Freshwater
Mussels of the Upper Mississippi River System
Figure 6. Age frequency of washboard mussels sampled by biologists in 1995-1998.
Washboards have the potential to reproduce beginning at 7 years of age; however, only a small percentage are mature enough to do so. As they become older, a higher percentage of the individuals of that age are sexually mature. Studies have documented that it is not uncommon for some species of mussels to successfully reproduce only once out of seven or more years. Therefore, when interpreting the graph, one must realize that the sub-legal adults may only have one, or at most two, successful reproductive cycles before they are large enough to be harvested.
