Maximizing Trap Efficiency on Lummi Nation Estuarine Habitats to Reduce Ecosystem Impacts from Invasive European Green Crab
Since time immemorial, the nearshore habitats of the Salish Sea, the shared estuarine waters between coastal British Columbia and Washington State, have provided crucial habitats for many culturally important species: nursery areas for Dungeness crab, critical juvenile rearing areas for migrating Pacific salmon, and sedimentary deltas laden with clams and oysters. Together these animals form the basis of indigenous Salish People’s food sovereignty and help define their way of life. Yet today, these resources are at risk from the invasive European green crab (EGC), which was brought to the area under oceanic conditions exacerbated by climate change and is thriving due to the crabs’ ability to quickly adapt. The EGC is a pernicious burrower and a voracious predator of shellfish. Wherever the invasive species has become established, ecosystem calamity eventually follows; unless, that is, a timely management response and removal intervention occurs.
The EGC exhibits wide ranging tolerances for water quality parameters such as temperature and salinity. The species easily adapts to marshy, estuarine areas along susceptible shorelines. While intensive seasonal trapping has been shown to reduce the population of EGC established in marine environments, less is understood about the vulnerability to trapping of EGC in marshy, estuarine areas between terrestrial fresh and brackish waters.
In this project, researchers at the Lummi Nation trapped for EGC and simultaneously gathered water quality data (e.g., temperature and salinity) from selected marine habitats on their reservation and along transects between estuarine areas of the Lummi and Nooksack rivers. The spatiotemporal data was analyzed along these gradients and compared with trapping data collected from Lummi’s 750-acre marine aquaculture pond (positive “control” for EGC presence) to assess what approaches maximize trapping efficiency of EGC in brackish and freshwater habitats.
We found there was not clear correlation between the measured water quality parameters and green crab captures at the five sites trapped along Lummi River. This finding was likely due to low capture numbers of green crab on Lummi tidelands. But the ranges of salinity and water temperature across the gradient of Lummi River suggested green crab settlement upriver is possible. Exploratory trapping at three sites in the Nooksack River estuary resulted in no captured green crabs, likely due to the high freshwater output observed in spring and fall seasons, which likely prevented green crab movement into the system during the green crab larval dispersal phase. Based on our findings, we plan to prioritize and continue a regular trapping schedule along the Lummi River (e.g., weekly). But trapping in the Nooksack River will be less frequent (e.g., monthly).
Our project was successful in determining habitats to prioritize for EGC trapping on Lummi Reservation Tidelands. We were able to identify effective strategies in EGC monitoring and removal which will ultimately reduce threats to culturally important native species and ecosystems, and tribal food sovereignty. While this project was focused locally, the results are transferable to all tribal entities and natural resource managers along the coasts of Washington and Oregon that are facing similar challenges with EGC.
- Source: USGS Sciencebase (id: 6179aa59d34ea58c3c6fa26f)
Since time immemorial, the nearshore habitats of the Salish Sea, the shared estuarine waters between coastal British Columbia and Washington State, have provided crucial habitats for many culturally important species: nursery areas for Dungeness crab, critical juvenile rearing areas for migrating Pacific salmon, and sedimentary deltas laden with clams and oysters. Together these animals form the basis of indigenous Salish People’s food sovereignty and help define their way of life. Yet today, these resources are at risk from the invasive European green crab (EGC), which was brought to the area under oceanic conditions exacerbated by climate change and is thriving due to the crabs’ ability to quickly adapt. The EGC is a pernicious burrower and a voracious predator of shellfish. Wherever the invasive species has become established, ecosystem calamity eventually follows; unless, that is, a timely management response and removal intervention occurs.
The EGC exhibits wide ranging tolerances for water quality parameters such as temperature and salinity. The species easily adapts to marshy, estuarine areas along susceptible shorelines. While intensive seasonal trapping has been shown to reduce the population of EGC established in marine environments, less is understood about the vulnerability to trapping of EGC in marshy, estuarine areas between terrestrial fresh and brackish waters.
In this project, researchers at the Lummi Nation trapped for EGC and simultaneously gathered water quality data (e.g., temperature and salinity) from selected marine habitats on their reservation and along transects between estuarine areas of the Lummi and Nooksack rivers. The spatiotemporal data was analyzed along these gradients and compared with trapping data collected from Lummi’s 750-acre marine aquaculture pond (positive “control” for EGC presence) to assess what approaches maximize trapping efficiency of EGC in brackish and freshwater habitats.
We found there was not clear correlation between the measured water quality parameters and green crab captures at the five sites trapped along Lummi River. This finding was likely due to low capture numbers of green crab on Lummi tidelands. But the ranges of salinity and water temperature across the gradient of Lummi River suggested green crab settlement upriver is possible. Exploratory trapping at three sites in the Nooksack River estuary resulted in no captured green crabs, likely due to the high freshwater output observed in spring and fall seasons, which likely prevented green crab movement into the system during the green crab larval dispersal phase. Based on our findings, we plan to prioritize and continue a regular trapping schedule along the Lummi River (e.g., weekly). But trapping in the Nooksack River will be less frequent (e.g., monthly).
Our project was successful in determining habitats to prioritize for EGC trapping on Lummi Reservation Tidelands. We were able to identify effective strategies in EGC monitoring and removal which will ultimately reduce threats to culturally important native species and ecosystems, and tribal food sovereignty. While this project was focused locally, the results are transferable to all tribal entities and natural resource managers along the coasts of Washington and Oregon that are facing similar challenges with EGC.
- Source: USGS Sciencebase (id: 6179aa59d34ea58c3c6fa26f)