Size and Age at Sexual Maturity of the Knobbed Whelk, Busycon carica Gmelin, 1791

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Size and Age at Sexual Maturity of the Knobbed
Whelk, Busycon carica (Gmelin, 1791)

• Christina J. Sellers
• Savannah State University
• Research Supported By the University of Georgia
  Marine Extension Service Skidaway Institute of
  Oceanography

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Classification, Distribution, and General Ecology

• Prosobranch molluscs of the family Melongenidae
• Found along the western Atlantic coast
• Prefer shallow depths, but tend to travel
  offshore during warmer months
• Diet Carnivorous (e.g. oysters, clams, etc.)

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Georgia Fishery

• DNR first authorized commercial harvesting in the
  1980s
• Dramatic increase in landings between the late
  80s to 90s
• On average 15-20 vessels each year
• Landings of 500,000 lbs. or 270,000 in monetary
  value
• Fishery season
• Crab-pots and intertidal handpicking

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Candidates for Overfishing?

• Low fecundity, slow growth, limited mobility, and
  long life span
• Currently no size limits
• Research is necessary to determine growth rates
  and size at sexual maturity in order to help
  conserve future stocks

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Materials and Methods

• South Shipping Channel of St. Simons Sound
• MAREX R/V Georgia Bulldog
• Gear 45 foot two seam balloon trawl net (4
  webbing)
• 1055 whelks were retained
• Size range 23-167 mm (shell length)

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Whelk Processing

• Measured for shell length, width and weight
• Extracted from shell and determined sex
• Operculum was removed
• To determine sexual maturity, tissue weight,
  penis/oviduct, and gonads were weighed
• Gonad and penis/oviduct indexes were calculated

S.L.
S.W.
S.L
S.W.
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Opercular Ageing

• Growth marks similar to fish otolith/scales
• Previous studies validated growth rings are
  annual
• Growth rings may not be consistent, therefore
  each was labeled clear, unclear, and unreadable
• Two methods dissecting microscope and also
  embedded into resin and sectioned

Ring 4
Ring 3
Ring 2
Ring 1
Nucleus
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Data Analysis

• Number of rings was related to sex and size
• von Bertalanffy growth parameters calculated
• von Bertalanffy growth curves for both sexes
• Reproductive indices were plotted against size
• Size range at sexual maturity visually determined
• Plotted size range onto von Bertalanffy growth
  curves (age at maturity)

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Results and Discussion

• Opercular rings versus shell length
• Age difference between sexes
• Reproductive indices plots
• von Bertalanffy growth curves

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What does the Future Hold?

• Size age at maturity relatively large and old
• Use of size limits questionable
• Would eliminate dockside culling
• Would allow whelks to reproduce before being
  harvested
• Result in solely targeting larger females

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Acknowledgements

• Savannah State University
• Skidaway Institute of Oceanography
• University of Georgia, MAREX, Shellfish
  Aquaculture Lab
• Alan Power, Ph. D.