By Staff
When I was a wee nipper our family doctor used to take me on occasional visits to his parent's place up in Harbor Springs. Doc's father was my quasi-grandpa and nearly every morning “gramps” and I went perch fishing from the big wooden dock extending out into Lake Michigan. Back then the water was crystal clear and we could see schools of jumbo perch hanging around the pilings far below the water surface. Once in a great while a lake trout would come cruising by and every one had lampreys hanging from its sides like a cluster of ribbons. This was in the late 1950s and early 1960s when Great Lakes lake trout were teetering on the brink of extinction from sea lamprey predation.
Sea lampreys are native to the coastal shorelines of the Atlantic Ocean. They are anadromous, meaning the adults live in the ocean but spawn in freshwater. Lampreys first invaded Lake Ontario in the 1830s via newly constructed shipping canals and locks but they were blocked from the rest of the Lakes by Niagara Falls. Then in 1919 the Wellington Canal, which bypassed Niagara Falls ,was improved, opening the door to the rest of the lakes. Within 20 years sea lampreys were flourishing throughout the entire Great Lakes system.
Starting about 1940 lake trout began to seriously decline, mostly from over fishing. This was also when lamprey numbers were growing rampantly and they joined in to ravage what lake trout were left. By 1960 the trout were all but gone. Adult lampreys feed by attaching to relatively large fish with their sucker mouths. Numerous teeth around the rim of the mouth clamp into the fish to ensure the lamprey can't be shaken off. Teeth on the lamprey's tongue rasp a hole into the fishes flesh and the lamprey sucks blood from this wound. An anticoagulant in the lamprey's saliva keeps the blood flowing. In the ocean the lamprey's natural prey are large and rarely succumb. However, lake trout are smaller and roughly half of those attacked by lamprey bleed to death.
The loss of lake trout had far reaching affects. Sport fishing for them, of course, was over and many commercial fishermen were out of work. The entire ecosystem fell out of balance. Without trout predation, alien prey species like smelt and alewives flourished, crowding to extinction small native species such as certain sculpin and deep water cisco. Because of the immense number of alewives there were annual die-offs that covered the beaches with dead alewives. The carcasses and ensuing stench impacted beach related tourism. Alewives and smelt feed on zooplankton so these tiny creatures drastically declined. Zooplankton feed on microscopic plants called phytoplankton. Phytoplankton flourished, affecting the clarity and color of the Great Lakes water.
In 1959 the U.S. and Canada joined forces to control lampreys. Lampreys are not eels as many think, but primitive fish. Only adult lampreys feed on fish and the adults only live one year. In the spring they enter streams, spawn and die. The eggs soon hatch into larvae which burrow into the stream bottom where they remain anywhere from three to 10 or more years. The larvae eventually emerge as juvenile lampreys which leave the stream, grow into adults and spend the next year vampiring fish. Then the cycle repeats. The original control method was weirs that blocked adult lampreys from entering streams. However, weirs are costly and require constant tending. Later, a chemical was found that kills lamprey larvae but does little or no harm to other fishes. It is cheaper and less labor intensive than weirs and is the primary control method in use today. Improved stream blocking systems also play a role. With these control efforts lamprey numbers in the Great Lakes have held steady at around 10 percent of former levels.
The latest buzz is scientists have recently identified and duplicated a pheromone that attracts lampreys. They also have a chemical that sterilizes the males. The idea is to draw spawning lampreys to controlled areas and sterilize the males to effectively cut off breeding with minimal expense and labor. Early tests indicate this has great promise. Could this along with ship ballast water control mean bye, bye lamprey? Only time will tell. Carpe diem.