Monster or Valuable Asset to Our River Systems?

Monster or Valuable Asset to Our River Systems?

Many people see these creatures as a nuisance. Many also think that they are invasive. While they look like a prehistoric monster type eel, they are far from the monster many think they are. We in the Northeast do not live in the Great Lakes, in which the sea lamprey is invasive and very distructive, and those sea lampreys in Lake Champlain, well, we are not 100% sure whether they came through the Hudson River and Champlain Canal or whether they are native to the lake as recent studies have indicated.

Sea lampreys are a parasitic fish native to the Atlantic Ocean. They have remained largely unchanged for more than 340 million years and have survived through at least four major extinction events. Sea lampreys are unique from many other fishes in that they do not have jaws or other bony structures, and instead possess a skeleton made of cartilage. While sea lampreys resemble eels, they are not related and are set apart by their unique mouth: a large oral sucking disk filled with sharp, horn-shaped teeth surrounding a razorsharp rasping tongue.

Sea lamprey pulled off a striped bass by Michael Linnen on 4/27/2017, caught in the Housatonic River.

The sea lamprey is an anadromous (sea-run) fish native to coastal North Atlantic watersheds. Adult sea lamprey spend 1-1/2 to 2 years in the ocean, where they grow to maturity, after which they return to rivers and streams for spawning. Incubation takes 10 to 13 days and once the eggs hatch, larval sea lamprey stay in the nest for 4 or 5 more days during which time they develop gills, pigmentation and buccal hood. They then drift downstream where they burrow into the muddy bottoms of streams, rivers and lakes. These ammocoetes stay in the substrate for 4 to 8 years filter feeding upon planktonic drift. Eventually, they emerge from their burrows and metamorphose into transformers, the migration life stage which is similar to the final adult form.

Anadromous sea lamprey benefit freshwater habitat in several ways:

  1. Sea lamprey bring valuable nutrients into freshwater systems and provide a valuable source of food for a variety of birds, fish, and mammals, including people. Fisheries biologists have observed aquatic species foraging on lamprey eggs, striped bass and other species eating emigrating transformers, and caddisfly larvae consuming lamprey carcasses.
  2. Out-migrating sea lamprey transformers export valuable nutrients back to the sea.
  3. 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.
  4. The sea lamprey is also an irreplaceable study specimen for medical research because of its several unique biological functions.

Key points:

  1. Although adult sea lamprey prey on other fish in the ocean they do not attach to other fish or feed in freshwater and die soon after spawning.
  2. Larval sea lamprey spend 4 to 8 years burrowed in stream, river, and lake substrate where they feed entirely on planktonic drift.
  3. Newly transformed lamprey typically spend only a few months in fresh water before heading to sea. They may briefly attach to, and possibly feed upon other freshwater fish species, in a manner that is almost always non-lethal.
  4. Transformers are more likely to attach to, or feed on, other fish in freshwater if downstream passage is delayed by low flows or impediments to passage such as dams. To minimize the potential for attachment or feeding by transformers, river managers should ensure effective downstream passage so that transformers are most likely to migrate downstream without over-wintering delays.

The information in this was compiled from a couple of sources:


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