. Commercial fisheries review. Fisheries; Fish trade. was the principal species sought, many swordfish also were caught. A small per- centage of longline sets was specifically to catch , night fishing with squid as bait, and modification of gear to fish shallower. The catch distribution is thought to be associated with complex subsurface thermal structures. Data from the Pacific coast is insufficient to support or negate this hypothesis. However, surface fish are known to be present off Baja California in June; one was sighted. 43 The Miss Behavior scientists said: "N
. Commercial fisheries review. Fisheries; Fish trade. was the principal species sought, many swordfish also were caught. A small per- centage of longline sets was specifically to catch , night fishing with squid as bait, and modification of gear to fish shallower. The catch distribution is thought to be associated with complex subsurface thermal structures. Data from the Pacific coast is insufficient to support or negate this hypothesis. However, surface fish are known to be present off Baja California in June; one was sighted. 43 The Miss Behavior scientists said: "No explanations can be offered for our failure to encounter subsurface swordfish during our cruise. As far as we know, our effort repre- sents the first time that longline swordfish gear has been used off Baja Calif ornia in the month of ; They add: "A few modifications would greatly increase the efficiency of the opera- tion. Specifically, a larger reel and stand, capable of holding all the , would make it possible to work the gear with a mini- mum of 3 or 4 ; REVERSING A SONAR PRINCIPLE When a piece of iron or other ferromagnetic material is placed in a strong mag- netic field, it is deformed. This principle, called magnetostriction, is used in sonar, where a varying magnetic field causes a transducer to vibrate, causing sound waves in the water. An invention patented recently turns the principle around, and measures force, which causes the iron to change shape, by the change in magnetic field. The output is an electric current, making the device useful for automatic control situations. In the new device, patented by a Swedish inventor, Olof W. Ohlsson, four holes are bored in the ferromagnetic block--two for a magnetizing wire and two for a measuring wire. An electric current in the magnetizing circuit causes a voltage to be induced in the measuring wire; but this measured volt- age depends on the magnetic qualities of the material--its perme
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