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Department of Planning and Natural Resources Division of Fish and Wildlife

Spatial and temporal variation in stock abundance of queen conch, Strombus gigas , in the US Virgin Islands. Research conducted by Gordon & Tobias. Department of Planning and Natural Resources Division of Fish and Wildlife. Biology of Queen Conch. About 3-3.5 years to reach sexual maturity

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Department of Planning and Natural Resources Division of Fish and Wildlife

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  1. Spatial and temporal variation in stock abundance of queen conch, Strombus gigas, in the US Virgin Islands Research conducted by Gordon & Tobias Department of Planning and Natural Resources Division of Fish and Wildlife

  2. Biology of Queen Conch • About 3-3.5 years to reach sexual maturity • Reaches 12 inches in length • Mature conch has flared lip • Lifespan as long as 20 years (Berg, 1987)

  3. Conch Reproduction • Mate during the warm summer months • Require at least 50 conch/hectare for reproduction (Stoner & Ray 1996) • Produce about 400,000 eggs per spawn • Spawn about 6 times a summer

  4. Conch Reproduction • Planktonic larvae stage (veligers) drift in water column for 2-3 weeks • Settle to the bottom and change into regular conch form

  5. Habitat & Feeding Habits • Commonly found in seagrass and algae habitat • Can be found in all habitats • Graze on various species of algae and seagrass • Reported to depths of 400 feet • Burying behavior (juveniles)

  6. Territorial Regulations in the USVI • Harvest size limits • -minimum length – 9 inches (23 cm) OR • -minimum lip thickness – 3/8 inch (9.5 mm) • Closed season extension* • June 1 – October 31 each year *In 2008 VI government extended seasonal closure by 2 months for the territory because of overfishing concerns on STX

  7. Territorial Harvest Quota • Recreational quota • -6 conch per day per recreational fisher • -maximum of 24 per boat per day • Commercial quota • -maximum of 200 conch per day per • registered commercial fishing vessel • No sale of undersized conch shell permitted

  8. Territorial Landing Restrictions • Landing quota developed in June 2008: • -50,000 lbs. annually per district • -Thereafter, the season will be closed until November 1 of that year. • All conch must be landed and reported in the district from which they were harvested. • Must be landed whole in the shell

  9. Total queen conch by fishing year. MSY is a range of 30,000 (CFMC) - 60,000 lbs (Olsen 2007). USVI MSY set at 50,000 lbs.

  10. Federal Regulations • Harvest size limits (9” length or 3/8” lip thickness) • Recreational limit= 3 conch per person or 12 per boat • Commercial limit= 150 conch per day • No hookah • Conch must be landed with meat and shell intact • No harvest in EEZ except Lang Bank, STX from October 1 – June 30

  11. Underwater Scooter Transects USVI = total of 52 sites/114 transects (STT=12 sites/28T; STJ= 12/24T; STX=30 sites/62T)

  12. Conch transect sites around St. Thomas/St. John, 2008-2009. Note: Two new sites were added to the original 22 based on fisher input.

  13. Conch transect sites around St. Croix, 2009-2010. Note: Eight new sites were added to the original 22 based on fisher input and areas of concern such as Lang Bank.

  14. 28 scooter transects around St. Thomas. *New sites based on commercial fisher input .

  15. 24 scooter transects around St. John.

  16. 62 scooter transects around St. Croix. *New sites based on commercial fisher input and areas of concern (Lang Bank).

  17. Area surveyed, number and density of adult, juvenile, and total queen conch observed on scooter transects, 2008-2010.

  18. Conch densities throughout the Caribbean determined by extensive surveys

  19. Note: Error bars are standard error

  20. Note: Error bars are standard error

  21. Note: Error bars are standard error

  22. Note: size at sexually maturity ~20cm (Stoner and Ray 1996)

  23. Lip Thickness: Juvenile = no lip, New adult =1-7mm, Adult (sexually mature) = 8-15mm, Old = 16-33mm, Very Old = 34-59mm. Maturity categories from Appeldoorn (1996) and Friedlander (1997).

  24. Only 10 sites/transects common to all survey years were used. Error bars are standard errors.

  25. Only 9 sites/transects common to all survey years were used. *Note: No juvenile data available for St. John in 1981 and 1985.

  26. Notes: (1) only adults were sampled in 1981; (2) only 16 of the 22 original transects were surveyed in 2001; (3) all 22 original sites were surveyed again in 2009

  27. Summary • USVI 2008-2010 overall conch densities are higher than previous years; however, adult densities <50 conch/ha. • Most juveniles were found in the 0-6m depth range, while most adults were found in the 25-30m depth range. Overall for USVI majority of the conch were in the 25-30m depth range. • Conch densities were greatest in seagrass habitat • Majority (>50%) of the conch found on scooter transects for USVI were sexually mature in terms of shell length (>20cm). • STX had the highest percent (%) frequency of sexually mature adults. STJ had the highest % frequency for old and very old conch, and STT and STX had the highest % frequency for juveniles.

  28. Questions???

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