rate of 57 mm for eels 270-500 mm long over the 

 2-yr studied (95% C.I. [confidence interval] = 

 ± 8.4 mm, growth periods treated as independent 

 random variables, Bliss 1967). Growth as percent 

 increase in length for an average eel 347 mm long 

 was 16%. 



Accuracy of the extrapolated annual estimate 

 can be tested against independent, long-term 

 growth data from animals whose recapture inter- 

 vals included both growth periods. Seven animals 

 had recapture intervals of 6-16 mo (Table 2); 

 average growth was 62 mm/yr (95% C.I. = ± 20.1 

 mm) or a 17% increase in length. 



TABLE 2. — Annual growth rates of eels in Fridaycap Creek, Ga., 

 based on long-term recaptures. Data are from eels that were at 

 large for more than a 180-d interval that included both fast and 

 slow growth periods. 



'Eel No. 1 was captured four times; growth between first and third and be- 

 tween second and fourth captures were analyzed separately. 



When the data are grouped into 50 mm size 

 classes, animals in the 350-400 mm class grew 

 faster than smaller animals (Fig. 1); 95% confi- 

 dence intervals for other size classes overlapped, 

 although some overlap may result from small 

 samples of larger animals. Similar trends in 

 relative growth (percent increase in length) were 

 apparent (Fig. 1): values overlapped in the 

 smaller size classes, and the largest size class grew 

 slower than the fast-growing 350-400 mm group. 



Growth rates during fast growth periods (Table 

 1) suggest that animals grew faster in 1982 than in 

 1981 ( t-test, one tail, df = 76, P < 0.05). Maximum 

 growth rates also differed: the 5 fastest growth 

 rates, as well as 13 of the 15 fastest rates, occurred 

 in 1982 (Table 1). 



Information on weight gain is less complete but 

 shows a similar seasonal trend. Average weight 

 increase between recaptures was 0.223 g/d (SD = 

 0.222, N = 47) for the fast growth period; limited 

 data suggest lesser gains for the slow growth 

 period (0.017-0.144 g/d, A7 = 2). When seasonal 

 data are summed and a 4-mo slow growth period 



is assumed, annual weight increase was 63 g. 

 Long-term weight change data from two animals 

 at large 299 and 371 d indicate an average weight 

 increase of 76 g/yr (range = 67 to 86 g/yr). 

 Mean lengths at different ages were 



Age class (yr): II III IV 



V 



VI VII 



x length (mm) 242 310 361 403 442 460 



Range (mm) 197- 214- 233- 256- 297- 386- 



278 446 548 570 559 500 



N 6 51 134 78 32 5 



The mean values project an average annual in- 

 crease of 44 mm (range = 39-68 mm). The related 

 length-age regression for all eels aged at this 

 locale during the study period was length = 183.3 

 + 43.5 x age (N = 305, r = 0.492, P < 0.01) 

 which also projects an average annual increase of 

 44 mm (95% C.I. = ± 8.7 mm) for an average eel 

 370 mm long. 



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LENGTH CLASS (mm) 



FIGURE 1. — Growth rates of recaptured American eels as a 

 function of size at initial capture, Fridaycap Creek, Ga., October 

 1980-November 1982. Growth is expressed as the actual daily 

 rate of increase (solid vertical lines, means ±95% confidence 

 intervals) and the percent increase as a function of initial length 

 (dashed vertical lines, means ± 95% confidence intervals). Data 

 are from fast growth periods, 1981 and 1982 combined. Numbers 

 beside each mean are the total animals comprising each 50 mm 

 size class. Midpoints of length classes are shown on x-axis. 



520 



