Waipa spawning trap

Image: James Barnett | DOC

Introduction

A series of monthly reports sharing information gathered from the Waipa Stream fish trap.

Highlights

Located on the Waipa Stream, the Waipa spawning trap is positioned within a significant spawning tributary of the Tongariro River, 24 km upstream from Lake Taupo.

Fishery Rangers record the numbers of trout, their sex, length, weight and iteroparity (how many times individual fish have spawned). From this data we also determine a Condition Factor, which reflects how much food has been available to the trout.

This trap has been operational since 1998 and has provided a valuable long-term data set. We view this information in combination with a variety of other studies such as angler surveys, drift dives and lake productivity work, to ensure a broad understanding of fishery's health.

Date:  28 November 2019

October 2019 trap data

Data collected from the Waipa Fish Trap in October confirms the 2019 trout spawning run has slowed.

Compared to last month the number of fresh-run Rainbow trout has reduced, while there were no fresh Brown trout recorded at all.

Browns have completed spawning, so we would not expect to see them arriving at this time of year. Rainbows run later in the season, but their numbers also decline as conditions get warmer - although a continuous stream of spawning fish can be expected.

When we compare this month’s data with October 2018, we see an increase in both fish size and average weight, but condition factor was slightly down. The biggest difference, however, was the number of fish. Last year we had a late run that generated higher numbers, particularly rainbow hens – 95 (Oct 2018) compared to 54 (Oct 2019).

While data collection focusses on recording fish captured in the upstream section of the fish trap, this information doesn’t tell the whole story.

As mentioned in the September report, we also have a downstream pen which captures trout that have completed spawning and are returning to Lake Taupō. We continue to see many unclipped fish, which indicates they must have by-passed the upstream pen during flood events. That means the total fish run will be greater than the initial data suggests.

Our methodology anticipates this issue and allows fishery scientists to ‘factor in’ information on unclipped fish. This enables us to arrive at a more accurate assessment of the size of the actual spawning run. This information will be captured in a final report.

Anglers are reporting typical results for this time of year – good numbers of trout present in the Tongariro River. These fish are made up of a mixture of fresh and recovering trout. While some are struggling to overcome spawning, many were doing well on a diet rich in caddis. Small nymph patterns have worked well, particularly after a period of dry weather when river conditions are low and clear.

Graphs and tables October 2019 (XLXS, 72K)

September 2019 trap data

We continue to see good sized trout with a high Condition Factor (CF) pass through the fish trap this season, suggesting the fishery is currently in good health.

The CF for rainbow trout remains on a par with the excellent fish encountered last year, while the tail end of the brown trout spawning run is revealing some exceptional conditioned fish.

Data confirms rainbow trout hens are now starting to turn up in greater numbers, joining the jacks on the spawning reds – a higher percentage of males are recorded early in the season. Overall fish numbers remain steady, but at a lower level than we might expect for this time of year.

Interesting to note a number of unclipped* 'kelts' have been captured in the ‘downstream pen’ of the fish trap, which means they must have bypassed the trap during flood events earlier in the season. Therefore, the initial data will have underestimated the total number of trout present. We will continue to monitor the kelts to determine how many fish were missed. This approach forms part of a robust scientific process, which helps ensure the final data we analyse each season is as accurate as possible.

Looking ahead, we expect good fishing opportunities during October and November, as the remaining rainbows run the rivers regardless of weather – nearly 70% of Taupō rainbow trout run in the spring!

Graphs and tables September 2019 (XLXS, 67K)

*Trout have one of their fins partially clipped as part of processing. This enables fishery staff to recognise fish that have previously passed through the trap. With different fins clipped each year, it also allows fishery scientists to determine if trout have previously spawned, and if so, which year.

August 2019 trap data

Size and Condition Factor (CF) for trout processed at the Waipa spawning trap in August continued to be good, although we witnessed an unexpected drop in the overall numbers of fish counted.

Brown trout run earlier in the winter with their numbers peaking in July, so the reduction in their numbers was expected, but the lower than anticipated number of rainbow trout was a surprise.

Taupō is a wild fishery and this result falls within the level of variability we might expect from a dynamic wild system. In addition, a significant flood event ‘topped’ the trap structure which would have enabled a significant number of fish to bypass the trap. We will be able to quantify the number involved by recording unclipped fish that enter the downstream pen of the fish trap – this information will be combined with other data to provide a more accurate assessment of the season.

The number of rainbows trapped in August was down slightly compared to same period last year (88 compared to 124).

In terms of size, the comparison with this time last year is good - the average rainbows are both longer and heavier than August 2018.

The data from August aligns well with reports from anglers who said they had landed some cracking fish but finding them was a challenge at times.

Looking ahead, trends from previous years suggest nearly 70% of Taupō rainbow trout run in the spring. This can result in exceptional fishing on many rivers, particularly the Tongariro where trout will begin to run regardless of the weather.

Graphs and tables August 2019 (XLXS, 66K) 


Note: Graphs and tables are for the month, previous month and same month last year. 

Files include data below for brown and rainbow trout (male and female):

  • count
  • average length
  • maximum length
  • average weight
  • maxium weight
  • condition factor.

Previous trap data

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