Figure 2. — Closed gate forcing fish off conveyor belt into a tub. 



menhaden fishermen, however, often remain at 

 sea for several days fishing over a wide geograph- 

 ical area. Hence, our electronic detector-recovery 

 system adapted for operation aboard fishing ves- 

 sels was thought to be the best means of ob- 

 taining reliable menhaden migration data in the 

 Gulf. We have not yet resolved the technical 

 jn-oblems of application of this system to use on 

 vessels. The major problem is not detection of 

 tagged fish as they are pumped aboard, but re- 

 trieval of the fish once it has been detected. 

 Results from tags recovered by magnets in the 

 Gulf now indicate that reliable estimates of the 

 interchange of fish between fishing areas, growth 

 and mortality rates, and the importance of cer- 

 tain estuaries in the production of menhaden may 

 be obtained from these data. Thus, it may not 



now be necessary to adapt the detector-recovery 

 system for operation aboard fishing vessels. 



RECOVERIES 



Since we began using the detector-recovery 

 system in the summer of 1967, we have recap- 

 tured 2.31 fish. Only 34 recaptures had been 

 out 4 months or longer and just two of these, 

 both females, had been measured and scale sam- 

 pled when released. One female, out 130 days, 

 moved from Chesapeake Bay to North Carolina 

 during the fall spawning migration. She grew 

 13 mm, 290 to 303 mm (fork length), or an av- 

 erage of 3.1 mm per month. The other female 

 was released and recaptured in North Carolina 

 waters. She had been out 483 days, from the 



