Current Drifters Don’t Match Belief N.Bay Flows Counterclockwise

In support on the Rhode Island Shellfish Management Plan (SMP), Rhode Island Sea Grant has dedicated its 2014-2016 research efforts in the areas of shellfish biology and the ecology of the resources that support shellfish and shellfish management.

Researchers have recently finished their first field season collecting data and will be processing this information over the winter months. Below are the latest updates for Sea Grant-funded projects.

– Updates from Quahog Migration Research –

It is suspected that parts of the Bay act as sanctuaries for adult clam spawning, others as settlement areas for the next generation of clams – both of which are important to the long-term sustainability of the species.

Drifter to measure surface current flow direction.

Drifter to measure surface current flow direction.

Scott Rutherford from Roger Williams University (RWU), in collaboration with Dale Leavitt (RWU) and Chris Kincaid and Dave Ullman from the URI Graduate School of Oceanography (URI GSO), are using the Regional Ocean Modeling System (ROMS) and Lagrangian TRANSport  (LTRANS) models to look at how water flows through Narragansett Bay and how it relates to quahog distribution when originating from a specific place.

Rutherford and his team developed drifters to mimic behavior of floating quahog larvae to get an idea of where they might end up based on the direction of the currents.

Over 30 drifters, both at 1 meter and 3 meters in length, were deployed from Ohio Ledge this past summer to get a sense of how different layers of the water column impact dispersal. All of the drifters were shown to end up somewhere in the East Passage of the Bay, which is contrary to general thinking that Bay circulation flows counterclockwise.

“The general idea is that the Bay circulates counterclockwise; water comes in the East Passage and flows out the West Passage. But we’re not seeing that happen with drifter tracks. Almost all of them go out the East Passage,” said Rutherford, noting that the drifters only indicate surface flow whereas the model is looking at the overall direction of circulation. “So is this a surface versus depth discrepancy? Or is it related to a particular time of year? It’s an interesting discrepancy.”


– Next Steps –

The team will be looking more closely at the tracks of each individual drifter and incorporate the wind vector to get a clearer picture of surface circulation patterns in the Bay. The team will also as well as incorporating data from 2007 and 2008, as well as 2014, into the ROMs model to get a range of environmental conditions, such as warming water temperatures, which impact larval behavior.

– Meredith Haas | Rhode Island Sea Grant Research Communications Specialist

For more research updates, please visit Rhode Island Sea Grant’s Research page