John Kraeuter, "Clams (Quahogs) and Oysters: What drives the population?" Baird Symposium
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This document discusses population data collected for clams and oysters over many years in Delaware Bay and Islip, NY. Samples were taken annually using standardized methods to estimate abundance, recruitment, mortality, and other factors. The data show variations over time and space in key population metrics like recruitment, mortality, and how these relate to environmental conditions and harvesting levels. Managing shellfish populations sustainably requires long-term monitoring of these interrelated factors.
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John Kraeuter, "Clams (Quahogs) and Oysters: What drives the population?" Baird Symposium
- 1. Clams (Quahogs) and Oysters: What drives the population? Hard clam (Northern Quahog) (Mercenaria mercenaria) Infauna Eastern oyster (Crassostrea virginica) Epifauna Dr. John Kraeuter Marine Sci. Center - Univerisity of New England and Haskin Shellfish Research Lab. - Rutgers University
- 2. Delaware Bay
- 3. Islip Sampling • 6000 hectares divided into 400 grids • About 350 grids sampled annually • Duplicate 1.02 m2 clam shell bucket samples per grid • 6.4 mm mesh sieve, all live and dead enumerated and all live and dead measured • 25+ consecutive years of data
- 4. Delaware Bay Oyster Seed Beds 10ppt 28ppt
- 5. Delaware Bay Sampling • Oyster dredge • Random stratified design on each bed • Composite bushel of 3 1 minute hauls • Approximately 105 samples per year • All live and dead oysters counted and measured • Samples removed for disease and condition analysis • 50 + consecutive years of data
- 6. 800 Oysters/sq m 700 2009 2007 2005 500 2003 600 2001 1999 1997 1995 1993 1991 1989 1987 1985 1983 1981 1979 1977 1975 1973 1971 1969 1967 1965 1963 1961 1959 1957 1955 1953 Number m-2 Yearly and Average Oyster Abundance, Delaware Bay 900 Spat/sq m Mean oysters Mean spat 400 300 200 100 0
- 7. Yearly and Average Oyster Abundance, Delaware Bay 900 800 Boxes/sq m Oysters/sq m 700 Number m-2 600 500 Spat/sq m Mean boxes Mean oysters Mean spat 400 300 200 100 0
- 8. Yearly and Average Oyster Abundance, Delaware Bay 300 Boxes/sq m Oysters/sq m 250 Spat/sq m Mean boxes 11 Mean oysters90 150 Mean spat 68 100 50 2009 2007 2005 2003 2001 1999 1997 1995 1993 1991 1989 1987 1985 1983 1981 1979 1977 1975 1973 1971 1969 1967 1965 1963 1961 1959 1957 1955 0 1953 Number m-2 200
- 10. 75.5 75.4 75.3 75.2 75.1 39.5 39.5 UPPER 6.5 - 14.5 ppt Dermo – Low MSX – Very Low 39.4 39.4 UPPER CENTRAL 9.0 - 16.5 ppt Dermo – Moderate MSX – Low CENTRAL 14.0 - 20.0 ppt Dermo – High MSX – Moderate 39.3 39.3 LOWER 17.0 - 22.5 ppt 39.2 39.2 Dermo – High MSX – High 39.1 39.1 75.5 75.4 75.3 75.2 75.1
- 11. 0.30 Number per square meter 2000 0.25 1500 Mortality 0.20 0.15 1000 0.10 500 350 0.40 300 250 0.30 200 0.20 150 100 0.10 50 0 0.00 1953 1961 1969 1977 1985 1993 2001 2009 1957 1965 1973 1981 1989 1997 2005 1953 1961 1969 1977 1985 1993 2001 2009 1957 1965 1973 1981 1989 1997 2005 Oyster Spat Mortaltiy Oysters 300 0.50 Upper Central 0.40 600 0.30 400 0.20 200 0.10 0 0.00 Mortality 800 1953957961965969973977981985989993997001005009 1 1 1 1 1 1 1 1 1 1 1 2 2 2 Oyster Spat Mortality Spat Mortality 250 Number per square meter 0.60 1000 Number per square meter 0.50 400 0.00 1200 Central 450 0.05 0 0.60 Lower 0.80 0.70 0.60 200 0.50 Mortaltiy Upper 500 Mortality 0.35 Number per square meter 2500 150 0.40 0.30 100 0.20 50 0.10 0 0.00 1953 1961 1969 1977 1985 1993 2001 2009 1957 1965 1973 1981 1989 1997 2005 Oysters Spat Mortality
- 12. 900 0.45 MSX 800 0.40 600 DERM O 0.35 0.30 MSX 500 0.25 400 0.20 300 0.15 200 0.10 100 0.05 0 0.00 1953 1957 1961 1965 1969 1973 1977 1981 1985 1989 1993 1997 2001 2005 2009 Oyster Spat Mortality Mortality Number per square meter 700
- 13. Delaware Bay Seed Beds 8 Spat/adult 7 Mean spat/adult 6 Spat/Adult 5 4 3 2 1 0
- 14. 2011 2010 2009 2008 2007 2006 2005 2004 2003 2002 2001 2000 1999 1998 1997 1996 1995 1994 1993 1992 1991 1990 1989 1988 1987 1986 1985 1984 1983 1982 1981 1980 1979 1978 1977 Number m-2 Islip Hard Clam Population 6.5 6 5.5 5 4.5 4 3.5 3 2.5 2 1.5 1 0.5 0
- 15. Harvest as a percentage of potential recruits 350 325 300 1 Year Old 2 Year Old 275 250 Percent 225 200 175 150 125 100 75 50 25 0 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000
- 16. Islip Clam Population 5 4.5 Harvestable 4 Seed Mean Harvestable Number m-2 3.5 3 2.5 2 1.5 1 0.5 0 Mean Seed
- 17. Islip, New York 0.25 Age 2 Seed per adult 0.2 0.15 0.1 0.05 0
- 18. 2004 2003 2 2002 2.5 2001 3 2000 1999 1998 1997 1996 1995 1994 1993 1992 1991 1990 1989 1988 1987 1986 1985 1984 1983 1982 1981 1980 1979 1978 1977 Number per sample Islip New York 3.5 Live Dead Recruits Mean Live 1.5 Mean Dead.0.26 0.36 Mean Recruit 1.5 1 0.5 0
- 19. 2004 2003 2002 2001 2000 1999 1998 3.5 Harvestable 2 0.25 1.5 0.20 0.15 1 0.10 0.5 0.05 0 0.00 % Mortality 2.5 1997 3 1996 1995 1994 1993 1992 1991 1990 1989 1988 1987 1986 1985 1984 1983 1982 1981 1980 1979 1978 Number Islip Hard Clam 0.45 0.40 Recruit 0.35 % Mortality 0.30
- 20. Summary • Managing shellfish populations cannot be done without basic population data collected on a regular schedule that is scaled to be in concert with the factors controlling the population. • Standing stock is important but used alone it is a misleading indicator for managing the resource. • All population measurements should include BOTH a recruitment and a mortality estimate. • If the population is arrayed over a salinity gradient the processes controlling the population may vary along the gradient. Just because an area has high recruitment or good growth does not a priori mean that the spot is a good place to begin a restoration program. • Sustainable fishing requires that the removal rate be based on the relationship between recruitment and mortality and NOT on standing stock. • Too much effort is aimed at evaluating recruitment and not enough is directed to finding better ways of measuring mortality.