Sturgeons are generally solitary, spending a number of years at sea before returning to the river where they were born, in order to breed in their turn. Entering the river in spring, mature individuals migrate upriver to the shallow spawning grounds (4). Females can produce between 200,000 and 6 million eggs, which are sticky so that they can attach to the gravel substrate (4). Mature individuals do not eat throughout the spawning migration (4). As the juveniles grow they begin to migrate downstream, and adult fish spend about seven to eight years at sea before reaching sexual maturity (7). Sturgeon feed opportunistically on bottom dwelling creatures, feeling for prey amongst the mud with the sensitive barbels on their chin. Their food consists mainly of invertebrates and small fish (4).