We're used to thinking of sea lampreys as a bad thing, an invasive species. But that's in the Great Lakes. In New England streams, the lampreys are native and necessary to ecosystem health.
This video features healthy sea lampreys spawning in a Massachusetts stream. The cool part that you should be watching for: Lampreys picking up stones with their sucker mouths and moving the rocks from one spot in the stream to another. Essentially, they're digging — moving and discarding stones to leave behind 6-inch-deep furrows in the rocky stream bed, which is where the lampreys lay their eggs. They've been known to move stones as big as a human fist.
What's more, this behavior isn't just good for the lampreys and their sex lives. It also improves the health of stream ecosystems.
Sea lamprey spawning activities restore and enhance streambed structure that benefits many other species. Some minnow species use sea lamprey nests for their own spawning activities and salmonids find the loosened and cleaned substrate desirable as redd building sites and as refugia for some life stages of their offspring. Improved water flows through loosened substrate are also beneficial for biologically important aquatic insects and other invertebrates.
Great work, lampreys!