Scientific Services

A gillnet is a wall or curtain of netting that hangs vertically in the water column and is typically made from monofilament or multifilament nylon. They are generally weighted on the bottom and have a series of floats along the surface line. The size of fish caught will depend on the size of the mesh but a wide range of species and sizes are potentially caught.

If used correctly gill nets can be a very efficient method for scientists to monitor estuarine fish communities and population changes over time. By limiting the time the net is in the water, selecting certain time periods to sample, and through continuous monitoring of the net scientists can get an idea of the number of species, relative abundance, and size structure of the fish community whilst minimising and even preventing any unnecessary fish mortality.

However, when used illegally by poachers the netting can have severe impacts on estuarine fish populations. Poachers set nets to maximise catches, the nets are not monitored and are left in the water for long periods of time (typically at night) and the mesh size is generally small which means many juvenile fish are caught. Otters, terrapins and various bird species including cormorants and greater crested grebes are also caught from time to time in these nets. The use of gill nets is not only environmentally destructive but has a negative impact on both recreational and subsistence anglers. By removing large numbers of fish the catch rates within these more responsible and sustainable fishing practises is reduced and the sustainability of local fisheries is threatened.

The gill nets that SANParks remove have typically been constructed by sewing discarded netting material that is used to secure pockets of vegetables to pallets while being transported to retail and distribution centres. Discarded polystyrene, plastic bottles and just about anything that can float is used to float the top part of the net and stones are used as weights to create the wall of net. The poachers that set gill nets make use of canoes that are stolen or borrow canoes that are kept on the water’s edge or at slipways. The canoes are used to row to a concealed place and the nets are set. Canoes are hidden in the reed beds to be used at a later opportunity.

To try and prevent the usage of this packaging material SANParks has been engaging local vegetable suppliers and creating greater awareness around the problems associated with illegal gill netting. This approach has been beneficial with local vegetable suppliers being very co-operative and more careful with discarding the packaging material when their delivery of fruit and vegetables arrive. Unfortunately some this material still slips through into the wrong hands. Limiting the availability of boats also hinders the poachers and residents of Wilderness and Sedgefield are discouraged from keeping their canoes or small boats on the water’s edge.  A valid SANParks vessel permit assists greatly with tracking the owners of a canoe that is found abandoned and we encourage all boat owners to register their boats and canoes with SANParks.

The interception and removal of gill nets from the Touw River and Swartvlei estuary is a high priority for Wilderness Rangers. Gill nets are not only illegal but can be a highly destructive and indiscriminate form of fishing that threatens local fish populations and their sustainable use. Recently SANParks Wilderness Rangers destroyed 3 363m of gill nets that have been removed from the Touw River and Swartvlei Estuary over a 36 month period. That’s enough netting that if you laid it out along the N2 it would form a continuous barrier stretching between the Market on the Island and the Sedgefield Arms.