Leffler and Shaw: Age, growth, and mortality of larval Chloroscombrus chrysurus 



715 



C Y = 1 20 -f 05X, R =0 77 



E ' N = 160 



c 



c 



10 20 30 40 50 60 70 



Otolith Radius (microns) 



Figure 5 



Regression of larval standard length (mm) on sagittal 

 otolith radius (^i) for Atlantic bumper Chloi-oscombrus 

 chi-ysiu-us lai-vae collected off the Louisiana-Mississippi 

 barrier islands, 1986-87. 



collections. Comparisons of the growth curves for 

 September 1986 and 1987 and August 1986 indicated 

 a significant difference in both the August intercept 

 (p<0.04) and slope (p<0.03) of the regressions. Even 

 though the sample size (A'^ 9) was small, the observed 

 growth rate for August (0.40 mm/day) was significantly 

 higher than for September (0.26 mm/day in 1986 and 

 0.31 mm/day in 1987). The higher August growth rate 

 occurred at a higher mean surface-water temperature, 

 29.6°C (Table 1). In September of 1987, the water 

 temperature range (26.5-30.0°C) was wider than the 

 other sampling periods due to a cold front passing 

 through before the late-September cruise. There was, 

 however, no significant difference (/:» 0.11) in temper- 

 ature between months because of the low number of 

 cruises. 



Atlantic bumper standard lengths were regressed on 

 the otolith radius (measured in microns; Fig. 5). The 

 coefficient of determination (r^) for the relationship 



Table 2 



Zooplankton standing-stock estimates (mL/nr'±SE) with 

 1987 values converted to equivalent 202 fim mesh net values, 

 based on the conversion study done during both September 

 cruises in 1987. The number of samples taken during each 

 cioiise is indicated in parentheses. The following equation was 

 used in the conversion: Y = 0.785X - 0.054 {R- 0.86). 



1986 



1987 



Month 



(202 ^m) 



Converted 



(333 Mm) 



August 

 early Sept. 

 late Sept, 



0.83±0.17 



(34) 

 0.61±0.13 



(25) 

 0.32 ±0.05 



(41) 



0.57 ±0.04 



(40) 

 0.39 ±0.03 



(40) 



0.39 ±0.04 



(40) 

 0.25 ±0.03 



(40) 



was 0.77 and the equation is L = 120 -i- 0.05R, where 

 L = standard larval length (mm) at the otolith radius, 

 R (Fig. 5). The relationship between the age and otolith 

 radius explained less variability (r^ 0.68) and fit the 

 following equation A = 2.96 -i- 0.13R, where A = age 

 in days at the otolith radius, R. Otolith radius was 

 observed to increase with both larval length and age. 



Zooplankton blomass 



Zooplankton mean biomass values for 1986 were sim- 

 ilar to the converted 1987 values. The 202 vs. 333/um 

 mesh regression equation Y = -0.054 -i- 0.785X 

 {r~ 0.86), where Y = the 333 f^m zooplankton stand- 

 ing-stock value, and X = the 202 ^^m zooplankton value, 

 was used to establish a correction factor to convert the 

 1987 zooplankton values into estimates comparable to 

 the 1986 values. The highest mean zooplankton bio- 

 mass estimate (0.83 mL/m^) was found in August 1986 

 (Table 2). The mean standing-stock estimates declined 

 throughout the September cruises within each year 

 (Table 2). 



