632 



Fishery Bulletin 94(4), 1996 



98,200 to 699,000 eggs for fish 115 to 215 cm FL 

 (DeVore et al. 1 ). Comparisons of egg diameters in ripe 

 females from the Sacramento and Columbia rivers 

 revealed that female sturgeon from the Sacramento 

 River had larger eggs (3.4-^1.0 mm) than those found 

 in females from the Columbia River (2.6-3.6 mm) 

 (North et al. 2 ). This difference may account for the 

 apparent higher fecundity of white sturgeon females 

 in the Columbia River. We found no relation between 

 size of the female sturgeon and mature egg diam- 

 eters. Lutes et al. (1987) also did not detect a rela- 

 tion between female body size and diameters of 

 postvitellogenic oocytes in white sturgeon. 



The size at which white sturgeon attain sexual 

 maturity appears to vary between populations. Our 

 observations indicate that female white sturgeon in 

 San Francisco Bay mature at larger sizes (>95 cm) 

 than males (>75 cm). Because the proportions of rip- 

 ening individuals (groups 2 and 3) increased and sta- 

 bilized above 135 cm in females and 105 cm in males, 

 recruitment into puberty most likely occurs from 95 

 to 135 cm for females and from 75 to 105 cm for males. 

 In the Columbia River, female white sturgeon did 

 not mature until they were even larger ( 160-193 cm 

 FL), revealing significant size variations in the river 

 downstream from all dams and between different 

 river reservoirs (DeVore et al. 1 ; Welch and Beames- 

 derfer 3 ; Beamesderfer and Rien 5 ). These differences 

 in size at first sexual maturity were largely attrib- 

 uted to food availability and hydrologic conditions. 

 Working with wild and domestic stocks, Chapman 

 (1989) postulated that size and age at sexual matu- 

 rity in white sturgeon were dependant on body size 

 and nutrient composition. Size or age at sexual ma- 

 turity, however, could be modified by growth, nutri- 

 tion, and environmental factors. 



Examination of the stage of gonadal development 

 in different length classes of white sturgeon females 

 in San Francisco Bay indicated a high fraction of 

 group- 1 (immature) individuals. The proportions of 

 group-2 (maturing) and group-3 (ripe) females in the 

 sampled population were low ( 12% and 18%, respec- 

 tively); ripe females represented only 9% of all stur- 

 geon sampled. Similar observations in the Columbia 

 River system revealed even lower proportions, 6% 

 maturing and 2% ripe (DeVore et al. 1 ; North et al. 2 ; 

 Welch and Beamesderfer 3 ). From histological analy- 

 sis of oogenesis (Chapman, 1989) and from the pro- 

 portions of different ovarian stages in the white stur- 

 geon population of San Francisco Bay, we assume 

 that iteroparous sturgeon females require longer 

 than one year to complete an egg development cycle, 

 including vitellogenic growth and prematurational 

 polarization of the oocyte. Because the proportion of 

 females with ripe ovaries (group 3, >135 cm) was on 



average 25% of all sampled individuals, the interval 

 between two consecutive spawnings is most likely 

 between 2 and 4 years. Our recent observations of 

 domestically raised and continuously fed white stur- 

 geon suggest predominantly biennial ovarian cycles. 

 Because wild female sturgeon, compared with other 

 fish including domestic sturgeon, lose a substantial 

 percentage of weight and energy at spawning 

 (Krivobok and Tarkovskaya, 1970), it is possible that 

 they defer a new wave of ovarian vitellogenesis for 

 some time after spawning, allowing recovery from 

 spawning depletions (the high percentage [59%] of 

 fish in group 1 strongly suggests this event). A final 

 conclusion regarding spawning periodicity of white 

 sturgeon cannot, however, be reached until fish that 

 have been tagged are recaptured and sampled re- 

 peatedly or until the size and age interval of female 

 recruitment to puberty is known. These are impor- 

 tant considerations, because pubertal age of white 

 sturgeon females may extend from 15 to 32 years 

 (White Sturgeon Planning Committee 6 ). 



Considering the season of our sampling (late fall- 

 early winter) and the potential overlap between mei- 

 otic and maturational phases of testicular develop- 

 ment, the adult male white sturgeon may spawn 

 annually ( as in commercial hatcheries ) or biennially. 

 Existence of a biennial cycle in sturgeon males could 

 be verified by continued sampling throughout spring 

 and summer. Most spawning males accommodate the 

 protracted spawning season (February-June) of fe- 

 males. This shorter reproductive cycle, which is asso- 

 ciated with annual spawning migrations, may also re- 

 sult in a higher mortality for older and larger males. 



A 2-4.5 year spawning period has been suggested 

 for female white sturgeon in the Columbia River 

 (Welch and Beamesderfer 3 ). According to Trusov 

 (1975), the refractory ovarian stages in iteroparous 

 sevryuga, A. stellatus, last 2 to 5 years, whereas the 

 ovarian vitellogenesis occurs within 1 to 2 years. 

 Examining the sexual maturation of Russian stur- 

 geon, A. guldenstadti, in the Sea of Azov, Kornienko 

 et al. (1988) found that 72% of the sampled adult- 

 size fish had either immature or refractory ovaries 

 and that the remaining fish were approximately 

 equally distributed between "maturing" and "ripe." 

 In males, spermatogenesis was a continuous process. 



We conclude that sexual maturation in white stur- 

 geon is prolonged. Females mature slowly, and first 

 maturation takes place over a wide range of body 

 sizes. The average interval between spawnings by 

 iteroparous females appears to range from 2 to 4 



H White Sturgeon Planning Committee. 1992. White sturgeon 

 management framework plan. 2501 S.W. First Avenue, Pacific 

 States Marine Fisheries Commission, Gladstone, Oregon. 



