Webb and Kneib: Individual growth rates and movement of Litopenaeus setiferus in a tidal marsh nursery 



383 



Oct 



(39) 



Nov 

 (15) 



Month 



Figure 4 



Mean daily specific growth rates and mean initial size of 

 marked and recaptured juvenile white shrimp by month. 

 Only individuals at large for 3 to 32 days were included. 

 Error bars are 2 SEs and the number of observations are 

 given in parentheses below each month. 



intertidal (Fig. 5A) than there was between growth and 

 mean initial size (Fig. 5B) at the landscape level. There 

 was almost no correlation between proportion of drainage 

 area that was intertidal and initial mean size of marked 

 shrimp (Pearson r=-0.18, P=1.0). 



Residence time and movement of marked shrimp 



Recaptured shrimp were at large for up to 99 days, but 

 mean residence time for individuals marked in all four 

 tidal creeks was between 15 and 26 days (Fig. 6). Mean 

 residence time was greatest at EF and least at SC. During 

 their time-at-large, net displacement (distance between 

 mark and recapture sites) of the marked individuals 

 ranged from to 3000 m , but averaged 258-373 m in all 

 creeks. There was no evidence of a significant relationship 

 between time-at-large and mean net displacement (linear 

 regression F=1.48; df=l,45; P=0.23), but movement was 

 slightly related to shrimp size, and larger individuals 

 showed greater displacement (Fig. 7). Variation in resi- 

 dence time among creek subsystems was not significantly 



correlated with length of the creek mainstem (Pearson 

 r=-0.32, P=0.684), but there was evidence of positive 

 associations with the amount of intertidal (Pearson 

 r=0.87, P=0.133) and subtidal (Pearson r=0.95, P=0.054) 

 drainage areas within each subsystem. 



Most shrimp (939r) were recaptured in the same tidal 

 creek subsystem in which they were originally marked, 

 but there was some evidence of movement among creeks 

 and between the subtidal and intertidal components of 

 the shrimp nursery within creeks. The marked individual 

 at large for the longest time (99 days) was recaptured 

 at the same station where it was originally marked (net 



