SHEPHERD and GRIMES: REPRODUCTION OF WEAKFISH 



enough spent weakfish ovaries to determine if this 

 phenomenon was consistent from year to year. 



The variable reproductive and age and growth 

 characteristics for weakfish in different geo- 

 graphic areas suggest specific physiological re- 

 sponses to different environmental conditions. 

 North Carolina weakfish had smaller sizes at 

 maturity, smaller length at corresponding age 

 after age 1, reduced longevity and maximum size, 

 and higher relative fecundity than New York 

 Bight weakfish. However, the lifetime reproduc- 

 tive potential was nearly equal for both groups. 

 These life history characteristics for weakfish are 

 similar to clinal variations between Labrador 

 and Florida described for American shad (Leggett 

 and Carscadden 1978), differences in reproductive 

 characteristics between Atlantic herring, Clupea 

 harengus harengus, in the Norway and the Baltic 

 Sea (Schopka 1971), and north to south variations 

 in North American populations of Pacific herring, 

 Clupea harengus pallasi (Paulson and Smith 

 1977). 



The different reproductive strategies in 

 weakfish may result from varying environmental 

 demands. When weakfish spawning occurs in 

 northern estuaries, water temperatures are un- 

 predictable and subject to sudden drops which are 

 potentially lethal to eggs and larvae (Harmic 

 1958). Table 6 shows minimum estuarine temper- 



TABLE 6. — Surface water temperatures (°C) 

 for April-July in Plum Island, N.Y.; Cape 

 May, N.J.; Gloucester Point, Va; and Beaufort, 



N.C. 1 



'National Ocean Survey 1972 Surface water 

 temperature and density; Atlantic coast, North and 

 South America. 4th ed NOS Publ .31-1, p. 1-109. 



atures during the spawning season in northern 

 waters may drop below the temperature limits of 

 12°-16°C necessary for successful hatching (Har- 

 mic 1958). The higher probability of prereproduc- 

 tive mortality of progeny in northern estuaries 

 results in a "bet-hedging" strategy in which fewer 

 eggs are produced each year, but the possible 

 number of annual spawnings are increased 

 (Stearns 1976; Giesel 1976), thus maximizing po- 

 tential contributions to the gene pool throughout a 

 fish's lifespan. In contrast, southern weakfish 

 spawn in a more predictable estuarine environ- 

 ment (Table 4) and, consequently, there is less 

 chance of environmentally induced prereproduc- 

 tive mortality. However, southern fish are faced 

 with greater postreproductive mortality (longev- 

 ity observed by Merriner (1973) was 5 yr). Greatest 

 reproductive success in this situation requires 

 maximizing annual gamete production in the few 

 years possible. In addition, weakfish migrating to 

 northern estuaries (Nesbit 1954) may utilize 

 energy reserves otherwise available for gonad 

 growth, whereas southern fish having less dis- 

 tance to travel may reallocate energy towards re- 

 production. 



Consequences of the area specific reproductive 

 characteristics may be a reduced population sta- 

 bility for weakfish in the northern end of the 

 range. Apparently, northern fish have a strategy 

 to cope with potentially higher egg and larval 

 mortality by spreading reproduction over more 

 years and reducing annual fecundity, i.e., a "bet- 

 hedging" strategy (Stearns 1976). Therefore, to 

 fulfill their reproductive potential they must avoid 

 premature adult mortality. If adult mortality 

 (natural and fishing) in weakfish becomes exces- 

 sive, the larger, most fecund individuals will be 

 lost or reduced, thus shifting the burden of spawn- 

 ing to the smaller, less fecund fish. When the value 

 of b in the fecundity equation F = aTL b is >3, as in 

 New York Bight weakfish, then truncation of the 

 size/age structure in a spawning population will 

 also result in a reduction of population fecundity 

 (Hempel 1979). Concurrent high adult mortality 

 and high prereproductive mortality could contrib- 

 ute to a decline in population abundance. The 

 large fluctuations which have occurred in 

 weakfish populations over the last several decades 

 (Wilk 1979) may be due in part to these cir- 

 cumstances (i.e., high adult and prereproductive 

 mortality). Although the correlation between 

 population fecundities and recruitment is not 

 usually strong for marine fishes (Cushing 1977), a 

 decrease in population fecundity may eventually 



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