Carping on about Groenvlei

GARDEN ROUTE NEWS - Groenvlei Lake and carp problems have become synonymous over the past few years, with the invasive fish proving more than a handful for those seeking to conserve the quality and biodiversity within the lake.

Carp is regarded as one of the world's 100 worst alien species, and has been slowly wreaking havoc in Groenvlei since it was illegally stocked in Groenvlei in the 1990s.

The carp population has steadily increased ever since, and in February 2020 CapeNature estimated that there was 160 tonnes of carp in Groenvlei (60 000 fish).

The carp have over the years led to a fish die-off because of declining water quality, to the collapse of a once outstanding bass fishery, and their presence also caused high turbidity due to algal blooms.

The turbidity reached a point in early 2020 where Groenvlei's water was transformed into a muddy colour with a visibility of less than 10cm, according to Johnny Snyman of Invasive Fish Species Management (IFSM), the organisation leading the fight against carp in Groenvlei. IFSM was only founded in late 2020 / early this year, but is a culmination of years of work by Snyman and the teams he works with when going out on the waters at Groenvlei.

Snyman and his crews have been battling carp in Groenvlei's water since May 2018 through means of bowfishing and netting.

As the name implies, bowfishing is a method of fishing that uses specialised archery equipment to capture the fish. The work they have done in the little more two-and-a-half years since, has yielded impressive results - more than 14 tonnes of carp have been removed from Groenvlei in this time.

Johnny Snyman prepares to head out onto the water in the early hours of the morning.

According to Barend le Roux, CapeNature landscape manager, they have benefitted from a partnership with the South African Institute for Aquatic Biodiversity (SAIAB), that carries out their carp population assessments at Groenvlei.

"Carp data captured between 2014 and 2020 shows that carp population density is more or less stable," Le Roux said, noting that the bowfishing and netting have proved effective.

The large amount of carp hasn't been wasted, however, and during the Covid-19 pandemic it has proved to be a very crucial means of food provision for some of Sedgefield's poorer communities.

In a joint initiative between CapeNature, Knysna Municipality and Gift of the Givers, the use of carp as a food solution had provided food relief to hundreds if not thousands of people in need. The air bladders in carp have even been cleaned, dried, and turned into nutritious 'dog chappies' too.

But, remember the water turbidity mentioned earlier? In 2019/2020 the high turbidity led to the water taking on a very brownish hue. Le Roux notes that while the brown coloration has improved, according to SAIAB, water turbidity has also increased from last year.

SAIAB has sent water samples to the South African Environment Observation Network (SAEON) for further testing.

IFSM is a non-profit organisation, and relies on community assistance to keep its projects going. If you'd like to lend a hand, you can contact them via their Facebook page.

The crew sets out for an early morning trip on Groenvlei. Photos: Supplied