Waipa trap reports - 2021 winter season

Short Summary of the 2021 trap season

The 2021 trapping season was significantly disrupted due to a Covid Alert Level 4 lockdown and flood events that totalled around 37 days of lost trapping time. This is the longest period that the Waipa fish trap has not been operating during the critical period of April to December, so a low actual count of trout was to be expected. A solid sample of kelts were obtained this year and this allowed us to adjust the actual run with some confidence.

Adjusted brown trout figures were the lowest recorded at the WaipaTrap (183) and well below the previous 5-year average of 520. Similarly, the adjusted rainbow trout numbers were low (1,085) and down on the average for the last 5 years (1,596).

Brown trout averaged 567 mm and 2.4 kg (5.3 lbs) which is down slightly on the previous couple of years, but the average condition factor was exceptional (47) which was the highest observed since 2009. Worth adding the females averaged 48.2.

Rainbow trout averaged 505 mm and 1.6 kg (3.5 lbs) which is down slightly on last year but consistent with recent years dating back to 2017. The longest rainbow measured 620 mm while the heaviest weighed 2.5 kg (5.5 lbs). Condition factor was also impressive for the rainbows, with an average of 44 which is on par with the high of last year and the highest since 2000.

Looking ahead plans to tag fish and monitor their residence time above the trap will help refine adjustment calculations and structural adaptations to the trap with increase flood resilience.

November 2021

As expected at this time of year, the number of fish processed through the upstream pen is reducing - 99 rainbows were processed and 0 browns.

We continued to see a significant number of unclipped fish in the downstream pen. The numbers encountered in the last few months confirms a sizable percentage of spawning fish avoided the upstream pen due to floods and an unavoidable interruption to trap operations.

As previously described our technical team will factor these unclipped fish into a summary of the season giving a more accurate assessment of the overall spawning run.

Graphs and tables November 2021 (XLXS, 66K)

October 2021

Trap monitoring reveals the number of fish processed through the upstream pen has dropped significantly from the previous month. This confirms we are now witnessing the tail-end of the rainbow trout spawning run. The absence of browns confirms they have finished running.

Rainbow trout numbers are nearly double those recorded in October last year (140 compared to 75) and the average size is very similar. Condition Factor (CF) was very good and continues the trend we have witnessed over the last couple of years.

It is worth noting a high number of unclipped fish were trapped in the downstream pen. These fish will have avoided the upstream pen due to a flood event or the temporary interruption to trap operations due to COVID. Therefore, these will not have been processed or captured in the upstream data. Our technical team anticipate this scenario. The number of unclipped fish will be factored into a summary at the end of the season, giving a more accurate assessment of the overall spawning run.

Graphs and tables October 2021 (XLXS, 66K)

September 2021

This is the first full month of data collection since June. It confirms fish numbers are up considerably compared to both last month and September last year. The figures recorded last month were compromised due to COVID-19 work restrictions, so the most valuable comparison is with 2020.

We can see Rainbow trout numbers are much greater than September 2020 (266 compared to 152), although average size was slightly down. Condition Factor (CF) continues to be very good, with a slight improvement on the good condition witness in 2020.

After the slow start to the year, numbers suggest the spawning run is later this year. However, given the significant interruptions to upstream data collection we will not get a good sense of this year’s run until we review information from the downstream pen.

Graphs and tables September 2021 (XLXS, 66K)

August 2021

COVID-19 Alert Level restrictions impacted data collection this month. Migrating trout could pass freely through the trap for several days as Fishery Rangers were unable to carry out monitoring and processing work.

Data collection resumed once staff were authorised to continue, but clearly the figures only reflect a percentage of trout that passed through the trap. These fish may have escaped initial monitoring, but they can still be identified in the downstream pen of the trap.

The absence of a fin clip will allow fishery staff to recognise them. The number of unclipped fish is then reconciled with the upstream data to give a better approximation of the overall size of the run.

Graphs and tables August 2021 (XLXS, 66K)

July 2021

Data for this month shows the arrival of rain has finally increased the number of fish passing through the trap. The number is higher despite the trap being taken out of commission for a couple of days due to a significant flood event.

Many trout were seen bypassing the upstream section of the trap, so these fish will have escaped initial counting. They will however be identified in the downstream pen – allowing us to factor their numbers into a final tally at the end of the season.

The average size and CF of both brown and rainbow trout is generally higher than last month but slightly lower than this time last year. The largest fish was a brown jack that measured 680 mm and pulled the scales down to 3.7 kg.

Graphs and tables July 2021 (XLXS, 66K)

June 2021

Data gathered this month reveals the number of trout processed at the fish trap was very low, which continues the theme witnessed in May. A comparison with the high numbers recorded last year is striking. This differential reflects the nature of a wild trout fishery and is likely linked to the low rainfall experienced for most of the month and the very low flow rates experienced in this elevated spawning tributary of the Tongariro River.

Fish length, weight, and CF is generally up compared to last month but once again, lower than recorded last year.

Looking ahead, it will be interesting to see how the significant rainfall forecast for July will impact the data.

Graphs and tables June 2021 (XLXS, 66K)

May 2021

The fish trap was recommissioned, and initial data collection got underway. However, with very low flow levels in the Waipa Stream and a minimal number of trout entering the trap it was decided to suspend daily trap monitoring until June.

As you might expect the number of fish recorded is low and reflects only two weeks of data collection. While data collection was suspended trout were able to move unhindered through the trap. Without a fin clip, these fish will be easily identifiable on their return journey – downstream pen of the trap.

Minimal rainfall and low flow rates may be contributing to the later start to trout spawning runs this year. It will be interesting to see how the situation changes once significant rain arrives.

Graphs and tables May 2021 (XLXS, 66K)