NOTE Fey and Hare: Length correction for larval and early-|uvemle Brevoortia tyrannus 



727 



error. Additionally, decreasing shrinkage as a function 

 of increasing fish length was present when relative (%) 

 shrinkage was analyzed. Similar results with regard 

 to time and fish size effect were previously reported for 

 other fish species preserved with formalin and alcohol 

 (see Fey, 1999, for overview). 



The effect of shrinkage on growth rate analysis was 

 described by Fey (1999) for larval sprat. If growth rate 

 is estimated by using a regression of length at age, the 

 influence of shrinkage on growth estimates depends on 

 the absolute value of length changes (i.e., expressed in 

 mm) among small and large fish, and the error may be 

 as high as 0.07 mm/d. However, if the absolute values 

 of length decrease equally across fish lengths, even 

 large shrinkage (on average) may have no effect on the 

 results of growth rate analysis. In addition to length 

 at age analysis, average growth rate (mm/d) may be 

 calculated for individual fish. The potential error in 

 growth estimates will then be directly proportional to 

 both the relative and absolute magnitude of shrink- 

 age. This potential bias in growth-rate calculations 

 described by Fey (1999) for sprat emphasizes the im- 

 portance of correcting for preservation. Although the 

 relationship between otolith size and fish size may be 

 used for length correction (Leak, 1986; Radtke, 1989). 

 Fey (1999) showed that greater accuracy is provided 

 when a fresh length-preserved length relationship 

 is used. However, such a relationship may be supple- 

 mented by additional measurements (i.e., body depth 

 and otolith size) to improve the accuracy of the correc- 

 tion model (Porter et al.. 2001). In the current study, 

 absolute changes in length (expressed in mm) of alcohol- 

 preserved menhaden were not dependent on fish size 

 and therefore a single correction factor was sufficient 

 for a calculation of live length. The length correction 

 factor provided in our study will benefit future studies 

 on the ecology of early life stages of menhaden, similar 

 to that conducted by Warlen et al. (2002), where pre- 

 served length measurements were used. 



Acknowledgments 



This research was performed while the first author held 

 a National Research Council Research Associateship 

 Award at NOAA Beaufort Laboratory. This note is also 

 a contribution to the State Committee for Scientific 

 Research (grant no. 2P04F 005 27). 



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