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Fishery Bulletin 97(1), 1999 



perature found by Rutherford and Houde ( 1995) for 

 the Potomac River and Upper Chesapeake Bay and 

 by Secor and Houde ( 1995) for striped bass larvae in 

 the Patuxent River. However, the relationship we 

 found was weak (/•" only 0.15). Some measures of 

 growth were also enhanced with increased food avail- 

 ability. Because of the similarity of our approach with 

 that of these previous Chesapeake researchers, we 

 can compare the fates of striped bass larvae in the 

 Chesapeake and Hudson systems. 



Temperatures during the larval period were more 

 variable in the Chesapeake tributaries in the stud- 

 ies referred to above than in the Hudson in 1994. In 

 the Patuxent in 1991, water temperatures in April 

 (when nearly 90'^ of eggs were produced) fluctuated 

 erratically between approximately 13° and 20°C. In 

 May, temperatures rose through the month from 20° 

 to 29°C (Secor and Houde, 1995). In the Potomac 

 (1987-89) and Upper Bay ( 1988-89) (Rutherford and 

 Houde, 1995), water temperatures also fluctuated, 

 dropping in 1989 during one event from above 16"C 

 to around 12°C, the lower lethal limit for striped bass 

 larvae (Morgan et al., 1981). April and May water 

 temperatures in the Nanticoke, another Chesapeake 

 tributary, also fluctuated in 1992 and 1993 (Kellogg 

 et al.^). In contrast, 1994 water temperatures in the 

 Hudson River increased linearly from mid-April 

 through mid-July with little fluctuation. 



In spite of the overall warmer temperatures, cal- 

 culated instantaneous growth rates of larval striped 

 bass grouped into 6-d cohorts were lower in the 

 Patuxent River (mean instantaneous G=0.126/d. 

 range 0.1 1-0.14) than in the Hudson (mean G=0.190/ 

 d, range 0.070-0.564). Nanticoke River growth rates 

 were intermediate (0.166 in 1992, 0.159 in 1993; 

 Kellogg et al.'^). Hudson striped bass larvae grew at 

 rates similar to those for Potomac River (0.208 and 

 0.181/d for 1987 and 1989) and Upper Chesapeake 

 Bay larvae (0.183/d). In terms of growth in length, 

 both moronid species in the Hudson grew faster than 

 Patuxent River striped bass larvae (Hudson white 

 perch=0.212 mm/d ±0.101 SD, Hudson striped 

 bass=0.218 mm/d ±0.121 SD, Patuxent striped 

 bass=0.17 mm/d for 0-25 d). Note that Dey (1981) 

 estimated Hudson River striped bass larval growth 

 rates (in 1973-76) as ranging from 0.1 to 0.2 mm/d. 



^ Kellogg, L L., E. D. Houde, and D. H. Secor. 1996. Egg pro- 

 duction and environmental factors influencing larval popula- 

 tion dynamics in tlie Nanticoke River, 1992-1993. Chapter 1 in 

 E. D. Houde and U. H. Secor (eds.). Episodic water quality events 

 and striped bass recruitment: lar\',al mark-recapture experi- 

 ments in the Nanticoke River Final Rep. to Maryland Dep. 

 Natural Resources, Chesapeake Bay Research and Monitoring 

 Division. University of Maryland, Ref No. lUMCEESICBL 9(v 

 083. [Available: Chesapeake Biological Laboratory, Box 38, 

 Solomons, MD 20688.! 



based on analysis of weekly changes in mean lengths 

 of larvae. Growth rates in the present study are 

 higher than Day's estimate and fall within the range 

 of the Potomac (mean growth rates 0.18-0.26 mm/d, 

 1987-89; Rutherford and Houde, 1995). Differences 

 in growth rates are likely due to a combination of 

 factors in any given year and site; unfortunately, 

 multiyear studies of larval growth rates, which would 

 provide ranges of variation, are few. 



An index of population growth, Gl Z, has been used 

 as an index of striped bass recruitment success (Ru- 

 therford and Houde, 1995, Secor and Houde, 1995, 

 Rutherford et al., 1997, Kellogg et al.^) in Chesapeake 

 tributaries because the index corresponded, at least 

 on a seasonal basis, with production of 8-mm larvae, 

 which is, in turn, correlated with year-class strength 

 in the Chesapeake system. The GIZ did not corre- 

 late well with our index of recruitment, i.e. juvenile 

 striped bass recruits. We did not examine juvenile 

 recruitment of white perch, nor are we aware of any 

 otolith-based studies of white perch recruitment in 

 other ecosystems. 



The GIZ method as applied at New Hamburg must 

 be viewed cautiously, as calculations of mortality (Z) 

 for individual cohorts are based on a few samples 

 and are not well constrained (hence the large stan- 

 dard errors for some cohorts, Table 2). Further, al- 

 though in aggregate a large number of individuals 

 were examined in this study, growth rates for indi- 

 vidual cohorts were estimated from a limited sample 

 size. Finally, there is likely a substantial variability 

 in time and space for both G and Z that currently 

 exceeds measurement capacity even in the most dili- 

 gent field study. Given these issues of accuracy and 

 precision, our analyses should indicate general 

 trends, but they cannot yet be viewed as conclusive. 



In both the Chesapeake Bay and Hudson River, it 

 appears that lowest mortality rates in striped bass 

 larvae fall within a constrained temperature range. 

 Secor and Houde (1995) found a convex parabolic 

 relationship of Patuxent striped bass mortality rates 

 with temperature; minimum mortality rates were 

 associated with cohorts that experienced water tem- 

 peratures of 16-18°C in the first 25 days of life. Ru- 

 therford and Houde ( 1995) did not find so neat a re- 

 lationship but rather noted that low mortality rates 

 occurred in early May cohorts of Potomac striped bass 

 larvae, which coincided with water temperatures 

 around 16°C. Mortality rates of Hudson River striped 

 bass in 1994 were also lowest in cohorts associated 

 with water temperatures of 16.4° to 18.0°C during 

 the week of hatching (31 May to 5 June, Table 2); 

 however, first feeding by these cohorts also coincided 

 with the zooplankton blooms. White perch mortality 

 rates appeared to decline with increasing temperature. 



