Two recent developments show promise as radical new methods 

 of fish catching. One is the air -bubble curtain developed by our 

 New England scientists. The other is electrical fishing. It is 

 known that when fish come within the influence of an electrical field, 

 they orient themselves with respect to the gradient in potential and 

 swim toward the positive pole. The dissolved salts in sea water 

 create problems, and a purely electrical method of fishing has not 

 yet been developed, but electricity is used in the menhaden catch- 

 ing operation, once the fish have been surrounded by the seine. 

 The anode is placed on the end of the hose used for pumping the 

 fish aboard, and the cathode is laid in the bottom of the net. This 

 brings the fish to the hose, relieves the strain on the net, and 

 speeds up the process. Electricity also is used successfully in 

 fresh water for a variety of scientific purposes, such as sam- 

 pling the fish life of a stream, killing predators like the sea lamp- 

 rey, or guiding salmon past turbines in dams. Electricity, 

 therefore, offers possibilities for locating, for guiding, and for 

 catching fish. If the two operations could be combined, an import- 

 ant step would be achieved in reducing the cost of fishing. One 

 way to do this might be to design an underwater trawler, a sub- 

 marine-like vessel, with open mouth, which would attract fish to 

 itself with electricity, then gulp them in. Such a vessel might 

 even process the fish aboard, bringing a finished product back 

 to shore. 



The needs for instrumentation in FISHERY SCIENCE are 

 many and time will not allow a complete account. (A special 

 list is included in appendix H. ) Better methods to measure 

 abundance in the natural environment would be invaluable, for 

 such information is now obtained quite indirectly by sampling, 

 from tag returns, or from catch statistics. Particularly useful 

 would be practical ways of estimating abundance of young, as a 

 guide for planning future fishing operations, for fluctuations in 

 abundance are sources of difficulty to the fishing industry. They 

 usually are not anticipated, and thus, they add to the cost of 

 fishing. 



When migration pathways are restricted, direct counting 

 maybe possible. In narrow, clear streams, for example, migrat- 

 ing salmon can be counted by eye, but in broad or muddy streams 

 this is difficult or impossible. Electronic counters have proven 

 successful in restricted channels; but in broader streams, much 

 of the width must be blocked in order to lead the fish to the count- 

 er. Barriers interfere with movements of fish in various ways, 

 and may cause serious delays in reaching spawning grounds, to 



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