Waipa trap reports – 2023 winter season

November 2023

This was the final month of operation for the season, with the fish trap decommissioned on 1 December. Rainfall at the trap site was 176mm with no flood events recorded.

Rainbow trout numbers were in decline for the season, with 253 fresh-run fish processed compared to 334 the previous month. Brown trout have completed spawning.

Typical for this time of year the downstream pen accounted for more fish than the upstream pen, with 271 fish recorded. Downstream fish are checked for a current fin-clip and released to continue their journey. The proportion of unclipped fish provides an indication of how many trout evaded the trap during flood events.

Graphs and tables November 2023 (XLXS, 69K)

October 2023

Rainfall at the trap site was limited this month (134mm) with no flood events recorded. Significant rainfall in September ensured stream levels remained suitable for migrating fish.

Rainbow trout continued to arrive in good numbers, with 334 fresh-run fish processed in total. This compared with zero brown trout. These results are typical for this time of year - confirm brown trout have completed spawning.

Of the rainbows, 201 were hens and 133 jacks. The largest fish this month was a hen that weighed 2.35kgs, measured 620mm, with a Condition Factor of 49.3. Fin-clip scars from previous spawning migrations confirmed she was an older fish. The largest jack was a maiden fish on his first migration. He tipped the scales at 2.15kgs, 540mm, CF 49.3.

Graphs and tables October 2023 (XLXS, 66K)

September 2023

A single flood event restricted trap operation for four days. This was a rare occurrence this year given the dry winter conditions experienced on the Central Plateau.

The rainbow trout are reaching the peak of their spawning activity, while browns have largely completed spawning at this time of year. A total of 406 rainbows were processed through the upstream pen, consisting of 204 hens and 202 jacks. Only 22 browns were processed, all of which were hens.

The largest fish this month was a brown hen that tipped the scales at 3.75kgs, and measured 640mm with a Condition Factor of 51.6. Fin-clip scars confirmed this was her fourth consecutive spawning run, having previously passed through the trap in 2022, 2021 and 2020.

Graphs and tables September 2023 (XLXS, 65K)

August 2023

A small increase in rainfall saw occasional elevated flows through the trap but there were no flood events. Overall, the stream level remained low and clear. As a comparison we measured 130.5mm of rainfall at the trap site this August compared to 338.5mm in August 2022.

After a relatively dry spell, the drop in barometric pressure and increased rainfall triggered an increase in rainbow trout accessing the spawning tributary. We processed 258 rainbows through the trap – 124 hens and 134 jacks.

The heaviest was a hen that weighed 3.5kgs (7.7lbs) and measured 635mm. Scars from previous fin clips confirmed this fish to be a repeat spawner, having passed through the trap in 2019, 2020 and 2021.

At this time of year the brown trout spawning run is starting to decline. Rangers processed 72 fish The largest was a hen of 3.2kgs (7lbs) and 645mm with a previous fin clip scar from 2020.

Graphs and tables August 2023 (XLXS, 66K)

July 2023

Low rainfall persisted, with only 90mm of rainfall recorded at the trap site. The flow rate in the Waipa Stream resembled those typically seen in summer, affecting the number of trout migrating into this spawning tributary. In May, there was a significant run of 102 rainbow trout due to elevated rainfall (400mm). However, the numbers declined to 43 and 71 for June and July, respectively.

The urge to spawn will eventually force trout to migrate so we anticipate August will deliver an increase in the number of rainbows, even without significant rainfall.

The average size of trapped rainbows in July was 485mm and 1.4kg (3.1lbs), consistent with the overall trend this season. The largest rainbow trapped in July was a male measuring 575mm and weighing 2.2kg (4.9lbs).

During July, a total of 67 brown trout were trapped, indicating a continuous but reduced presence. The peak of the brown trout run occurred in June, with 109 trapped during that month. As we move into August, we expect the numbers to decline further as the brown trout run concludes for the season.

Brown trout trapped during July had an average size of 589mm and 2.5kg (5.6lbs), consistent with the patterns observed in recent months. The largest brown trout trapped during July weighed 3.25kg, slightly over 7lb.

Graphs and tables July 2023 (XLSX, 66K)

June 2023

Only 44mm of rainfall was measured at the trap site throughout June, with no floods recorded. This was very dry compared to nearly 400mm recorded during May. As a result, the stream level dropped significantly. The browns appeared to cope well with the reduced flow and good numbers continued to pass through the trap. The number of rainbows was down considerably on June 2022, when the stream level was much higher following over 350mm of rain.

A total of 109 browns were recorded with fish averaging 576mm and 2.45kg (5.4lbs) with an average condition factor of 45.8. The heaviest brown trapped during June was a hen measuring 670mm and weighing 4.1kg with a condition factor of 49.2. This hen was a previous spawner with a fin clip visible from the 2020 season. Only 43 rainbows were trapped during June and these fish averaged 485mm and 1.4kg (3.1lbs) with an average condition factor of 45.1.

Graphs and tables June 2023 (XLSX, 65K)

May 2023

This year marks the 26th consecutive year trapping trout as they migrate up the Waipa Stream to spawn. Cyclone Gabrielle caused enormous damage to the forests surrounding the trap, with fallen trees restricting vehicle, foot, and fish passage. It took fishery staff considerable time and effort to re-establish access. In addition, several large logjams were impeding fish passage upstream from the Tongariro River, so these were also cleared.

May was a wet month with almost 400mm of rainfall recorded. This is nearly double the figure logged during the same period last year. As a result, the trap was in flood on 3 separate occasions. Despite the extra floods, the runs for both browns and rainbows were up slightly in comparison to last year.

The average size of the rainbows in May was down in comparison to those trapped during recent years with the averages comparable to those fish from 2016. Traditionally we would see some larger fish early in the run as these have matured earlier. Time will tell whether the average sizes will improve over the coming months given the delayed productivity in the lake over summer.

The heaviest rainbow trapped in May was a maiden hen measuring 565mm and weighing 2.2kg (4.9lbs). Interestingly, almost 90% of the rainbows trapped were classed as maidens with very few previous spawners recorded. Perhaps some of these previous spawners struggled to recover pre-Christmas when productivity was low (having returned to the lake in very large numbers following the huge spawning run last winter). The next few months will provide a better indication of their survival as they may have just taken longer to recover as productivity improved.

Similarly, the browns were also shorter and lighter than recent years but were still in good condition. The heaviest brown trapped this year was a jack measuring 730mm and weighing 4.7kg (10.4lbs).

Graphs and tables May 2023 (XLSX, 64K)