NZWR released 14799 juvenile Grass Carp into Lake Kereta between March 2008 and April 2009 to combat the problematic pest weed known as Hornwort.
Since the release occured in 2008 the Grass Carp have reduced the Hornworts presence by 99.9% of the previous levels (according to the NIWA report) which were noted by NIWA in 2008 as being approximately 75% cover of the lake bed. In Short this meant that over 3.5 years the Grass Carp ate 20 vegetated hectares of Hornwort, around 280 tonne dry weight of weed!
The project is still not over as there are trace remnants of the weed but the next stage of this project is to now wait and see how effective the Grass Carp are at eating Manchurian Wild Rice.
For information and the NIWA report about this project follow the link ‘PUBLICATIONS & PRESS’ to ‘HORNWORT REMOVAL IN LAKE KARETA’