Harwich Shellfish Laboratory and Environmental Factors

 

            The Shellfish laboratory located in Wychmere Harbor serves as a nursery for juvenile quahogs, Mercenaria mercenaria, for several months each summer.  They are grown in a semi-controlled environment with the use of upwellers.  Seed quahogs are placed in 18” diameter silo containers and seawater is actively pumped through them in order to deliver phytoplankton (food) to the growing clams.  Clams are filter feeders and as water passes between their gill filaments they trap phytoplankton on the surface of their gills.

            Success of an upweller system is due in part to several environmental factors which can be monitored and correlated to growth in the nursery.  Environmental factors which effect quahog seed growth include, but are not limited to, water temperature, salinity, and dissolved oxygen.  The Harwich shellfish laboratory has been in existence since 1994 and has been an excellent location to rear quahogs.  Since 1994, over 20 million quahogs have been reared in the shellfish lab.

 

Water Temperature:

            Quahog larvae have been grown successfully between 18-30°C.  Overall metabolic rate increases with temperature.  Water temperatures in the shellfish laboratory usually ranges between 17-26°C for the months of June-October.

 

Salinity:

            Salinity is most often measured in parts per thousand (ppt) and refers to the relative salt content in the water.  Quahog embryos develop optimally at 27.5 ppt and early-stage larvae cannot develop below 17 ppt.  The upper salinity limit for Mercenaria is 35 ppt.  The salinity inside the shellfish laboratory typically is between 30-33ppt.   The clams are rinsed with freshwater when the silos and tanks are cleaned.

 

Dissolved Oxygen:

            Oxygen is important in carrying out metabolic activities within the clam.  Well oxygenated seawater contains in excess of 5 milligrams oxygen per liter (5 mg/l).  Optimum growth occurs at concentrations above 4.2 mg/l oxygen and levels below 2.4 mg/l can impair growth.  Water within the shellfish lab is well oxygenated, due in part to high flow rates and water in the tanks having a large surface area exposed to the air.  Dissolved oxygen readings in the Wychmere shellfish lab run between 5.5 – 8.0 mg/l.

 

Conclusion:

            In summary, water quality within the shellfish laboratory certainly is conducive for growing quahog seed in the summer months.  Yearly variability including beginning seed stock size and quality as well as available phytoplankton densities throughout the summer have an effect on growth and success in the lab.   The public is welcome to visit the lab anytime – over 3,000 visitors have already enjoyed a trip to the lab.

 

** Environmental ranges were taken from The Northern Quahog, by Michael Rice, 1992.

 

Town of Harwich - Shellfish Nursery

Through the Years

 

1994:

 

·        First year of Shellfish Laboratory.

·        Culmination of two years of planning and development.

·        10 silos were in operation.

·        Started upweller with 280,000 quahog seed (avg. = 2mm).

·        Ended upweller season with 131,364 quahog seed (avg. = 6mm).

·        First and only year implementing plastic overwintering trays.

 

1995:

 

·        Laboratory upgraded to 30 silos.

·        Started upweller with 1,020,000 quahog seed (avg. = 1.0mm).

·        Ended upweller season with 537,993 quahog seed (avg. = 15mm).

·        County J-tech program lent assistance to maintain lab.

·        First and only year implementing hanging shellfish trays in Saquatucket Harbor.

 

1996:

 

·        Laboratory upgraded to 40 silos.

·        Started upweller with 2,000,000 quahog seed (avg. = 1.0mm).

·        Ended upweller season with 1,500,000 quahog seed (avg. = 13mm).

·        First year that seed was bedded down under protective mesh - Round Cove.

 

 

1997:

 

·        Laboratory upgraded to 59 silos.

·        Upgraded laboratory sea water pumps and service lines.

·        Started upweller with 3,000,000 quahog seed (avg. = 1.0mm).

·        Ended upweller season with 1,502,413 quahog seed (avg = 6.5mm).

