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Fishery Bulletin 91(1). 1993 



environment. Further, Atlantic menhaden spawn over 

 a wide range of locations throughout most of the year. 

 This may minimize reproductive failure, because the 

 effects of extreme environmental conditions in one place 

 or time will be dampened by less-extreme environmen- 

 tal conditions in others (Den Boer 1968). 



Differences in life-history characteristics between 

 Atlantic and gulf menhadens observed in this study 

 generally are in agreement with previous studies. Re- 

 ported egg sizes support the observation that Atlantic 

 menhaden eggs are larger than gulf menhaden eggs 

 (Hettler 1984, Powell & Phonlor 1986). The influence 

 of temperature on early-life-history characteristics, in- 

 terspecific differences in size-at-hatching, and size- and 

 age-at-first-feeding are in accord with findings of Powell 

 & Phonlor (1986). An exception was interspecific dif- 

 ferences in growth rate, which were found to differ 

 between species in this study. Interspecific differences 

 between the two menhadens in the wild have been 

 reported by Maillet & Checkley ( 1991 ). Although Powell 

 & Phonlor (1986) found no differences in growth rates 

 between species (growth rates were determined at 20° C 

 only), they found a difference in size at age 21 d past 

 first-feeding (Atlantic menhaden 10.7 mmSL, gulf men- 

 haden 8.9mmSL). This supports observations in the 

 present study that age- and size-at-first-feeding are 

 subtle but important early-life-history characteristics 

 that can influence future size if larvae encounter suit- 

 able prey and temperatures. 



The influence of temperature on hatching size, as 

 observed in this study, has been linked to larval 

 survivorship. Buckley et al. ( 1990) reported that recently- 

 hatched and first-feeding winter flounder Psuedo- 

 pleuronectes americanus larvae were longer and dis- 

 played greater amounts of protein and nucleic acids at 

 low temperatures, thus maximizing size and condition 

 during the cold winter spawning period. Bengston et 

 al. (1987) observed that recently-hatched Atlantic sil- 

 verside Menidia menidia were larger at low tempera- 

 tures. They suggested that this conferred a survival 

 advantage to larvae hatched early in the season (colder 

 temperatures), because they are larger at any given 

 age than those hatched later in the season (warmer 

 temperatures). I was unable to detect a survival ad- 

 vantage in this study. Although gulf and Atlantic men- 

 haden were relatively larger at low incubation tem- 

 peratures (Table 3), incubation temperatures had no 

 influence on size-at-first-feeding. 



Certain early-life-history characteristics do not ap- 

 pear to be correlated with egg size. Egg oil volume, oil 

 utilization rates, oil volume at hatching, and weight- 

 at-first-feeding were not related to egg size (Tables 1- 

 3). Egg oil volume has been correlated with resistance 

 to starvation (Chambers et al. 1989). In the present 



study, there were no differences between menhadens 

 in egg oil volume, and recently-hatched gulf menha- 

 den larvae had a greater volume of oil than Atlantic 

 menhaden, yet still appeared to be least resistant to 

 starvation. This is not surprising, since oil was de- 

 pleted in both species at first feeding. 



A major constraint of this study, and in comparison 

 with previous studies (Hettler 1984, Powell & Phonlor 

 1986), is that adults from all studies were collected 

 from similar areas and may not be representative of 

 the entire population. Intraspecific latitudinal varia- 

 tion in field-collected Atlantic menhaden egg size has 

 been observed in this study, and variation in egg size 

 has been reported for gulf menhaden (Hettler 1984). 

 Evidence in both studies shows that egg size is related 

 to fish size. Hettler (1984) found that larger labora- 

 tory-spawned gulf menhaden (20 cm mean length) pro- 

 duced larger eggs than smaller gulf menhaden ( 18 cm 

 mean length). Because Atlantic menhaden are distrib- 

 uted by size and age, differences in egg size with lati- 

 tude might be related to female size. If so, values for 

 the early-life-history variables (e.g., egg size, size- 

 at-hatching, etc.), especially for Atlantic menhaden as 

 reported here, should be viewed with caution because 

 intraspecific and latitudinal variation in life-history 

 variables was not evaluated in this study. 



With the exception of salmonids, there are few stud- 

 ies that relate interspecific differences in early- 

 life-history traits to the environments that the species 

 occupy. Beacham & Murray (1990) clearly related varia- 

 tion of early-life-history traits of five species of Pacific 

 salmon to their different spawning environments. As 

 in the present study, alevin and fry weight were greatly 

 influenced by egg size. Given the constraints and limi- 

 tations of the present study, the differences in egg 

 size which influenced larval size, along with differ- 

 ences in a suite of developmental events observed be- 

 tween the two menhadens, may reflect life-history se- 

 lection processes that have occurred in their different 

 environments. 



Acknowledgments 



I am grateful to Charles Warren who introduced me to 

 life history theory and its application to fishery sci- 

 ence. Sincere appreciation is extended to William 

 Hettler who captured, transported, and spawned the 

 menhaden, to Curtis Lewis who provided assistance in 

 the rearing of larvae and laboratory experiments, and 

 to Peter Berrien for providing eggs from field collec- 

 tions. Dean Ahrenholz, David Colby, William Hettler, 

 John Merriner, and an anonymous reviewer reviewed 

 the manuscript and made valuable suggestions. This 



