Powell: Early-life-history traits of Brevoortia tyrannus and B patronus 



125 



Log, Dry Wt.= -2.787 + 5.1 43<log, SL) 

 1-2=0.96 



Log, Dry Wt. : -0.852 *3.357(log, SL) 



02 04 06 08 1.0 1.2 1A 

 LOG, STANDARD LENGTH (mm) 



Figure 6 



Length-weight relationship of larval Brevoortia 

 patronus showing a change in body morphology. 

 Breakpoint occurs at 12mmSL. 



Tilseth 1985 (gadoids), Marsh 1986 (percids), and 

 Goulden et al. 1987 (cladocerans). Relatively larger 

 larvae have been reported to have increased mobility, 

 enhanced encounter rates with prey, and, because of 

 these features, should be better able to detect food 

 (Miller et al. 1988). Large eggs, then, would appear to 

 be more fit in environments where the food supply is 

 relatively poor or variable (Hempel & Blaxter 1967, 

 Goulden et al. 1987). This suggests that the Atlantic 

 menhaden is responding to a more variable or unpre- 

 dictable reproductive environment than its congener. 

 Because larger eggs appear to confer an advantage 

 over smaller eggs, early survival of larvae from larger 

 eggs should be less variable (Miller et al. 1988). This 

 was not apparent in this study. Although growth rate 

 of early Atlantic menhaden was greater than gulf men- 

 haden at moderate to high temperatures (Table 2), the 

 gain in population biomass of larvae did not differ 

 between species (Table 1, Fig. 4). Pepin (1991) also 

 was unable to support the prediction that larval sur- 

 vival is less variable for species that spawn large eggs. 

 The cumulative effects of egg size through the early- 

 larval stage may influence menhaden stage duration. 

 Atlantic menhaden not only produce larger eggs and 



larger larvae at the onset of feeding than do gulf men- 

 haden, but they also have higher rates of yolk utiliza- 

 tion and, apparently, higher rates of development (i.e., 

 digestive and sensory systems). Hence, Atlantic men- 

 haden larvae are not only larger, but also younger, 

 than gulf menhaden at first-feeding. This could result 

 in larger larval size shortly after first-feeding (e.g., 

 10 d), if larvae encounter suitable prey and tempera- 

 tures. Moreover, Atlantic menhaden appear to undergo 

 transformation of development (based on the relation- 

 ship between length and weight) at a relatively smaller 

 size, thus spending relatively less time in the early- 

 larval stage. Chambers et al. (1988) showed that win- 

 ter flounder Psuedopleuronectes americanus larvae that 

 metamorphosed early were growing faster than their 

 cohorts despite their small size at metamorphosis. Fur- 

 thermore, the size advantage acquired during the lar- 

 val period was maintained during the early-juvenile 

 period. Williams (1966) argued that acceleration of de- 

 velopment will occur in those developmental stages in 

 which mortality rates are high. Comparatively, Atlan- 

 tic menhaden reproduce in an environment that is un- 

 predictable, and the suite of traits exhibited by this 

 menhaden species mediates the unpredictability of the 



