Population viability of the Gulf of Mexico sturgeon: Inferences from capture-recapture and age-structured models

The Suwannee River, Florida, population of the Gulf of Mexico sturgeon Acipenser oxyrinchus desotoi, a subspecies of Atlantic sturgeon A. oxyrinchus oxyrinchus, was evaluated using a capture-recapture approach and an age-structured model to examine population trends from 1986 through 1995. The capture-recapture analysis revealed a positive rate of change (λ) in the adult population, indicating that it was slowly increasing from the mid-1980s through the mid-1990s. The age-structured model revealed that the population was highly sensitive to changes in egg-to-age-1 mortality, the percentage of females that spawn annually, and adult mortality. The model predicted that even slight increases in annual adult mortality (from 16% to 20%) would result in a decline in the Suwannee River Gulf sturgeon population. Population trends were consistent for both modeling procedures and were similar to those in published reports. Although this population is currently expanding, care should be taken to protect adult fish from any fishing or bycatch mortality. Given the particular attributes of Gulf sturgeon (such as late sexual maturation, the fact that few mature females spawn each year, and high early life mortality), managers should be patient and willing to monitor populations for extended periods of time (∼20 years) to detect changes in the adult population.