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Fishery Bulletin 98(2) 



partial temporal or spatial coverage, or 

 both, fall within the temporal limits that 

 we detected (de Ciechomski, 1968; Hubold 

 and Ehrlich, 1981; Cassia and Booman, 

 1985; Lasta and de Ciechomski, 1988). 



Brevoortia aurea eggs remain in the 

 bottom layer of the water column, near 

 where the halocline intersects the bottom 

 (Fig. 3). At this frontal interface, a conver- 

 gent flow near the bottom (Largier, 1993) 

 would serve to retain eggs near the con- 

 fluence of river and marine waters, mini- 

 mizing their drift. Thus, specific gravity of 

 the eggs seems to be an important feature 

 of the reproductive strategy of B. aurea, 

 allowing the eggs to stay in the saltier ( and 

 denser) bottom waters. Typically, bottom 

 waters move landward in salt-wedge estu- 

 aries (Kjerfve, 1989; Mann and Lazier, 

 1991 ). Lower egg concentrations in the rest 

 of the estuary probably indicate some dis- 

 persion of eggs or reduced spawning in 

 these areas. 



Disruptive events such as storms, which 

 destroy the halocline (Guerrero et al., 

 1997a), intermittently occur in this region. 

 These meteorological events are character- 

 ized by strong winds over 13 m/s from the 

 southeast (Balay, 1961). The events have 

 a characteristic duration of 1-3 (occasion- 

 ally 5) days, occur throughout the year, and are usu- 

 ally the strongest from May to October (Anonymous, 

 1995). During these events, the estuarine circulation 

 is modified, thus altering the egg retention properties 

 of the system as well. The protracted reproductive 

 season and multiple spawning of B. aurea (Macchi 

 and Acha, 2000) may help to ensure that enough eggs 

 survive in this unpredictable environment. 



The four menhaden species in the Northern Hemi- 

 sphere are the small-scaled menhaden B. smithi and 

 B. gunteri and the large-scaled menhaden B. tyran- 

 nus and B. patronus (Ahrenholz, 1991). Thei-e is little 

 information on the biology of 6. smithi and B. gunteri. 

 Conversely, B. tyraruius and B. patronus have been 

 intensively studied, and the information on their life 

 histories has been broadly reviewed (Ahrenholz, 1991; 

 Powell, 1994). Both species have protracted reproduc- 

 tive seasons and a main spawning period in winter 

 (Nelson et al, 1977; Shaw et al., 1985; Powell, 1994). 

 Spawning of these menhaden takes place in marine 

 waters. Larvae swim and drift with tides and currents 

 toward estuaries where metamorphosis from larvae 

 to juveniles takes place. In the case of B. tyrannus. 

 larvae must be transported from the intensive spawn- 

 ing area south of Cape Hatteras, up to 100 km to 



estuarine nursery areas (Warlen, 1992; Powell, 1994). 

 Brevoortia patronus seems to spawn relatively close 

 to estuarine nursery areas (Shaw et al., 1985). 



Brevoortia aurea, B. tyrannus. and B. patronus all 

 have protracted spawning periods. The southern spe- 

 cies is a spring-summer spawner; the northern ones 

 spawn during cooler months. In the case of 6. tyran- 

 nus. however, adults search for temperatures >17°C to 

 spawn, and as larvae are transported nearer the coast, 

 they enter cooler water (Warlen, 1992). Notwithstand- 

 ing, the reproductive thermal range of the northern 

 species (12.9-21.2 C for B. patronus, and >17€ for 

 B. tyrannus (Warien, 1988; 1992) lies close to that of 

 B. aurea. The proposed advantage of winter spawn- 

 ing refers to maximum onshore transport during that 

 season, providing a mechanism for transporting larvae 

 of both species into the vicinity of estuaries (Nelson et 

 al, 1977; Warlen, 1988). 



The main differences between B. aurea and those 

 northern menhaden seem to be the population bio- 

 mass and the spawning habitat. Brevoortia tyrannus 

 and B. patronus exhibit large population sizes and 

 are a significant component of United States fishery 

 landings (Vaughan, 1991; Powell, 1994). Although 

 there is no biomass assessment for B. aurea, it has 



