380 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1950 



times in great abundance, and tliere is reason to believe that the shrimp 

 crackle might be a useful tool in establishing the whereabouts and 

 extent of sponge colonies. 



New methods of catching fishes, new gear, always excite the imagi- 

 nation and catch the public fancy. Since the war two inventions 

 have attracted particular attention. One, a new Danish floating trawl, 

 has been dubbed the "atomic trawl" because of the reports of its effec- 

 tiveness. Trawl nets are normally dragged along the sea floor to 

 catch bottom-dwelling species; the problem is to catch those forms 

 that exist in large numbers near the bottom but above the vertical 

 limit of the relatively flat cone-shaped net. The Danes are said to 

 have developed a method of making a trawl work some distance above 

 the bottom and to have made enormous catches thereby. Two boats 

 work some 300 feet apart and the gear is manipulated by a system 

 of floats and balances and by slackening and tightening the towing 

 ropes and wires. Published descriptions are complex and not encour- 

 aging to those who might like to experiment. It is probable that the 

 gear is effective in limited areas and under special conditions; the 

 Danes have always excelled in net construction and gear handling. 

 But the "atomic trawl" will not revolutionize the industry, nor will 

 it be a gear which will bring about a great increase in the world's 

 catch of fish. 



The other invention, developed in Germany by Dr. Konrad Kreut- 

 zer since the war, has been given the spectacular name "electrophysi- 

 ological fishing." Previous experiments had shown that fishes are 

 responsive to the polarity of electric fields, and when two electrodes 

 are placed in the water, with a varj'ing positive voltage on one, the 

 fishes are forced in that direction. Kreutzer has carried on experi- 

 ments in Lake Constance and, on a small scale, in salt water; he 

 reports great success and hopes to obtain a patent on the electrode 

 arrangement and on the pulse shape and rate, the pulse form being 

 critical to the success of the whole endeavor. Last summer (1949) he 

 was seeking funds to equip an experimental boat in order to attempt to 

 apply his method to the trawling industry. The anode would be in- 

 corporated in the net and the cathode kept near the boat. He has 

 not published quantitative results of his experiments to date and is 

 not willing to reveal all details until he has obtained patents. 



However, his accounts are highly enthusiastic and an American 

 Consulate report from Bremerhaven states, "Kreutzer's invention, if 

 successful, will revolutionize commercial fishing." The principle 

 would be applicable not only to the trawl fishery, but to other types 

 of gear, and the inventor believes it would be especially adaptable 

 to the capture of large forms such as sharks, tuna, and whales. Kreut- 

 zer himself grants that practical experimentation with electric fishing 

 at sea will unquestionably pose many technical difficulties. For ex- 



