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Growth, reproduction and recruitment of the doughboy scallop, Mimachlamys asperrimus (Lamarck) in the D'Entrecasteaux Channel, Tasmania, Australia


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Zacharin, WF 1994 , 'Growth, reproduction and recruitment of the doughboy scallop, Mimachlamys asperrimus (Lamarck) in the D'Entrecasteaux Channel, Tasmania, Australia', Coursework Master thesis, University of Tasmania.

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The doughboy scallop, Chlamys (Mimachlamys) asperrimus (Lamarck, 1819) is
an abundant benthic bivalve mollusc found throughout south-eastern Australia. Large
populations of doughboys extend over wide areas in Bass Strait, and a commercial
fishery for the species has operated irregularly in the D'Entrecasteaux Channel in southeastern
Tasmania since the 1930's. This study describes the growth, reproduction and
recruitment of the doughboy scallop in the D'Entrecasteaux Channel in southern
Growth rates were observed from monitoring populations of scallops in natural
beds, reseeded populations, suspended culture and individual tagging. Values of Loo and
K from the von Bertalanffy model for a natural population were 94 mm and 0.578, and
for the suspended culture population, 105 mm and 0.573 respectively. Aging was
determined from external ring counts and von Bertalanffy growth curves. Observations of
ring formation in M. asperrimus suggest that the major external rings are formed due to
spawning stress. This is supported by the lack of a major ring in scallops < 40 mm that
have grown through a winter season but not spawned.
Histological studies of gonad development determined the various stages in
reproductive development. Males matured and released sperm e.arlier than females.
Gonads began early development in late March - early April and immature oogonia are
evident by May. Maturation continues through the winter months with a major spawning
event occurring in late September to mid October. A minor spawning may be observed in
December, but the significant decrease in GSI at this time may have been a consequence
of oocyte lysis and re-absorption. M. asperrimus has some reproductive development in
year 1 (0+) but the gonad does not mature past stage 3. Maturity is reached in the second
year (1 +).The smallest female observed with mature ova had a shell height of 57.5 mm.
The collection and identification of two hermaphroditic individuals during this study had
not been previously recorded for M. asperrimus.
Natural mortality estimates for M. asperrimus range between 0.23 to 1.04 yr-1 for
fully recruited year classes. Recruitment in M. asperrimus in the D'Entrecasteaux Channel
region is both spatially and temporally erratic. For the six year period during 1987 to
1992, settlement of juveniles was only significant in two years (1988 and 1990), with the
highest number of pre-recruits being observed in 1987.
Stock and recruitment parameters are discussed in relation to the change in
population dynamics of the M. asperrimus fishery in the D'Entrecasteaux Channel.

Item Type: Thesis - Coursework Master
Authors/Creators:Zacharin, WF
Keywords: Scallop culture, Scallops
Copyright Holders: The Author
Copyright Information:

Copyright 1994 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).

Additional Information:

Includes bibliographical references. Thesis (M.Sc.)--University of Tasmania, 1995

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