NMAI 2002

Project: Ecological characteristics and carrying capacity of suspended shellfish culture systems

The Pacific Shellfish Institute’s Mussel Project

Selected Bullets

1. Presented preliminary study results: “Ecology of Mussel Farming in the Puget Sound” at the Pacific Coast Shellfish Grower’s Association-National Shellfish Association’s (Pacific Coast Section) annual meeting in Newport, OR in September 2002.
2. Completed between November 2001 and October 2002 research of the growout cycle at a large commercial mussel farm in Totten Inlet, south Puget Sound, WA.   The farm site consists of 8 rafts each made up of 6 individual units with a total annual production of about 500,000 lbs.   We completed current and water quality measurements; phytoplankton sampling in and through the culture system; feeding and sedimentation studies; sampling for changes in mussel size and weight; and underwater video and benthic surveys.  A similar suite of observations began in early 2003 at a mussel farm in north Puget Sound 

Preliminary findings on how intensive mussel culture affects the water column and benthic community:

1. Water currents are decidedly lower within the mussel culture system than at control stations, current direction fluctuates rapidly on the down-current end of raft units (dependent on tidal direction), and varies in speed and direction with water depth.
2. Phytoplankton densities decrease markedly as water flows through the mussel culture system due to uptake by the mussels and removal as “pseudo-feces.”   However, within 3 to 6 meters downstream (in the tidal current) plankton levels recover to the same densities seen at upstream control stations.  
3. Water clarity increases as it moves through the raft system, with the clearest water in the center to down stream end of the raft.  Clarity decreases rapidly as water moves downstream and mixes in eddies created by raft system. 
4. Mussel growth (shell length and weight) mirrors the seasonal trends in phytoplankton densities, and was significantly greater on the portion of the raft system facing the entrance of the inlet.  However, there was little variation in mussel growth within individual raft units – mussels grew at about the same rate in the middle of the raft as around the edges.
5. Sediment deposition attributed to mussel culture is largely limited to the footprint of the raft units with little or no sediment effects outside the immediate culture area