120 Man Against Shark 



towers on the beaches to a permanent enclosure, which was repeatedly 

 smashed by waves and in almost constant disrepair. 



The Durban nets are set about 800 yards off the beach, parallel with 

 it. Since the nets were installed, no bather has been attacked in Durban. 

 Careful records have been kept on the number of sharks netted each 

 year. In 1952, a total of 602 sharks were caught. A year later, the number 

 had dropped to 158. Since 1952, the average number has been about 170. 



Dr. David H. Davies, director of the Council of the South African 

 Association for Marine Biological Research, took a hard look at the 

 Durban meshing. As a marine biologist and a specialist in sharks, he was 

 baffled by the apparent effectiveness of the meshing as a shark barrier. 



"There is no really satisfactory explanation for the success," Dr. 

 Davies reported. "Although the nets extend for a considerable distance 

 parallel to the bathing beaches, they do not form a continuous wall, and 

 at all times sharks are able to penetrate the area between the beach and 

 the nets by swimming between separate nets or round the ends. Sharks 

 have been found to have been gilled on either side of the nets when 

 traveling both toward and away from the beaches. 



"The only reasonable explanation for the success of the set-net system 

 seems to be related to the already established fact that it is possible to 

 reduce a shark population by systematic netting. This has been shown 

 in commercial shark fisheries in various parts of the world . . ." 



Echoing Gilbert's words, Davies cautioned that "no completely re- 

 liable system has yet been devised for the protection of humans against 

 shark attacks." But, marine scientists have known for years that elec- 

 tricity often has weird effects on fish. In an experiment in Austraha 

 more than 20 years ago, an 11 -foot shark was seemingly paralyzed by an 

 electrical barrier. When the current was turned on, the shark would not 

 move; when the current was turned off, it swam away. 



More elaborate electrical experiments have been conducted on bony 

 fishes. When current is passed between two electrodes, with fish between 

 them, it has been observed that the fish turn to follow the current toward 

 the positive pole. The current does not attract them. Methods of using 

 electricity for commercial fishing have not been practical so far in salt 

 water because of the large amount of current required. Better success 

 has been had in fresh water, especially in Russia. 



Davies and Dr. J. P. Lochner of the National Physical Research 

 Laboratory in Pretoria, South Africa, recently tried an "electric fence" 

 on sharks. It seemed to work, they reported. Although they stressed 

 that their experiments were only preliminary, they found that an elec- 

 trical current passing between two electrodes acted as a barrier to sharks. 

 They also found that an electrical charge strong enough to turn back a 

 shark was not so strong that it would give a swimmer much discomfort. 



