FISHERY BULLETIN; VOL. 76, NO. 2 



Our primary objective was to determine if rings 

 visible on some scales w^ere true annuli. If they 

 were, our second objective was to determine if fish 

 that had scales with no visible rings or with a 

 profusion of unclear rings could be aged on the 

 basis of length; if the rings were not annuli, our 

 second objective was to explore other methods of 

 aging Gulf menhaden. 



COLLECTION OF DATA 



Samples of the catch are taken daily by field 

 personnel stationed at four ports, each comprising 

 two or three plants grouped in close proximity. 

 After weighing and measuring a fish, samplers 

 remove a cluster of scales from just above the lat- 

 eral line below the dorsal fin and deposit them in a 

 0.1% phenol solution. Later, six scales from each 

 fish are cleaned and mounted between two glass 

 slides. Each fish and its scales are identified by 

 port, collection, and scale number. From 1964 to 

 1971, two samples of 20 fish each were taken daily 

 at each port. Since 1972, three samples of 10 fish 

 each have been taken. 



Juveniles ranging from about 80 to 120 mm FL 

 were marked in late summer and early autumn 

 with numbered internal ferro magnetic tags simi- 

 lar to, but smaller than, those used for adults 

 (Pristas and Willis 1973). Tags were recovered on 

 magnets in various parts of the processing plants 

 (Parker 1973), although all tags passing through a 

 plant were not retained. 



To estimate the numbers of field tags not re- 

 tained on magnets, batches of 100 fish marked 

 with test tags were periodically planted in the 

 catches. The percentage subsequently recovered 

 was an estimate of the efficiency of the magents to 

 recover field tags. The number of annual tests at 

 each plant varied from 2 to 15 (200-1,500 tags). 

 Annual recovery rates varied from 2 to 60% , but 

 over one-half were between 15 and 40%. 



Some test tags were not recovered until 1, 2, or 

 even 3 yr after they had been placed in catches 

 (Table 1). Delayed recoveries were caused by 1) 

 tags lodging in various parts of a plant before later 

 being dislodged, 2) tags remaining in fish scrap 

 stored for long periods before being ground, 3) tags 

 remaining in various scrap storage areas before 

 being mixed with new scrap. The number varied 

 by plant and year and amounted to about 1% or 

 less of the number of test tags applied, although in 

 1972 it was 6% at plant 58 and 5% at plant 57. 



Table l. — Number of test tags applied and number recovered at 

 Gulf menhaden processing plants, 1971-73. 



OBSERVATION OF SCALES 



Scales were viewed on a scale projector at 48 x 

 magnification. If no rings were evident, or if no one 

 ring could be considered as an annulus, no mea- 

 surements were made. If rings were evident, the 

 distances from the focus to each ring and to the 

 scale edge of the projected image were measured. 

 Each ring had to be discernable on three or more 

 scales or it was not measured. Each fish was as- 

 signed an age corresponding to the number of 

 rings on the scales except when the only ring visi- 

 ble was in the area of the scale usually occupied by 

 the second ring. Then the fish was called age 2 

 rather than age 1. The decision to assign a ring the 

 number one or two position was based on the dis- 

 tance of the ring from the scale focus. 



VALIDITY OF RINGS AS 

 YEAR MARKS 



To determine if observed rings were true annuli, 

 we examined three different sets of data: length- 



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