NICHOLSON and SCHAAF: AGING OF GULF MENHADEN 



would be expected. Those at the time of the second 

 ring formation, whether calculated from fish with 

 only a ring in the second position or from fish with 

 both rings, were nearly identical and were shifted 

 slightly to the right of distributions calculated 

 from fish with three rings. 



CONCLUSIONS 



On scales of most Gulf menhaden with one or 

 two rings, the rings appear to be true annuli. A 

 relatively large number of fish that do not form a 

 ring at the end of the first year form a ring at the 

 end of the second year. A very small number that 

 form a ring at the end of the first year do not form a 

 ring at the end of the second year. It is possible, 

 therefore, to separate age-2 from age-1 fish by the 

 number of rings, or the location of the ring if only 

 one is visible. 



For fish having scales with more than two rings, 

 or with two rings that are oddly spaced, it is 

 difficult to differentiate between true and false 

 annuli, or to determine to what year a particular 

 ring should be assigned. On scales of some fish that 

 could be age 3 on the basis of length, only two rings 

 are visible, in what appears to be either the first 

 and second or second and third positions. On some 

 scales that have three well-defined rings, the spac- 

 ing appears too unusual to be true annuli. For 

 those fish that are called age 3, the lengths overlap 

 those of age-2 fish, the mean lengths and ranges 

 progress very little during the season, and the 

 mean increments from the last annulus to the 

 scale edge show little increase. We concluded that 

 it is impossible to separate age-3 from age-2 fish 

 with a high degree of certainty on the basis of the 

 number or the location of scale rings. 



From late August until October a small number 

 offish ranging from about 115 to 135 mm appear. 

 We believe most of these fish, which have no scale 

 rings, are age 0, but we cannot be certain because 

 many of the fish in this size range of age-1 fish also 

 have no scale rings. 



The small number of tags recovered after 2 yr 

 from fish tagged as juveniles, or age 0, the scarcity 

 in the catch of fish larger than those with two 

 rings, and the small numbers of fish with more 

 than two rings, indicate that few Gulf menhaden 

 live to be older than age 2. Since both age-0 and 

 age-3 fish compose <2'Jc of the catch, and since 

 each age-group is either impossible or difficult to 

 identify, we believe it is practical to recognize only 



two age-groups of Gulf menhaden: those age 1 or 

 younger and those age 2 or older. 



If only two ages are recognized, fish with no 

 annuli can be aged by length. For each month, 

 those below a certain fork length can be called age 

 1 or under, those above a certain length age 2 or 

 older. Those in between cannot be individually 

 aged, but the number in each length class can be 

 apportioned to each age-group on the basis of the 

 percentage offish in each length class with one or 

 two annuli. For example, in June 197 1 (Table 3) all 

 fish <165 mm may be called age 1, all >185 mm 

 age2. Ofthe31unagedfishl65-169mm,30(97%) 

 are age 1 and 1 (3%) is age 2; of the 45 between 170 

 and 174 mm, 37 (82%) are age 1 and 8 (18%) are 

 age 2. 



A question that may arise concerns the accuracy 

 of previous aging methods. To shed some light on 

 this question, we compared the percentages offish 

 at each age for methods 1 and 2. In method 1, fish 

 ages had been based on a combination of factors: 

 the general appearance of the scales, the number 

 and location of rings, the fish length, and the time 

 of year the fish was caught. In method 2, fish that 

 had been aged by the number and location of scale 

 rings, and fish that could not be aged, were 

 grouped in 5-mm size classes. For each size class 

 the number of unaged fish were apportioned to 

 each age-group by the same percentage as fish that 

 had been aged. We retained the age-3 group for 

 comparative purposes, but could not differentiate 

 between age-0 and age-1 fish. 



The percentages at each age were remarkably 

 similar, the differences between methods varying 

 from only 0.1 to 2.7%. We concluded, therefore, 

 that age compositions based on the previous 

 method of aging are reliable and that valid infer- 

 ences pertaining to population dynamics of Gulf 

 menhaden can be based on them. 



LITERATURE CITED 



FORE, P. L., AND K. N. BAXTER. 



1972. Diel fluctuations in the catch of larval Gulf men- 

 haden, Brevoortia patronus, at Galveston entrance, Tex- 

 as. Trans. Am. Fish. Soc. 101:729-732. 



KROGER, R. L., AND P. J. PRIST AS. 



1975. Movements of tagged juvenile menhaden (Brevoor- 

 tia patronus I in the Gulf of Mexico. Tex. J. Sci., 26:473- 

 477. 



Parker, R. O., Jr. 



1973. Menhaden tagging and recovery: Part II — Recovery 

 of internal ferromagnetic tags used to mark menhaden, 

 genus Brevoortia. Mar. Fish. Rev. 35(5-6):36-39. 



321 



