Rutherford and Houde: The influence of temperature on growth of Morone saxatilis 



323 



Potomac 1987 



Potomac 1989 



Potomac 1988 



Upper Bay 1989 



Cohort Hatch Date 



Cohort Hatch Dak' 



□ 



> 



Figure 6 



Cohort-specific, mean growth rates (closed bars, mm-cH) and stage durations (open bars, age (d)) of 8- 

 mm-total-length striped bass, Morone saxatilis, larvae by hatch date in the Potomac River, 1987-89, and 

 Upper Bay 1989. Growth rates determined by the back-calculation method. Error bars indicate 95% 

 confidence intervals. 



days posthatch of surviving larvae collected late in 

 the season were significantly smaller U-test; P<0.001) 

 than lengths at capture of larvae collected earlier, 

 suggesting that within-cohort mortality had acted 

 selectively against larger individuals. There was no 

 significant difference (P>0.50) in mean lengths at age 

 between early and late-captured larvae in the elev- 

 enth cohort. 



Analysis of back-calculated larval growth histories 

 suggested that in most Potomac River and Upper Bay 

 cohorts in each year, small larvae are able to com- 

 pensate for slow initial growth and obtain the same 

 length at >20 days posthatch as larvae with large 

 initial lengths. Lengths at capture were compared 

 with back-calculated growth rates in the period 

 5-20 days posthatch and with calculated lengths at 

 5, 10, 15, and 20 days posthatch. For all cohorts 

 (n=38) in all years, there either was no significant re- 

 lationship between length at capture and their back- 

 calculated lengths at 5 and 10 days posthatch, or the 

 relationship was negative, i.e. within a cohort, some of 

 the smallest-sized larvae at capture had relatively large 

 back-calculated lengths at 5 and 10 days posthatch. 



For individuals hatched early in the spawning sea- 

 son (in 14 of 15 cohorts), there also was no relation- 

 ship between lengths at capture and back-calculated 



lengths at 15 and 20 days posthatch. However, lar- 

 vae that hatched later in the season (in 20 of 23 



0.5 



E 

 £ 



CO 



OS 



o 

 u 



e 

 - 



0.4 - 



G= -0.09 + 0.02T 

 r 2 = 0.67, n = 45 



© 



Potomac River 



u 1987 

 • 1988 

 ° 1989 



Upper Bay 

 ° 1989 



14 16 18 20 22 24 26 



Temperature (°C) 

 Figure 7 



Back-calculated growth rates (G, mm-d" 1 ) of striped bass, 

 Morone saxatilis, larval cohorts, in relation to river tem- 

 peratures (T, °C) averaged over the first 20 days posthatch 

 in the Potomac River, 1987-89, and Upper Bay, 1989. 

 Circled data point is an outlier and was not included in 

 the regression. 



