Improving lake good news for fisheries
Wednesday, 22 January 2014 9:00 a.m.
Lake Rotoiti water quality is the best it has been in decades and this can only be good for fisheries say experts from Fish & Game, NIWA and Bay of Plenty Regional Council.
Regional Council General Manager Natural Resource Operations, Warwick Murray, said water quality improvements were a result of interventions through the Rotorua Te Arawa Lakes programme and that was great news for the community, the Crown and the programme.
“The Ohau diversion wall has been extremely successful in improving water quality. This, coupled with sewage reticulation, has meant we have reached the water quality target for the lake,” Mr Murray said.
“The wall was constructed in 2008 and diverts nutrient rich waters from Lake Rotorua entering Lake Rototi. This is allowing us to see improvements in Lake Rotoiti now and gives us the time needed to make the sustainable changes necessary to secure long term water quality improvements,” he said.
“At the same time we must make sure our interventions don’t have any adverse effects on lake ecology or fisheries and we have a fish monitoring programme in place to monitor the long-term effects of the diversion wall on smelt, trout, koura and kakahi,” Mr Murray said.
The Regional Council leads the fisheries research and monitoring with assistance from NIWA, Fish & Game and Ian Kusabs & Associates. Data has been collected and reviewed for the last seven years, including a period of two years prior to the wall’s construction, by an independent panel of New Zealand fishery experts.
“The latest results from the Fish Monitoring Programme have been very positive,” he said
NIWA Principal Scientist Freshwater Fish Group Manager Dr David Rowe said the results of the smelt monitoring programme in 2012/13 indicated several runs had occurred in the channel over spring.
“The results confirm that strong upstream migrations of both adult and juvenile smelt are occurring with the diversion wall in place.”
Smelt are the main food source for trout and NIWA monitors their channel runs using traps and combining the data with morning and evening observations of smelt movements and shag and gull numbers.
Dr Rowe said larval smelt in Lake Rotoiti also appeared to be increasing as lake water clarity improved.
Eastern Fish & Game Manager Rob Pitkethley said the start of the current trout season was the best on record since surveys began three seasons before the wall went in and this spring’s fishing was a large improvement on the past three seasons.
“Schools of smelt were noted running through the channel prior to the opening in October, and the runs of smelt have lasted through November, which has not been seen for a number of seasons,” Mr Pitkethley said.
“Trout caught in the channel have been in better condition compared to the last few seasons. Recent highly productive smelt spawning from Lake Rotoiti appears to have translated through the food chain into good trout growth, in both lakes Rotoiti and Rotorua.
“Monitoring of the Lake Rotorua and Rotoiti fisheries has shown fluctuations in trout growth and condition, and some recent improvements. The absence of algal blooms and improvements in water quality on both lakes should be beneficial for the longer term health of these fisheries,” said Mr Pitkethley.