Thesis on first aerial survey of ancient fish traps nets medal

Hundreds of years ago, the Khoe San used stone fish traps, or vywers, in the shallow intertidal waters of the Southern Cape to make a catch.

They worked at spring low tide, during the dark moon phase, mostly in the winter months.

Remnants of these ancient fishing cultures still remain between Mossel Bay and Hermanus. UCT's Lucy Kemp, of the Department of Zoology, conducted the first aerial survey of this heritage, material for her master's thesis. The thesis has now won Kemp the prestigious S2A3 Bronze Medal from the South African Association for the Advancement of Science.

The aerial survey included visvywers from Mossel Bay to Hermanus. Kemp used aerial imagery to map and geo-reference these so that the South African Heritage Resource Agency, which funded the flights and mapping, could have a complete database of the fish traps.

"We looked at the ecology of the fish traps and the surrounding rocky shore to see what effect the fish traps had on the ecosystem, and used this information to make inferences about the impact that current development will have on rocky shore communities," Kemp said.

Kemp built useful relationships with locals - including Johnny Appels, the last strandloper - the Arniston and Still Bay fishers teaching her how vywers work. These are made mainly from rock in situ, and the walls occur singly or in complexes of up to 25 traps.

Capricious weather also played a part in Kemp's project.

"We waited month-in and month-out for those nearly impossible conditions necessary for aerial photography - clear, windless, mist-free skies on a spring tide."

For the "ground truth" she was looking for, Kemp spent hours in the sea off Arniston and Still Bay in winter, in the small hours, waiting for the fish to come in, looking to see what was being caught - and how much of that catch was legal.

Studies show that the species caught in the vywers haven't changed in 50 years, including mainly mullet species (mostly Liza richardsonii) but infrequently catches of over-exploited line fish such as galjoen (Dichistius capensis).

"It's these catches that concern managers," says Kemp.