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The Nature of Summer: Brook Buddies

by Suzanne Petersen, education specialist

Lamprey River Advisory Committee

2010 

In nature, as in society, relationships exist in which everybody wins. One example of this occurs in the Lamprey River. Both brook trout and brook floater mussels are native to the river and rely on clean, cold water to survive and thrive. Brook floater mussels rely on brook trout. Brook trout benefit from having mussels as neighbors.

The NH State Endangered brook floater mussel

Photo by www.ct.gov

Fresh water mussels have a unique adaptation that has co-evolved with certain species of fresh water fish. When mussels reproduce, the males release their sperm into the water and the females filter that water through their bodies. The females collect the sperm and then release the fertilized eggs into the water. The eggs hatch into larvae which attach themselves to specific fish. The larvae travel with the fish for a time, and then drop to the bottom where they will continue to mature into adults. They will spend the rest of their lives, usually 10-15 years but up to 100 years, living in the sediment. The larvae do not seem to harm the fish, so they are not parasites, but the mussels do derive a dispersal benefit from the fish. The fish derives a respiratory benefit from the mussels as they filter the water, cleaning it of debris.

 brook trout, NH State Fish

Photo by www.wildlife.state.nh.us

Brook trout are popular with sportsmen, so NH Fish & Game breeds and stocks them. Some “brookies” probably still breed in the river, but most are stocked at present. Brook trout are susceptible to pressures from fishermen, but they are also vulnerable to pressures caused by impaired water quality. Additional and likely more significant pressure comes from nutrient pollution, siltation, and increased temperatures caused by removal of shade trees along the river or warm run-off from paved surfaces. The same impairments that affect trout also encumber fresh water mussels. They are easily recognized by the white band on the leading edge of the fins. This species spawns in fall and eggs hatch 2-3 months later as “fry”. Most will spend their entire lives in the stream in which they hatch, but some head to sea, returning to their natal stream to spawn.