Description of the reproductive structure, size, growth, and condition of hatchery-origin white sturgeon in the lower Columbia River, British Columbia, Canada

Abstract

Conservation aquaculture has been successful in preventing extirpation of endangered white sturgeon Acipenser transmontanus in the lower Columbia River (LCR), Canada. The goals of this project were to 1) determine if the hatchery-origin (HO) population has reached puberty as many fish are of an age and body size to begin contributing to spawning and 2) assess the size, absolute growth rate (AGR), and relative condition factor (Kn) of the population. The reproductive structure (sex and stage of maturity) of the HO population was assessed using multiple tools (gonadal biopsy analyzed histologically, ultrasound, endoscopy, and plasma sex steroids). The accuracy of each tool was determined by comparing the assigned sex to the true sex determined by histological analysis of a gonadal biopsy. A subobjective was to determine whether gonadal development was homogenous (assessed in fish captured in LCR and Lake Roosevelt, WA, USA). All fish assessed were pre-meiotic males (n=158) or pre-vitellogenic females (n=174) and had yet to reach puberty. Endoscopy and gonadal biopsy analyzed histologically were the most accurate tools with accuracies > 97%. Gonadal development was homogenous in females but 38% of the males exhibited non-homogenous testicular development, with a few precocious cysts that contained germ cells in an advanced stage of development compared to the predominant phase seen throughout the biopsy. The size, AGR, and Kn were compared among sex, age, and river zone. While the mean Kn indicated that the HO white sturgeon were in average condition relative to all HO fish within the LCR, they were lower in condition compared to the full transboundary population (Canada and USA). This reflects a difference in the environmental or physiological conditions of the fish in the LCR and those captured throughout the transboundary reach. Results of this work will be important to determine the reproductive dynamics of the hatchery-origin population over time (e.g., age and size at puberty, sex ratio), and specifically when these fish will begin spawning in the wild. Additionally, this information will help to develop other standardized monitoring programs which can track the reproductive structure of a population over time using tools with known accuracy rates.