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Fishery Bulletin 90(4). 1992 



Dry weight-length relationship 



The dry weight-length relationship for postlarval and 

 juvenile Atlantic bumper (Fig. 6) is described by the 

 exponential model Weight = 0.0016 Length^'-^s (r^ 

 0.94), where weight = dry weight of the fish (mg) and 

 length = standard length (mm). The dry weight-length 

 power term for larval and juvenile Atlantic bumper, 

 3.25, is significantly different from the classical stan- 

 dard length-weight power term of 3.0 for adult fish 

 (LeCren 1951) and 4.0 for larval fish (Power 1989) at 

 the 95% confidence level (p>0.05). 



Mortality 



Instantaneous daily mortality (M) for larval Atlantic 

 bumper was significantly higher during August 1986 

 (F 13.8, p 0.03) than in either September 1986 or 



1987, with September values decreasing during suc- 

 cessive cruises each year (Table 3). As a whole, how- 

 ever, the M values for all cruises in 1986 and 1987 were 

 similar (F 0.74, p 0.45). 



Discussion 



The age of larval and juvenile Atlantic bumper was 

 estimated from counts of growth increments on sagittal 

 otoliths. One growth increment formed daily on each 

 sagitta of Atlantic bumper between 8 and 25mmSL. 

 We, like others (Pritcher 1988, Fowler 1989, Parsons 

 and Peters 1989), assumed that this relationship held 

 true for smaller larvae (1-8 mm). We validated the 

 periodicity of otolith growth increments and estab- 

 lished an otolith age-and-growth analysis for larval 

 Atlantic bumper in the northern Gulf of Mexico. 



Growth increments were not visible in the otoliths 

 of yolksac Atlantic bumper larvae (0.8mmNL), but at 

 least one increment was visible in l.OmmSL larvae. 

 The length at hatching appears to be between 0.7 and 

 0.9mmSL (after preservation) based on the larval 

 length measurements. Atlantic bumper larvae, there- 

 fore, appear to begin otolith increment deposition after 

 yolksac absorption, approximately 2 days after spawn- 

 ing (allowing 1 day each for egg incubation and yolksac 

 absorption). Pelagic species, such as Atlantic bumper, 

 often begin growth increment formation on their 

 sagitta at the time of yolksac absorption (Radtke 1984). 



An isometric or linear relationship between the size 

 of otolith radius and standard length was revealed for 

 Atlantic bumper larvae. The variation observed in our 

 otolith radius-fish size relationship could be influenced 

 by grow^th- and age-related factors. For example, under 

 unfavorable environmental conditions the fish may not 

 continue to experience an increase in otolith radius or 

 fish size, while daily increment formation may continue 

 (Lyczkowski-Shultz etal. 1988, Secor and Dean 1989). 