·        Extended invitation to Brewster NRD to utilize extra lab space when available.

 

1998:

 

·        Laboratory maintained 59 silos.

·        Started upweller with 6,000,000 quahog seed (avg. = 1.0mm).

·        Ended upweller season with 5,294,500 quahog seed (avg. = 7mm).

·        First year for Harwich High school summer internship program.

·        Attempted five inexpensive, independent plastic upwellers in Saquatucket Harbor.

·        Brewster NRD deployed a floating upweller barge in Saquatucket Harbor.

·        Some quahog seed bedded down in wooden bottomless frames and mesh.

·        Began long term water quality database (Temp. Sal. and DO readings).

 

1999:

 

·        Laboratory maintained 59 silos.

·        Started upweller with 3,000,000 quahog seed (avg. = 1.0 - 1.5mm).

·        Ended upweller season with 2,767,000 quahog seed (avg. = 13mm).

·        Second year for Harwich High school summer internship program - 4 students.

·        Brewster NRD deployed a floating upweller barge in Saquatucket Harbor.

·        Continued long term water quality database (Temp. Sal. and DO readings).

·        Pilot study of 3,000 very small seed maintained by High School over winter.

 

2000:

 

·        Laboratory maintained 59 silos.

·        New intake boxes and screens built and installed.

·        Started upweller with 2,341,526 quahog seed (avg. = 1.5 - 2.0mm).

·        Ended upweller season with 2,238,750 quahog seed (avg. = 8mm).

·        Third year for Harwich High school summer internship program - 4 students.

·        No Brewster NRD deployed a floating upweller barge in Saquatucket Harbor.

·        Continued long term water quality database (Temp. Sal. and DO readings).

·        Had over 600 visitors to the lab - over 1500 total for past 3 years.

 

 

2001:

 

·        Laboratory maintained 59 silos.

·        New intake hoses and relocated connections near lab.

·        Started upweller with 2,200.000 quahog seed (avg. = 1.5 - 2.0mm).

·        Ended upweller season with 1,604,450 quahog seed (avg. = 11 mm).

·        Forth year for Harwich High school summer internship program - 4 students.

·        Continued long term water quality database (Temp. Sal. and DO readings).

·        Had over 500 visitors to the lab - over 2000 total for past 4 years.

 

2002:

 

·        Laboratory maintained 59 silos.

·        Painted interior of lab and gel coated tanks prior to season.

·        Started upweller with 2,760,000 quahog seed (avg. = 1.5 - 2.0mm).

·        Ended upweller season with 2,300,450 quahog seed (avg. = 8-9 mm).

·        Fifth year for Harwich High school summer internship program - 3 students.

·        Continued long term water quality database (Temp. Sal. and DO readings).

·        Had over 400 visitors to the lab - over 2400 total for past 5 years.

 

 

2003:

 

·        Laboratory maintained 59 silos.

·        Jim Coyle rebuilt barn doors for the lab.

·        Started upweller with 1,900,000 quahog seed (avg. = 1.5 - 2.0mm).

·        Ended upweller season with 1,532,670 quahog seed (avg. = 9 mm).

·        Sixth year for high school summer internship program - 3 students.

·        Continued long term water quality database (Temp. Sal. and DO readings).

·        Had over 350 visitors to the lab - over 2700 total for past 6 years.

 

 

2004:

 

·        Laboratory maintained 59 silos.

·        Painted interior of lab and gel coated tanks prior to season.

·        Roto-rootered the shellfish pipes/lines prior to growing season.

·        Larry reshingled portions of the lab and rebuilt bench.

·        Started upweller with 1,706,000 quahog seed (avg. = 1.5 - 2.0mm).

·        Ended upweller season with 1,503,000 quahog seed (avg. = 9-10 mm).

·        Seventh year for Harwich High school summer internship program - 3 students.

·        Continued long term water quality database (Temp. Sal. and DO readings).

·         Had over 380 visitors to the lab this year.