were 17.9°C (64.2°F) and 17.7°C (63.9°F), respectively (figure 18). Maximum 

 temperatures were 21.20C (70.2OF) and 21.5°C (71.70F), respectively. 



Therefore, the optimum temperature range for spawning of shovelnose 

 sturgeon is between I6.9OC (62.50F) and 21.50C (70.7OF). The majority of 

 the sturgeon were captured at temperatures from 18. 9^0 (66°F) to 25.60C 

 (78°F). Brown (1971) stated that shovelnose sturgeon spawn in Montana at 

 temperatures between 15.6°C (6OOF) and 21.70c (70OF). This corresponds 

 closely with the temperatures found in the Tongue River. In the Powder 

 River the peak of the shovelnose sturgeon run occurred at 16°C (60.8°F); 

 however, these fish were not considered ripe (Rehwinkel et al , 1976). 

 Christenson (1975) found sturgeon spawning occurred in the Red Cedar River 

 of Wisconsin at temperatures between 19.4-21.1°C (67-70OF). 



SAMPLING AND TAGGING STUDIES 



Egg and Fry Sampling 



Egg and fry samples were taken at least once each week during the 

 shovelnose sturgeon run in 1975 and 1976 by holding a fine mesh drift sampler 

 in the current for 30 seconds. Three riffle areas were sampled and a drift 

 taken at 10 m intervals across each riffle. Material collected in the net 

 was sorted and washed at the time of collection. Samples were then preserved 

 in 10 percent formalin and hand picked with the aid of a microscope. A few 

 eggs and small fish were taken, but none were positively identified as 

 shovelnose sturgeon. 



Several attempts were made to artifically propagate shovelnose sturgeon. 

 In one attempt, eggs were stripped from a ripe female, fertilized by one 

 male, and incubated in a jar, agitated by air circulating through the eggs. 

 Second, several sturgeon were held at the Miles City National Fish 

 Hatchery until they were considered gravid. Eggs were stripped into a pan 

 and milt added. Half of the eggs remained stationary and the otherhalf were 

 stirred for 30 minutes, allowing the eggs to water harden. Both batches were 

 then placed in hatching jars and kept moving to provide oxygenation. Eggs 

 were cleared with glacial acetic acid to check on development. Because no 

 development was apparent in either attempt, it was assumed that the eggs were 

 not successfully fertilized. 



Tagging Studies 



Weight Losses . In 1975, 28 fish that had been tagged in 1974 with 

 monel tags were recaptured. The monel tag returns demonstrated a significant 

 weight loss of 0.36 kg (0.79 lb) per fish (p f .001). Eight sturgeon 

 (4.5 percent) tagged with anchor tags in 1974 and recaptured in 1975 showed 

 a weight gain of 0.36 kg (0.79 lb) per fish (p = 0.015). In the 1975 samplinc 

 7.9 percent (14 of 178) of the anchor-tagged fish and 12.8 percent (31 of 243) 

 of the monel-tagged fish were returned from 1974. (Only 28 monel-tagged fish 

 were recaptured; three of them were recaptured twice, producing a total of 

 31 recaptures.) Total returns in 1975 were 10.7 percent (45 of 421) of those 

 fish tagged in 1974. 



42 



