Karapiro Elver Transfer Summary 2016/2017
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).