Freshwater mussels once dominated the benthic biomass of southern rivers but are now among the most endangered animal groups on Earth, with most North American species considered imperiled due to habitat loss and alteration, and anthropogenic stressors that degrade and fragment lotic habitats. Numerousstudies have documented decreases in diversity and abundance among freshwater mussel assemblages in southern U.S. rivers due to several anthropogenic factors. Freshwater mussels have a complex life history that includes an obligate parasitic larval stage that must attach to fish to develop. Because freshwater mussels rely on a host fish for larval development and longdistance dispersal, degradation of fish habitat and loss of habitat connectivity can adversely affect freshwater mussel populations. Therefore, there is a critical need to better understand freshwater mussel distribution and abundance in contemporary fragmented habitats.

Louisiana’s freshwater mussels are no exception. In the past, in addition to the impacts of habitat loss and alteration, Louisiana’s freshwater mussels experienced extensive harvest for the textile industry. Thus, it is no surprise that Louisiana is home to species of conservation concern, including the federally threatened species, the Louisiana pearlshell (Margaritifera hembli) and the Louisiana pigtoe (Pleurobema riddellii), the latter of which is being assessed for potential federal listing.

Given their life history, road crossings intersecting waterways can be particularly challenging for freshwater mussels and their fish hosts to disperse through. Poorly designed culverts, bridges and other structures often fragment stream habitats and contribute to freshwater fish and mussel population declines and high rates of imperilment. Road-stream crossings block passage by all or some freshwater animals at up to 97% of locations within some watersheds. However, locating impassable road-stream crossings can be challenging because not all crossings are constructed similarly, even within a single watershed. There is a need to account for crossing barriers across broad spatial scales to assist with connectivity conservation planning. Once the distribution of road-stream crossings that block organism movements is known, biologists can identify and prioritize the crossings most in need of remediation.

Drs. Garrett Hopper, Mike Kaller and Bill Kelso were awarded a State Wildlife Grant to assess habitat connectivity in the Bayou Pierre watershed, update historical occurrence records and obtain data on status, distribution and abundance of mussels listed by Louisiana as species of concern. To meet these objectives, they will conduct mussel and habitat surveys and assess 300 road-stream crossings identified in the National Aquatic Barrier Inventory and Prioritization Tool in the Bayou Pierre watershed. This project will support the graduate research of Julia Morin and provide field experience for several undergraduates.

Freshwater mussels collected during a survey in the Bogue Chitto River in 2024.