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| 8/2/2006 4:00:00 AM | Email this article • Print this article
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Photo by Kirsten Brennan
Willapa National Wildlife Refuge staff recently witnessed a fascinating natural event, the spawning of western brook lampreys. Living in fresh water in a larval state, individuals die within months of transformation into the eyed form pictured above. |
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Western brook lamprey makes annual appearance at refuge
By Marie Fernandez
Wildlife Biologist
In early May, several of the refuge staff and volunteer Russ Lewis were able to witness a truly impressive natural event - the mass spawning of the western brook lamprey.
The western brook lamprey (Lampetra richardsoni) is a member of the Family Petromyzontidae. Petromyzon is Greek for "stone sucker" and this is an apt description for this jawless fish. Many people refer to lampreys as "eels." Although both share a similar body shape, eels are jawed fish and have a true backbone.
Lampreys are considered one of the most primitive fish as they have no jaws, true backbone or ribs. Their skeleton is soft and cartilaginous and they are scaleless. The lamprey is a specialized survivor of the first vertebrates, the mud-grubbing jawless fishes that made their appearance in the world's oceans some 450 million years ago.
Three species of lamprey are found in Washington - the western brook lamprey, Pacific lamprey and the river lamprey.
The western brook lamprey is a tiny fellow, compared to its relatives. The adults of this species vary in length from 5- to 7-inches. Females are smaller than males. Unlike the Pacific lamprey (maximum length is 30 inches) and the river lamprey (average length is 12 inches), the western brook lamprey is not a parasite and does not exhibit an ocean-going (pelagic) phase in its life history. In fact, it spends its entire life in fresh water.
The circular oral disc of the western brook lamprey is small and the teeth are non-functional as the adults never eat. The only function of adults is to reproduce. The other lamprey species found in Washington have fully developed teeth as adults and primarily feed on several species of fish during the period that they reside in the ocean. Scars from the Pacific lamprey have even been found on several species of whales!
The spawning period for the western brook lamprey is generally the months of April, May and June. When a suitable site for spawning is reached, the male and the female begin to build a nest in which the eggs are deposited. The ideal nesting site of the lamprey is in shallow water with a bottom of coarse gravel and pebbles, with a moderate current. Nest building consists of the male and female grasping pebbles and gravel with their mouths and moving them, making a small depression about 4- or 5-inches in diameter, generally at the head of a riffle. The eggs are released in the gravel by the female and fertilized by the male.
Sometimes a large number of western brook lamprey spawn together in a tight cluster - the refuge staff has counted as many as 12 squirming together over one depression.
As many as 3,700 tiny oval eggs may be produced by one female. The eggs are adhesive which helps prevent them from being washed downstream. They spawn only once and adults die soon after the eggs are deposited.
In about 10 days, depending on the water temperature, eggs hatch into eyeless larval forms called ammocoetes. They drift downstream until they reach mud or silt in backwater areas or quiet eddies where they burrow into the sediment. The ammocoetes are filter feeders. They take in mud and water through a hood-like extension of their oral discs and filter it, consuming a variety of microorganisms and detritus. As many as 170 ammocoetes per square meter have been documented in some coastal streams.
Western brook lamprey may live six years. The larval stage can last more than five years after which they transform into eyed adults. The adult western brook lamprey live only a few months.
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