Potential Classification of Sex and Stage of Gonadal Maturity of Wild White Sturgeon Using Blood Plasma Indicators

—Because white sturgeon Acipenser transmontanus show no readily discernible external signs of gender, management agencies use surgical biopsies to determine the sex and stage of gonadal maturity of individuals. This procedure is highly invasive and can be difficult under field conditions. Therefore, gonadal tissue and blood were collected from white sturgeon captured in tribal and commercial fisheries (fishery fish) and by fish and wildlife agencies (oversize fish) in the Columbia River basin to develop a method of determining sex and stage of maturity using the blood plasma indicators testosterone (T), 11-ketotestosterone (KT), estradiol (E2), and calcium (Ca21). The sex and stage of maturity was determined by histology or by visual examination in maturing fish. Plasma sex steroid levels were measured by radioimmunoassay, and plasma Ca21 was measured spectrophotometrically. White sturgeon showed sexand maturity-specific levels of steroids and Ca21. Stepwise discriminant function analysis (DFA) was used to choose the best variable(s) for predicting sex and stage of maturity, and quadratic DFA was conducted to classify fish into two groups of sex or four groups of sex and stage of maturity. In the classification of the fishery plus oversize fish, plasma T and E2 were the best predictors of sex and stage of maturity. Of the 151 females and 106 males, 85% of the females and 79% of the males were correctly classified; 88, 72, 98, and 96% of the immature females, immature males, maturing females, and maturing males, respectively, were correctly classified. The greatest error of misclassification occurred with immature males classified as immature females. In the analysis of immature fishery fish only, plasma T and fork length led to the correct classification of 88% of the females and 86% of the males. In the analysis of oversize fish only, 100% of the females and 95% of the males were correctly classified using plasma T and E2; 93, 100, 98, and 100% of the immature females, immature males, maturing females, and maturing males, respectively, were correctly classified using these variables. The derived classification functions for the prediction of sex or sex and maturity may replace the need for surgical biopsies if the error associated with the misclassification of immature fish is acceptable. The life history characteristics of long life and late maturity have sustained sturgeon, Acipenseriformes, populations since the end of the Jurassic (Grande and Bemis 1991); these same traits, however, are detrimental to populations faced with * Corresponding author: [email protected] Received September 8, 2000; accepted August 1, 2001 habitat alterations and overexploitation (Rieman and Beamesderfer 1990; Beamesderfer and Farr 1997). Most sturgeon populations worldwide are threatened or endangered, and efforts for protection and restoration are critical for their survival (Birstein 1993). Reproduction provides a key to the future success of sturgeon populations, and understanding reproduction becomes ever more crucial for successful management. 133 STURGEON SEX AND MATURITY Sturgeon are economically and culturally important in the Pacific Northwest and are harvested by recreational, tribal, and commercial fisheries throughout the Columbia River basin. Hydroelectric development of the Columbia River from 1938 to 1967 led to functionally discrete populations of white sturgeon Acipenser transmontanus (North et al. 1993) and reduced productivity in impounded sections of the river (Beamesderfer et al. 1995). The Lower Columbia River has four dams from the Snake River confluence to the mouth of the Columbia River. The Snake River has four dams from the Columbia River confluence to the Washington–Idaho border. Population characteristics of sturgeon between reservoirs and among reservoir and unimpounded populations (below Bonneville Dam extending to the ocean) differ significantly; therefore, the sturgeon fisheries are managed with stock-specific regulations (Beamesderfer et al. 1995; Beamesderfer and Farr 1997). The current sturgeon population in the unimpounded Columbia River is similar in size to that existing before overexploitation in the late 1880s (Beamesderfer and Farr 1997) and supports one of the most productive sturgeon fisheries in North America—and potentially, the world (DeVore et al. 1995). However, the continued productivity of sturgeon in both the unimpounded and impounded sections of the Columbia and Snake rivers is dependent on successful fisheries management. Successful management of sturgeon populations requires knowledge of the stock composition with regard to sex and maturational status. Harvest rate guidelines are based on sustainable rates derived from sturgeon population models that are extremely sensitive to sex ratio, age at first maturity, and spawning frequency. Sturgeon are not obviously sexually dimorphic; therefore, sex and stage of maturity are currently determined through gonadal biopsy. This technique is invasive, and the collection of gonadal tissue from immature fish is often difficult, requiring histological confirmation. It would be beneficial for fisheries management to have a less invasive test for discriminating between the sexes and stages of maturity. In sturgeon, plasma sex steroid concentrations are low or undetectable until gonadal differentiation. With the onset of meiosis, plasma concentrations of testosterone (T) and 11-ketotestosterone (KT) increase in both males and females (Cuisset et al. 1995; Moberg et al. 1995) and remain elevated throughout ovarian (Cuisset et al. 1995; Amiri et al. 1996b; Van Eenennaam et al. 1996; Webb et al. 1999; this study) and testicular (Cuisset et al. 1995; Amiri et al. 1996a; Van Eenennaam et al. 1996; this study) development. Plasma estradiol (E2) and calcium (Ca21) increase during the vitellogenic phase of ovarian development in sturgeon and decrease during the final stages of oocyte maturation (Linares-Casenave et al. 1994; Amiri et al. 1996b; Doroshov et al. 1997; Webb et al. 1999). Total plasma Ca21 in cultured white sturgeon females has a significant linear relationship with plasma vitellogenin (R250.96, N 5 72) and was therefore used as an index of vitellogenin. Because plasma sex steroids and Ca21 in sturgeon are sex-specific and maturity-specific, they may be used to differentiate males and females at various levels of development. Therefore, our objective was to develop a method to determine the sex and stage of maturity of wild white sturgeon using blood plasma indicators, sex steroids, and Ca21.