What is the life cycle of paddlefish in the Yellowstone-Sakakawea stock?

Mature paddlefish migrate upstream out of Lake Sakakawea into the Yellowstone and Missouri rivers to spawn. Most fish make this migration in early spring, but some start the previous fall. They spawn during high runoff in late spring or early summer. Most fish deposit eggs and milt on flooded gravel bars in the lower Yellowstone River, but some fish migrate up the Missouri River and even into the Milk River in Montana. Soon after spawning, adults typically move back downstream into Lake Sakakawea.

The eggs are fertilized by milt as they are released from the females. When exposed to water, the eggs become very sticky and adhere to gravel and cobble substrate. Incubation time varies depending upon water temperature; eggs hatch in about 7 days in 60°F water. After hatching, young (larval) fish drift downstream, eventually reaching the headwaters of Lake Sakakawea where they spend their first few months. Because of greater zooplankton abundance, older juvenile and adult fish also utilize the upper portions of Lake Sakakawea. With the exception of spawning migrations, paddlefish remain within Lake Sakakawea. Paddlefish typically mature at about age 9 or 10 for males, age 16 to 18 for females. Tagging studies have shown that males spawn more frequently than females. Males spawn every year or every other year, while females typically spawn every second or third year.