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Taking Stock: Researchers seek better estimates, understanding, of clams in Narragansett Bay

Rhode Island Sea Grant compares traditional clam stock estimates by dredging to estimates made using bull rakes

By Zoe Gentes, Rhode Island Sea Grant

Over 39 million clams were harvested from Narragansett Bay in 2012, supporting a $5.15 million commercial fishing industry. Estimates of clams in the Bay are used to set fishing limits. In Rhode Island, commercial shellfishermen use a bull rake for harvesting clams. The Rhode Island Department of Environmental Management (DEM), however, uses a hydraulic dredge to collect clams for population estimates. Fishermen say that the dredging method of harvesting is inefficient and inaccurate, and is likely to result in unnecessary limits on the commercial fishing operations.

Dale Leavitt, an associate professor of marine sciences at Roger Williams University, is conducting a study that compares the efficiency of dredge gear to that of a bull rake. He is going out on commercial shellfishing boats that are using bull rakes alongside DEM dredges to compare results. Being able to accurately take stock of clam populations in Narragansett Bay is important for making effective management decisions concerning commercial shellfishing. 

Understanding dispersal of quahogs, specifically, is of particular interest to researchers because quahogs do not move much once they settle as larvae. To better target harvesting efforts, “knowing where the quahog larvae move to is incredibly important for fishermen,” says Azure Cygler, an extension specialist from Rhode Island Sea Grant who is leading the R.I Shellfish Management Plan.

One management strategy is to create “spawning sanctuaries” by closing off areas and prohibiting fishing where large numbers of quahogs are located. However, if it isn’t known where the larvae will go, it is difficult to judge how effective the sanctuary may be in replenishing the Bay with quahog seed.

Leavitt and collaborators are using a hydrodynamic computer model called the Regional Ocean Modeling System (ROMS) to make an educated guess as to where the quahog larvae may be distributed when originating from a specific area. ROMS has been developed and calibrated against years of data with Sea Grant funding by Christopher Kincaid and David Ullman, researchers at URI GSO, to create a picture of how currents, circulation, and nutrients affect water quality in the Bay.

Kincaid, Ullman, and URI students can now use ROMS simulations to predict circulation and transport within the Bay under different conditions. By simulating quahog larvae in the ROMS program, including adding a larval behavior component, researchers like Leavitt can predict how the larvae will be dispersed by currents within the Bay under certain conditions. These predictions can help shellfishermen better understand where the quahogs are ending up, and what their populations might be.

 “The objective with our quahog management is to have the Bay produce enough quahogs to keep the fishing fleet economically viable,” Leavitt says. “In addition, quahogs are a part of the ecological fabric of the Narragansett Bay and therefore need to be managed in a way that keeps them as a functioning part of the ecosystem.”

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