Faculty Research & Creative Activity

Publication Date

January 1998

Abstract

Due to the collapse of the historic caviar fisheries in the Volga River and Caspian Sea, the demand on domestically produced caviar has increased. To supply the increased demand, the harvest of the shovelnose sturgeon Scaphirhynchus latorynchus has increased. Because caviar fisheries preferentially harvest females, information regardingthe sexual demographics of these populations is essential for effective fisheries management. To date, knowledge regarding the sex ratios and reproductive development of the shovelnose sturgeon population in the Middle Mississippi River is lacking. In Chapter 1, I describe this problem in detail and in subsequent chapters I explain how I addressed this problem using a combination of field and laboratory techniques.

The shovelnose sturgeon and other acipenserids have no known sexually dimorphic traits, making field identification of sex difficult. Thus, in Chapter 2, I developed a non-surgical method for the determination of sex of shovelnose sturgeon. Ultrasound imaging was used to determine the sex of shovelnose sturgeon (n=51). Overall, ultrasound imaging provided an effective method for determining sex, with 86% correct identification of all individuals examined. Ultrasound was ineffective at determining the sex of post spawn females, with 60% being incorrectly identified as males. This method would allow managers to quickly identify sex in the field so that the sex ratio of the shovelnose sturgeon populations could be tracked and population dynamics can be modeled.

Understanding of the sequence of gonadal development allows for the determination of spawning stock size in a given year. This information is currently lacking for the shovelnose sturgeon. To address this, I developed a guide for shovelnose sturgeon reproductive development in Chapter 3. Shovelnose sturgeon were sampled seasonally from the Middle Mississippi River to account for all stages of reproductivedevelopment. I found that stages of gonadal development of the shovelnose sturgeon were both grossly and histologically similar to those of other sturgeon species. This sample allowed me to estimate the sex ratio in the population using an unbiased approach. The shovelnose sturgeon population in the MMR did not differ from 1: 1.

The shovelnose sturgeon has been extirpated from several portions of its historic range. Conservation aquaculture can be used to reestablish shovelnose sturgeon populations to these regions. This requires detailed information about early life history which is currently unavailable. In Chapter 4, I described the stages of development of embryonic and larval shovelnose sturgeon to resolve this issue, giving culturists the ability to track the development of their spawn using proper development as an indicator of success. Additionally, otoliths provide little use in determining hatch date in the acipenserids. Using this information, managers will be able to determine hatch date using stage of development and river temperature.

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