The Outside Story: Sea Lamprey, scary looking, but good for the river

By David Deen

Most people do not like sea lampreys even though they have never even seen one. The fish have a bad reputation as an invasive species in Lake Champlain. Their appearance is also alarming. These are the fish you occasionally see on the television news, with long, snake-like bodies and suction cup mouths full of teeth. They use those toothy mouths and rasp-like tongues to latch onto other fish, cut into their skin, and drink their body fluids.

Yet the same fish that is a scourge in the lake is also present in the Connecticut River, where it causes no trouble, and therein lies a story.

The difference has to do with the unintended consequences of human intervention and differences in life cycles. Although there is disagreement about where and how long sea lampreys have lived in the Great Lakes, what is clear is that manmade canals have allowed the lamprey to spread and thrive, to the detriment of other lake fish. Whatever their origin, Lake Champlain lamprey, although still called sea lamprey, never swim in the ocean. They have adapted to live their entire lives in fresh water, including their adult, parasitic stage when they prey on other fish.

The sea lampreys in the Connecticut River, however, are anadromous, meaning that they are born in fresh water but spend their adult lives in the ocean. They only return to inland waters when they are preparing to spawn. As with all other truly anadromous fish, their return from the sea coincides with dramatic internal physiological changes that end all feeding activity. During their journey upriver to spawning sites, they live on fat reserves and do not attack other fish.

To select a spawning site, sea lampreys seek out the scent of previously spawned larvae buried in the mud. Their eggs hatch into small larvae known as ammocoetes. These larvae burrow into the mud, filtering out algae, small organisms and waste as food. They remain in fresh water for up to ten years, drifting farther downstream each year.

Looks and reputation aside, there is a lot to appreciate about this native fish. Sea lampreys are ancient. Fossil evidence shows they have traveled our oceans and rivers for 360 million years. Although they are sometimes confused with eels, they are not closely related. They differ from eels and most fish, in that they lack bones, jaws, and paired fins. Just like the equally ancient shark, lamprey skeletons are made of cartilage. They have well-developed eyes, a single nostril on top of the head and seven gill openings on each side of the body. They can grow up to 40 inches long.

Sea lamprey are weak swimmers but in some circumstances they use their mouths to help get around obstacles. Their taxonomic name is Petromyzon marinus. Petromyzon roughly translates from the Latin into “one who suckles stone,” and in fact, they sometimes navigate waterfalls by attaching themselves by mouth suction to flat areas on a stone. They dead-hang in place until they feel the flow of the water pulse and lessen; when it does, in that small window of time, they wiggle upward and attach again at a higher point on the rock face.

Once they reach their spawning site, sea lampreys build concave circular nests by thrashing their bodies to clean sediment off the bottom, and if necessary, by removing one stone at a time using mouth suction and swimming it out of the nest. Male and female intertwine over the nest to deposit and fertilize eggs. The nest-building is a hard-wired, instinctive activity; if you throw stones back into the nest as they are clearing it they will just keep removing the stones until the nest meets their requirements.

There are benefits to having this fish in the Connecticut and its tributaries. Sea lampreys transport trace elements from the ocean, improving the chemical balance of the river. Fish and marine mammals like to eat them because of their high fat content and because they are easier to catch than most other fish. Their silt-free concave nests are attractive spawning sites for other fish that make nests, such as salmon.

Sea lampreys may not be pretty or prestigious, but their function is important in the Connecticut River watershed. If you want to see them, head to any tributary stream in early June and look in moving shallow water for their thrashing bodies.

David Deen is River Steward for the Connecticut River Watershed Council. CRWC has been a protector of the Connecticut River for more than half a century. The illustration for this column was drawn by Adelaide Tyrol. The Outside Story is assigned and edited by Northern Woodlands magazine and sponsored by the Wellborn Ecology Fund of New Hampshire Charitable Foundation: wellborn@nhcf.org