16 rainbows weighed between 4kg and 4.4kg (8.8lbs and 9.7lbs) suggesting they will reach the magic double-figure mark over the coming season.
Although the browns were the longest on record, only 1 trophy sized fish was physically trapped; an impressive hen tipping the scales at 4.95kg or 10.9lbs and measuring 665mm. However, it is worth noting that June and July is the tail-end of the brown trout run so it is likely that more trophy sized browns ran earlier in the season before the trap was operational. Anglers reported catching trophy sized browns in Lake Otamangakau during last summer and so it is likely some of these browns spawned in the Te Whaiau Stream earlier in the winter or in the neighbouring Papakai Stream. The presence of some notably large brown unclipped kelts this year in the downstream pen would further suggest that these fish ran earlier. The average length and weight of trapped brown is still impressive compared to previous years (Fig.4).
Trout fishery modelling results suggest a maximum size limit is the best approach to preserve trophy-sized fish. The current maximum size limit of 550mm which came into effect on 1 September 2022, combined with a February closure, has certainly had an immediate impact on the number of trophy trout present in this winter’s run and this bodes well for anglers next summer wishing to target the larger trophy trout in this unique fishery.
More technically minded anglers may be interested in a more detailed analysis of the Te Whaiau trap data, which we plan to publish shortly. Look out for details.
‘How to fish’ Lake Otamangakau.
An oldie but a goodie – if you are new to still water trout fishing or just need an insight into the techniques used to successfully catch trout at Lake Otamangakau, then this video clip is for you. Check out our YouTube clip – ‘Lake O on the fly>’
Counting trout in the cold.
Fishery Rangers ‘suited up’ and plunged into cold water – all in the name of science. The first drift dives of the season took place against a backdrop of snow on the ranges and water temperatures sitting at a frigid 7 degrees Celsius.
These first plunges allowed the dive team to assess the current conditions and determine how things have changed since the last drift dives in November 2022. This assessment was crucial given the devastation suffered in the upper reaches of several rivers following Cyclone Gabrielle in February. Fishery staff can confirm that all designated diving sections were deemed suitable for exploration.
While still early in the season, initial tallies show fish numbers are not as high as the remarkable figures recorded last winter – which were extraordinary in terms of both quantity and size. This year the trout numbers align more closely with previous years.
Most trout were observed to be holding in the deeper pools rather than the shallows. Redds at the tails of pools and the presence of young fry along the shallow edges confirm trout have been actively spawning. The most concentrated clusters of trout observed during August were found at the Hinemaiaia, where trout typically migrate earlier in the season.
Drift diving has been used as a consistent way to count trout in the Taupō region since the 1990’s, serving as a pivotal monitoring technique for fishery managers. Working collectively, fishery staff walk and drift downstream headfirst, meticulously tallying the number of trout making their way upstream past the divers. This monthly task takes place between August and November across 6 rivers. A specific stretch on each river is used ensuring a consistent approach to data collection. By comparing these counts with data from previous years, fishery staff can determine the timing of the peak spawning period.
These dives take place above the winter fishing limits therefore all fish will have successfully evaded capture by anglers. This explains the formal term given to the dives, ‘escapement counts’.
Fishery staff will continue to monitor these rivers as we progress into spring and the water slowly starts to warm up!
Trout waste on riverbanks.
Most anglers understand that harvesting trout is an important part of managing the Taupō trout fishery. The question is, should trout be gutted and cleaned on the riverbank or is it better to take them home intact?
In our experience most anglers take harvested trout home intact. In doing so they steer clear of any potential risks associated with leaving fish offal on the riverbank and importantly they avoid potentially breaking the law.
Find out more about the risks and options on our website – Trout waste on riverbanks>
Waipa trap data online.
Trap figures for August are yet to be collated however is is clear that activity in the trap increased dramatically this month, as evidenced by the 70 rainbow trout processed through the trap in a single day following a drop in barometric pressure.
At this time of year rainbows are keen to reach their spawning grounds and take every opportunity to push upstream. You can keep up to speed with trout migration data by visiting our dedicated webpage – Waipa trap reports, 2023 winter season>
More anglers carry their licence.
The angling community has responded positively to our reminder to carry a valid fishing licence when trout fishing in the Taupō District. The proportion of anglers now carrying their licence has increased, which saves a considerable amount of time for anglers and Fishery Rangers alike.
As a reminder, anglers fishing without their licence may receive a letter of warning or an infringement fine. The responsibility to provide evidence of a licence sits with the angler. Taupō Fishery Regulations are clear, anglers must carry a valid Taupō fishing licence at all times when fishing. Physical copies such as plastic and paper licences are ideal, and digital versions or evidence of purchase are also good. Worth adding, if you are relying on a digital file, it must be downloaded onto your phone to avoid potential problems caused by poor cell phone reception.
CCD to control spread of gold glams.
Check, Clean, Dry (CCD) is an important management tool to control the spread of gold clams, so please remember to always check, clean and dry your gear when moving between waterways.
Phase 1 of the Biosecurity NZ gold clam surveillance programme is complete. Tests confirm the pest species is present in the Waikato River, as far upstream as Lake Maraetai at Mangakino. Phases 2 and 3 of the surveillance programme are designed to broaden the search, to determine if the clams are present outside the Waikato River. Phase 2 focuses on tributaries of the Waikato particularly the Waipa River, while Phase 3 extends the search to a national level. Innovative eDNA sampling technology enables initial tests to cover a wide area, allowing on the ground surveillance teams to be targeted more effectively.
The freshwater gold clam (also known as the Asian gold clam) is a small invasive clam, discovered downstream of the Taupō Fishing District, in the Waikato River. Anglers should remain vigilant and report any possible sightings.
Specific CCD guidance relating to freshwater gold clams can be found on the MPI, Biosecurity NZ website>