CTFM SONAR 



The Continuous Transmission Frequency Modu- 

 lated sonar wliicli was installed in the AVR several years 

 ago has now been evaluated by F.J. Hester. We had 

 hoped that this type of sonar, developed for BCF, would 

 enable a tuna boat to follow the very rapidly moving 

 schools which are so difficult to follow with a conven- 

 tional pulsed sonar. We had also hoped that the size of 

 the fish in a school could be estimated, so as to prevent 

 the contravention of regulations concerning the size of 

 tuna which may be landed, and the enclosing of fish small 

 enough to gill themselves in the meshes of the net. 



The CTFM sonar was coupled with a high-resolution 

 frequency analyzer to analyze Doppler shifts caused by 

 motions and by body flexure of target fish. Targets 

 showing complex, broad-band Doppler shift were found 

 to be characteristic of fish schools. Interspecific varia- 

 tions in these broad-band Doppler patterns were found 

 between small fish schools and single large tuna. 



Unfortunately, Hester found some unforseen and 

 intractable problems in the use of this sonar as a tactical 

 tool ; at ranges of several hundred meters, very good con- 

 tact can be maintained with schools of tuna, but they 

 have a frustrating habit of fading from contact. Tliis 

 disappearance has been traced to small changes in the 

 lateral orientation of the fish in respect to the sonar 

 beam; only when the long axis of the fish is normal to 

 the sonar beam can fish be detected at long ranges. The 



same problem does not apply to contact made with 

 schools of clupeids at the same ranges, perhaps because 

 of their small internal intervals; for such fish the rapid 

 scan rate of the CTFM sonar made it possible to estimate 

 school size and movement at any instant. 



We do not expect, therefore, that CTFM sonar will 

 be applicable to commercial tuna operations as a tactical 

 tool, but it clearly has a place in the sonar array of a 

 fishery research vessel. 



LOCAL FISHERY SYSTEMS DEVELOPMENT 



During the course of other work it is inevitable 

 that fishery problems of purely local interest should pre- 

 sent themselves to the attention of the Operations Re- 

 search Program. These questions are pursued where their 

 solution seems likely to give an immediate economic re- 

 turn and work on them does not conflict with the plans 

 of work of State laboratories. 



S. Kato completed his work on the sharks assoc- 

 ciated with the eastern tropical Pacific tuna fisheries. He 

 has turned his attention to the latent basking shark re- 

 source off California, which had not been fished since 

 1950 when it became uneconomic because of the start 

 of industrial synthesis of vitamins previously extracted 

 from shark liver oil. 



Fishing operations research -small sword fish vessel e- 

 quipped with harpoon gear, now turning to basking shark 

 fishery in offseason. 



S. Kdto 



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