2021 marks the 150th anniversary of the United States Fish and Wildlife Service. Since its origins in fisheries conservation in 1871, there have been tremendous changes in the upper Mississippi. But for freshwater mussels, the need remains the same; populations of species and their communities resilient to change and local impacts. This is not to say that historic harvest, hydrological changes, pollution and introductions of invasive species in the intervening period have not caused declines, extirpations (when a species is eliminated from an area, but is not going to disappear), and the need for protection and management at the state and federal levels, but that our objectives are the same. What does environmentally resilient mean? Perhaps it is better to think of species as ships. Some are able to withstand a hurricane at sea or crossing the Drake Passage to Antarctica when even the unsinkable Titanic failed to cross the North Atlantic. The most resilient species are numerous enough to withstand reproductive failures, loss of parts of their populations, genetic diversity for future adaptation to their environment, so we need to find ways to recognize and protect that very resilience. among our common species to maintain the resilience of their communities, ecosystems and the biosphere.
What does resilience mean for freshwater mussel populations and communities? This is a complex question and we do not have specific parameters for most species, let alone for most communities. This year at the hatchery, we conducted two surveys as additional steps to identify characteristics of resilient populations. One on the Chippewa River where two federally threatened mussel species, the Winged Maple Leaf and the Higgins Eye Pearl Mussel were reintroduced and one in Guttenberg, IA on the Mississippi River where a train derailment took place. was produced in 2008. The data from each survey represents a different part of the Resilience Web.
For the reintroduction on the Chippewa, a formula was used to calculate the persistence of a number of mussels to be released based on an estimate of the chances of survival, area and percentage of the community we wanted. they represent, according to other communities of freshwater mussels. where they are. Our survey shows that our estimate of five-year survival was very conservative, and that there are likely many more Higgins Eye persisting in the population than we expected. These data are helping us refine what the mortality and survival of this species might look like since all of the Higgins Eye pearl mussels found in the area have been placed there. Guttenberg’s survey examines the reaction of what was probably a former stable community of freshwater mussels to an acute event, or the proverbial cannonball from above. This year’s survey shows that mussel densities returned to current levels just after the event thanks to the support of the hatchery reintroduction efforts and that the subadult mussels added to the site have survived and thrived.
These efforts, while small within the larger framework of freshwater mussel conservation, could play a role in understanding what it means for a mussel species or community to be resilient in the future. by promoting the recovery of individual species in the Chippewa and Mississippi rivers. Each mussel collected in a cage, tagged or placed in rivers by our volunteers and biologists subtly shapes the science of freshwater mussel recovery and this is a pretty big change from some pretty tiny mussels.
By: Megan Bradley