Pinched from DOC’s Taupo Fishery Focus
This was the 26th year of consecutive operation for the Waipa spawning trap and the driest on record, with summer-like flows through much of the winter season. Despite low stream levels the run of browns was the highest we have seen in 8 years, with great conditioned fish. The run peaked during June with 30% of the annual run (May-Oct).
Rainbows were a little shorter than the exceptional fish encountered in recent years, but they too were in excellent condition. The 2023 rainbow trout run peaked during September accounting for 34% of the annual run (May-Oct). Note, we focus on May to October when making comparisons because data from this period has consistently been captured over the years.
Size of the run.
Historically, the actual run used to be adjusted to account for fish missed during flood events but there were a lot of assumptions with the adjusted data. Instead, we have chosen to represent the actual number of trout trapped and also show the number of flood events that occurred each year to show the years where numbers of fish will likely have been missed.
The actual number of browns trapped this year between May and October was 359 and consisted of 218 females & 141 males (Fig.1). This is the highest run since 2015 and down slightly on the 26-year average of 374 trout. The run peaked during 2001 at 648 trout. The lowest run of 95 browns was recorded during 2021.
The actual number of rainbows trapped (Fig.2) during the same May to October period this year was 1,212 (616 females & 596 males) and is also the highest run since 2015 when the run reached 1,484. Overall, this year’s count is well down on the 26-year average of 2,536 but it’s important to note that the run between years 1999 and 2007 was more than double this year’s run. The rainbow trout run peaked during 2005 when 4,628 rainbows were trapped and reached a low of 421 rainbows during 2019.
Fish size and quality.
The brown trout trapped during 2023 averaged 578mm and 2.5kg with an average condition factor of 46.4. Rainbows averaged 490mm and 1.5kg with an average condition factor of 45.1. Both the brown and rainbow trout populations were broken down into 2cm length categories and the lengths plotted in Figures 3 & 4 to show the length distributions.
The average condition factor of brown trout was 46.4, the 5th highest since trapping began (Fig.5). This was down on the recent peaks witnessed in 2021 and 2022 where average condition factors had reached 47 and 49, respectively. Rainbows trapped this year had an average condition factor of 45.2 which is the highest average score since trapping began. This follows on from the previous peaks of 44 calculated for the last 4 years. Over 400 of the rainbows trapped (33.6%) had a condition factor between 45 and 50. Overall, 83.2% of rainbows had a condition factor greater than 40.
For context, average condition factor scores between 40 and 45 represents a trout population in average to good condition while anything above 45 indicates a population in excellent condition. Condition factors less than 40 generally reflect trout that are in poor condition. A slim kelt that had spawned and lost all condition may have a condition factor in the low as 20’s.
Timing of the run.
The female brown trout run peaked in August with 65 females trapped or 29.7% of the May to October actual run (Fig.6). The two peak months of July and August accounted for 114 females or 52.1% of the actual female run. The male brown trout run peaked during June with 62 males trapped (44.3% actual run) with months May and June accounting for 114 males or 81.4% of the actual run.
Female rainbows peaked during October with 208 being trapped (33.4% of actual May-Oct run). The two peak months were September and October and accounted for 412 females (66.2% actual run). Male rainbows peaked during September with 203 males trapped (34.2% of actual May-Oct run). August and September were the two peak months for rainbow males with 337 trapped or 56.8% of the actual run.
