The Grasse River, a tributary to the St. Lawrence River in northern New York, underwent a U.S. Environmental Protection Agency Superfund-led cleanup effort to remove or otherwise isolate polychlorinated biphenyls (PCBs) from the environment. Prior to the remedial activities, which include dredging of nearshore areas and capping of sediments in the main channel, the New York State Department of Environmental Conservation (NYSDEC) in cooperation with the New York State Museum and the Saint Regis Mohawk Tribe, relocated a portion of the freshwater mussel stocks in the river out of the areas expected to be disturbed by the remediation. Surveys showed that the Grasse River had a dense and robust mussel community, with 11 different mussel species identified in the lower river prior to the restoration efforts, four of which are listed as Species of Greatest Conservation Need (SGCN) in New York. Because the remedial project extended along a 7.2 mile stretch of the river, NYSDEC estimated that up to 1.4 million mussels could be impacted during the dredging and capping.
This unique and innovative mussel recovery effort was a planned 5-year effort. The initial phase, in 2017 and 2018, focused on collecting mussels from shallow water areas affected by the remedy and holding a portion of them in cages to be relocated to affected areas after the remediation is complete. In 2019, the project added greater collection of mussels from shallow water areas and relocating them to nearby parts of the river that were not targeted for dredging to assist in recovery of populations after the project is over.
Fathom Resources was contracted to conduct the mussel collection and relocation activities in 2019 and perform all in-water collection work, including all required vessel support and biologist support to assist in specie identification. The basic work plan assumed three dive crews, each consisting of a pair of divers and a support crew of 2, collecting mussels for 12 weeks of the construction season. The work started as soon as the water temperature was safe for divers, typically occurring sometime in early June. A typical survey day consisted of:
- travel to boat launch area and then upstream to targeted river transect location,
- gear-up and start in-water search for all freshwater mussels at the direction of NYDEC and client staff on site,
substrate in nearshore areas consists primarily of fine substrates so visibility may be near zero and collection may be primarily tactile (grubbing) - provide collected mussel to support staff for processing, and continue collections,
- travel back to boat launch and lodging.
Work occurred from early June to late-August 2019. Fathom Resources collected, sorted, identified, cleaned off zebra mussels, and relocated more than 173,000 freshwater mussels (Table 1). The three most abundant species account for 97.5 % of the total, with 77.5% Elliptio complanata, 14.2% Lampsilis radiata, and 5,8% Potamilus alatus. In addition to the 11 species previously identified from this reach of the river, three additional species were found (the last three species listed in Table 1), two of which are SGCN species.
Due to the success of this initial project year, field operations were repeated for 12-to-15-week periods, in both 2020 and 2021.
Table 1. Mussel species found in the reach of the Grasse River involved in the PCB remediation project. The species are arranged in abundance order:
Elliptio complanata (Eastern elliptio)
Lampsilis radiata (Eastern lampmussel)
Potamilus alatus (pink heelsplitter)*
Leptodea fragilis (Fragile papershell)
Pyganodon sp.
Pyganodon grandis (Giant floater)
Pyganodon cataracta (Eastern floater)
Utterbackii imbecillis (Paper pondshell) *
Ligumia nasuta (Eastern pondmussel) *
Lampsilis cardium (Plain pocketbook) *
Lampsilis sp. (L. radiata/L. cardium)
Strophitus undulatus (Creeper)
Alasmidonta undulata (Triangle floater)
Lasmigona costata (Fluted shell)
Ligumia recta (Black sandshell) *
Alasmidonta marginata (Elktoe) *
* SGCN species