transform into the adult form (Reintjes 1970). The 

 following autumn the juveniles, ranging in fork 

 length from about 55 to 130 mm FL, migrate from 

 the estuaries to offshore waters (Tagatz and Wil- 

 kens 1973), along with all other age-groups that 

 are moving from inshore waters of the gulf at this 

 time. Fish of all age-groups migrate to inshore 

 waters again the following spring. 



While in inshore waters, age 1 and older Gulf 

 menhaden are subject to an intensive purse seine 

 fishery that extends from Florida to eastern Texas 

 from about mid- April to early October. The fish are 

 processed into meal, oil, and solubles at plants in 

 Mississippi and Louisiana. 



During the purse seine season Gulf menhaden 

 are sexually inactive. Therefore, gonads collected 

 at that time are of no use for fecundity studies. The 

 only source of Gulf menhaden during the spawn- 

 ing season is the offshore groundfish trawl fishery, 

 which takes Gulf menhaden incidentally along 

 with the primary species. Catches are landed at 

 plants in Mississippi and Louisiana and processed 

 as canned pet food (Roithmayr 1965). The number 

 of Gulf menhaden taken varies, but is never large. 

 From October 1976 to February 1977, 241 females 

 (124-257 mm FL) and 516 males (113-240 mm FL) 

 were collected from the groundfish landings. After 

 January, we were able to collect only 4 maturing 

 females in February and none in March or April. 



To assure that Atlantic menhaden, B. tyrannus, 

 were assigned to the correct year class, June and 

 Reintjes (1959) developed specific criteria for as- 

 signing fish to year classes on the basis of annulus 

 formation. These criteria also were adopted when 

 the investigation of Gulf menhaden was begun in 

 1964. March 1 was designated as an arbitrary date 

 on which all fish of a given year class were ad- 

 vanced 1 yr in age, regardless of whether or not a 

 new annulus had formed. Since all fish used in this 

 study were collected from October to February, 

 an age-1 fish is one that has one annulus, but 

 has completed two growing seasons; an age-2 fish 

 has two annuli but has completed three growing 

 seasons. 



All fish were caught in the northern Gulf of 

 Mexico from lat. 28°35 ' to 30°15 ' N and from long. 

 87°45 ' to 9r28 'W. Fork lengths were measured to 

 the nearest millimeter and wet weights to the 

 nearest 0.1 g. Scale samples for aging were taken 

 from the left side of the body along the midline and 

 below the origin of the dorsal fin. Paired gonads 

 were preserved in a 10% buffered Formalin^ solu- 

 tion. 



Stages of Sexual Maturity 



Preserved gonads were blotted to remove excess 

 moisture and weighed to the nearest 0.01 g. A 

 sample of 0.1 g or less was cut from the central 

 portion of an ovary and examined microscopically 

 to describe morphology of developing ova and to 

 determine the mean diameter of the largest ova 

 present. 



Four groups of ova were found in the most ad- 

 vanced ovaries, while only one to three groups 

 were found in less developed ovaries. Immature 

 ova were under 0.20 mm in diameter, translucent, 

 and contained an irregular spherical nucleus. In- 

 termediate ova ranged from 0.20 to 0.35 mm and 

 had a dark or opaque center surrounded by a wide 

 sphere of dull yellowish to brownish speckling. 

 Maturing ova were 0.36 to 0.72 mm, opaque, and 

 had an outer translucent covering or tissue. Ripe 

 ova were similar to maturing ova except they were 

 >0.72 mm. 



Three stages of sexual maturity were recognized 

 on the basis of the most advanced group of ova 

 present: immature, intermediate, and maturing. 

 Fish classified as maturing contained either 

 maturing or both maturing and ripe ova. All 

 maturing or ripe ova in a sample were counted and 

 about 100 were selected randomly and measured 

 for diameter. 



Age and Size of First Spawning 



Gulf menhaden <135 mm can be considered as 

 age-0 fish (Nicholson and Schaaf 1978). All fish 

 <100 mm FL that we examined showed no evi- 

 dence of maturing ova. Through December, 63% of 

 age-1 fish and 71% of all fish age 2 or older in our 

 samples contained maturing ova. By January all 

 fish age 1 or older contained maturing ova (Table 



^Reference to trade name does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



Table l. — Number of female Gulf menhaden sampled from Oc- 

 tober 1976 to February 1977 by age, month, and stage of sexual 

 maturity (immature or mature). 



' Flsti with Intermediate ova (as ttie largest ova present) were included in ttiis 

 category. 



948 



