Fact Sheet

Research: Impacts of Hydraulic Shellfish Harvesters

Impacts of Mechanical Harvesting of Shellfish

Friends of the Bay is currently researching the scientific literature available on the environmental impacts of mechanical shellfish harvesters.  Links to the most relevant papers we have found to date can be found below.

In its Bayville hatchery, Frank M. Flower and Sons  reports that they annually raise approximately 100 million juvenile clams and oysters which are then “planted” on the portion of the bay bottom which the farm leases from the Town of Oyster Bay.

As these juvenile shellfish grow, they are periodically sorted and transplanted to other leased areas of the harbor. Ultimately, after 2-3 years of growth, the clams and oysters are harvested for market.

Frank M. Flower and Sons uses  hydraulic harvesters to bring their shellfish from the bottom to the surface. Recently the North Oyster Bay Baymen’s Association has raised questions about the environmental impacts of these mechanical harvesters.

Mechanical and hydraulic shellfish harvesters are often referred to as “dredges.” It is important to note that there are significant and substantial differences in scope and impact between ‘shellfish harvest dredging’ and ‘channel dredging,’  which is used to permanently remove huge quantities of bottom material to deepen channels and allow passage of larger ships. The two processes should not be confused.

Frank M. Flower uses two different kinds of harvesters. One is a metal rake and basket fitted with water jets which loosen the top few inches of bottom mud so the clams are caught in the basket. The second type is a pump which ‘vacuums’ the surface of the bottom, bringing oysters (and other unattached organisms and material) to the surface where it is sorted, with unwanted by-catch returned to the water.

Links to the Most Relevant Papers Found to Date

1.) NOAA Technical Memorandum NMFS-NE-220: Review of the Ecological Effects of Dredging in the Cultivation and Harvest of Molluscan Shellfish. (A review of some 200 papers on the subject.)


2.) Review of the Environmental Impacts Related to the Mechanical Harvest of Cultured Shellfish. (Prepared for the Suffolk County Shellfish Aquaculture Environmental Impact Study, 2008. )


3.) Effects of hydraulic shellfish dredging on the ecology of a cultivated clam bed. NOAA Fisheries, Northeast Fisheries Science Center, Milford Laboratory, Milford, CT.


4.) Literature Review: Ecological Impacts/Benefits of Dredging for Shellfish; Maryland Department of Natural Resources.  (Abstracts and Links to scores of papers, sorted by target species.)


5.) Effects of hydraulic dredging on the benthic ecology and sediment chemistry of a cultivated bed of the Northern quahog, Mercenaria mercenaria. NOAA Fisheries, Northeast Fisheries Science Center, Milford Laboratory, Milford, CT.

Effects of hydraulic dredging on benthic ecology…