The minimum lengths of ripe male and female shovelnose were 523 mm 

 (20.6 in) and 688 mm (27.1 in), respectively, in 1975 and 592 mm (23.3 in) 

 and 743 tin (29.3 in), respectively, in 1976. Other workers have also 

 reported male shovelnose sturgeon maturing at a smaller size than females 

 (Christenson 1975 and Helms 1974). 



Theoretically, a fish should lose weight after spawning. A straight-line 

 relationship of weight at recapture versus weight at tagging would intersect 

 the equilibrium (no weight lost or gained) at the maturity size, providing 

 the fish were tagged prior to spawning and recaptured after spawning. 

 Weights from shovelnose tagged in 1975 (x) were plotted against weights at 

 recapture in 1976 (y) after spawning had occurred. Since only males could 

 be positively identified both years, their weights were plotted (figure 11). 

 The intersection of the growth line and the equilibrium line was at 850 g. 

 Using the length-weight relationship of: 



log w = 3.3439 log fl - 6.2839 



a fork length of 569 mm at maturity was derived for males. This corresponds 

 closely with the 561 mm reported for the Red Cedar and Chippewa river systems 

 of Wisconsin (Christenson 1975). 



POPULATION ESTIMATE 



The estimated numbers of shovelnose sturgeon per kilometer of Tongue 

 River sampled in 1975 and 1976 were similar using all three estimators 

 (table 7). Since confidence interval overlap was evident between estimates 

 of the same year and betv/een different years, the differences do not appear 

 to be significant. The Chapman estimator resulted in the lowest estimate, 

 but also had narrowest confidence intervals. The largest estimate resulted 

 from the Schumacher-Eschmeyer formula. While all requirements for a valid 

 population estimate were not met, the close agreement of the Tongue River 

 estimates suggests a valid estimate. 



TABLE 7. Estimated number of shovelnose sturgeon per km of the Tongue River, 



1975 and 1976. 



^ CI = confidence interval 



34 



