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The effects of a hydraulic dredge and adding shells on the environment and soft-shell clam population dynamics



This project aims to improve profitability of soft-shell clam farms in Atlantic Canada by increasing post-seeding survival rates, which has been demonstrated to be successful in US east coast quahog farming and Canadian west coast manila clam farming.

It has been demonstrated that:

  1. Hydraulic dredging enhances settlement and/or survival of quahogs. It will be important to understand the effects of mechanical harvesting on clams and the environment.
  2. The presence of adults or shells increases recruitment of juvenile bivalves. Thus, the addition of shells to the sediment may increase survival of juveniles.

The project seeks to compare the effects of hydraulic dredging and addition of shells to the sediment on the survival of juvenile soft-shell clams, and on the depth profile of physical and chemical parameters of the sediment (including grain size, sediment compaction, pH, carbonate/aragonite saturation states, and sulfides).

One of the concerns regarding mechanical clam harvesting is the release of buried organic matter and reduced metabolites. In the presence of oxygen, these become oxidized, thereby lowering the pH, which can reduce growth and survival of bivalves.

Adding shells to the sediment acts as a buffer by raising the pH and the saturation states, and has been shown to increase quahog and soft-shell clam recruitment. Results from this project (i.e. the addition of shells) may mitigate the potential negative effects of dredging. In addition, this project will provide insights related to the potential environmental effects from shelling activity on surrounding areas (habitats) which are currently not well understood.

Program Name

Aquaculture Collaborative Research and Development Program (ACRDP)


2015 - 2018

Principal Investigator(s)

Angeline LeBlanc
Aquatic Biologist, Fisheries and Oceans Canada
Gulf Fisheries Centre, Gulf Region

Collaborative Partner(s)

Marilyn Clark, Mills Seafood Ltd.

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