Date: 23 July 2013
Recent finds of home-made traps designed to catch koura (freshwater crayfish) have alarmed the team trying to eradicate the noxious weed, lagarosiphon, from Lake Waikaremoana.
When the team of divers, headed by project manager, John Adams, found an abandoned commercial koura trap in April they were extremely concerned. The traps "could well provide a vehicle for the transfer of new aquatic plant introductions."
Since then, the discovery of three more home-made traps and 60 tailed koura bodies at Rosie Bay points to this practice being more common than previously known.
Koura are native freshwater crayfish, and like all native species, are fully protected within Te Urewera National Park. It is illegal for anyone to attempt to trap, catch or eat them.
As well as being illegal, the traps are a real threat to the "incredibly special and fragile environment" that is Lake Waikaremoana, said Cam Speedy from Genesis Energy at the Lake Waikaremoana Lagarosiphon Steering Committee Meeting hosted by the Department of Conservation at Aniwaniwa.
DOC, Genesis Energy, NIWA, HBRC, NZ Fish & Game, the Friends of Te Urewera, Iwi, and other groups in the local community are all working together to eradicate lagarosiphon from Lake Waikaremoana, which reappeared in the Lake in 2010.
It is not just about stopping lagarosiphon though. Dr John Clayton from NIWA points out that there is a real need to prevent other weeds like hornwort getting in "as that is by far the most serious weed and will have a much bigger impact".
"Incredibly invasive," it is "10 times worse than lagarosiphon" and could easily be brought to Waikaremoana on koura traps.
Which is partly why Waikaremoana kaumatua, Neuton Lambert and DOC Biodiversity Ranger, Riki Winitana were both appalled to see the latest find, a koura trap made from a converted lampshade. With fragments of weed clinging to its netting shell it clearly showed how it could be a vector for invasive weeds in Lake Waikaremoana. Trapping koura in Lake Waikaremoana is a "real no-no", said Riki. It endangers a protected species, threatens the whole Waikaremoana environment – and carries the risk of very heavy penalty fines for the perpetrators.
DOC would like everyone to remember that we can all help to keep the nasties out of our beautiful Lake by complying with the law and by following this simple code:
Check, Clean, Dry all equipment when coming to Lake Waikaremoana. This includes boats, anchors, trailers, fishing gear and nets. This should be done with the simple solution 1+1+1, which means 1 cup of salt in 1 litre of water, and leave to soak for 1 hour.
Two previous infestations of lagarosiphon have been successfully eradicated from Lake Waikaremoana; originally in 2000–2007 at Rosie Bay and then a smaller re-infestation in 2010.
Notes on lagarosiphon:
- grows in mud substrate, but can also be found growing in stoney areas and rocky crevices
- can mostly only grow to depth of 6m, below this the water pressure crushes the plants cell structure
- Fast growing. Lagarosiphon can grow at a rate of 10cm/day in favourable growing conditions (water temp 20–23ºC and optimum sunlight)
- Tiny fragments can break off the plants, if these fragments sink onto mud substrate they will grow into new plants
- Has ability to outcompete all other aquatic vegetation in the lake. Lake Waikaremoana has extensive native carophyte meadows which could be completely overtaken by lagarosiphon
- Lagarosiphon reduces the availability of oxygen to fish, and can impede fish access to spawning areas.
- Lagarosiphon can form large floating mats and have a major impact on recreational activities including: restricting boat access, impeding shoreline fishing, masses of rotting lagarosiphon washing up on beaches etc.
- Lagarosiphon causes major issues for power stations in the South Island (blocking up water intakes and impeding electricity generation).
- Stands of lagarosiphon increase sedimentation.
- Native to South Africa, brought to New Zealand in 1950.
- Doesn't set seed in New Zealand so spread between water bodies via vegetative fragments dispersed by human activities (not spread by birds).