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2016/17 ELVER TRANSFER REPORT KARAPIRO

Another very successful season following last season’s record catch. This season started off very slowly with relatively low catches early in the season. The summer was marked by high river flows and frequent operation of the spillway, indeed late in the season spilling was almost continuous. Water quality remained relatively good without any major outbreaks of algal bloom in the lakes. Probably the highest flow regime since the capture programme commenced.

Normally transfers cease about the end of March, but as capture rates were still quite high EECo funded further capture into mid April until Elver movement ceased. This extra trapping accounted for over 200kg of extra elvers being transferred into Lake Karapiro.

A number of Elvers were also transferred by Waikato-Tainui / Ngati Korokii Kahukura into a couple of ponds in the Karapiro catchment as part of a customary fisheries enhancement project. Despite some quite major maintenance work being carried out at the Power station during the summer there were no adverse issues and the programme proceeded well. There were no problems with the capture or transfer equipment.

While not directly related, it is worth noting that due to the frequent operation of the spillways throughout the system as a result of unusually high rainfall, it likely resulted in a very successful spawning migration this autumn. If that is the case we may well see a marked increase in recruitment in the coming seasons.

The elver traps were first deployed on 29 November 2016 and the first catch (60.50 kg) occurred that night. Trapping and transfer of elvers continued for 151 days until 18 April 2107. There was a late pulse of elvers in April just before trapping concluded. The traps were cleared on 145 occasions and 32 samples of the elver catch were examined to determine the average weight and species composition. The lift trap was damaged due to wear and tear on 1 March, but was repaired by Mercury Energy and re-deployed two days later.

The total elver catch for 2016–17 was 2,100.19 kg (2,533,948 elvers), consisting of 221,467 longfins and 2,312,481 shortfins (Table 1 and Figure 1). The lift trap collected 1,358.15 kg and the stop Log trap collected 742.04 kg. The total catch was 1.4-fold greater than the median annual catch for Karapiro from the last twenty two seasons (1,656,000 elvers, n=22). There were no mortalities recorded during the operation of the traps in 2016–17. Samples were retained for aging studies (0.81 kg).

During the season 128.6 kg juvenile eels (946 eels) were also captured and transferred upstream (Table 2). In addition to elvers and eels, the trap operators estimated that a by-catch of 881 shrimp, 285 common bullies and 26 inanga were also transferred to the upstream hydro reservoirs (Table 2).

On a weight basis, the largest proportion was transferred to Lake Karapiro (38%), and the remainder transferred to lakes Ohakuri (16%), Arapuni (14%), Whakamaru (13%), Atiamuri (6%), Waipapa (3%) and Maraetai (10%).

Since 1992, we estimate that over 37 million elvers have been transferred to the Waikato hydro reservoirs from the trap and transfer operation at the base of the Karapiro Dam. The total includes 6.3 million longfin elvers. About 28% of the elvers have been transferred to Lake Karapiro (Table 3).