Spatial and temporal variation in the reproductive biology of gummy shark Mustelus antarcticus (Chondrichthyes : Triakidae) harvested off southern Australia
Terence I. WalkerA Primary Industries Research Victoria, PO Box 114, Queenscliff, Victoria 3225, Australia.
B Department of Zoology, The University of Melbourne, Parkville, Victoria 3010, Australia.
C Email: Terry.Walker@dpi.vic.gov.au
Marine and Freshwater Research 58(1) 67-97 https://doi.org/10.1071/MF06074
Submitted: 3 May 2006 Accepted: 8 December 2006 Published: 2 January 2007
Abstract
Mustelus antarcticus, endemic to southern Australia, exhibits matrotrophic aplacental viviparity. Differences in synchronous ovarian and parturition cycles, mostly annual west and biennial east of longitude 138°E, are explained by environmental differences. Ovulation and parturition peak during November–December and the gestation period is ~12 months. Largest ovarian follicle diameter ranges from 15 to 28 mm at ovulation, and mean wet mass gain is 10-fold from in utero egg (~10 g) to full-term embryo (~100 g) at ~330 mm total length. The sex ratio of embryos in utero is 1:1, and litter size (1 to 57 embryos) rises curvilinearly with maternal length. Length-at-maternity and length-at-maturity increased with rising fishing mortality and subsequently decreased with falling fishing mortality. These patterns are explained by the hypothesis on the ‘phenomenon of apparent change of size-at-maternity’ (and size-at-maturity) caused by gill-net length-selective fishing mortality, which masks any potential density-dependent responses. Male length-at-maturity estimates from seminal vesicle condition, testis development and spermatogenesis stages are similar, but are less than estimates from clasper calcification. Maximum body mass of females is double that of males and, at any length >700 mm, mean body mass of females exceeds that of males.
Additional keywords: embryonic growth, fishery assessment, maternity, maturity, ovarian cycle, reproduction.
Acknowledgements
Acknowledgment is due to a large number of former and present staff of Primary Industries Research Victoria (PIRVic), or its predecessor organisations, who participated in field sampling of sharks and laboratory processing. These people are Alan Baxter, Barbara Baxter, Lauren Brown, Russell Hudson, Ian Knuckey, Peter Moulton, David Ramm, Stephen Saddlier and Megan Storrie. Anne Gason of PIRVic is acknowledged for advice on statistical analysis of data and application of the statistical package SAS, and Vladimir Troynikov of PIRVic is acknowledged for advice on description of the statistical models applied. The crew of FRV ‘Sarda’ and the many shark fishers who kindly provided accommodation, assistance, and hospitality aboard their fishing vessels are thanked. I am grateful to Ken Graham of New South Wales Department of Primary Industry for his thorough review of an earlier version of the manuscript and to Professor William C. Hamlett of the Indiana University School of Medicine for valuable discussions, particularly on appropriate terminology. Data were collected through three projects funded by the Fisheries Research and Development Corporation of Australia. These are FIRTA Project 1972/02 (Gummy shark investigations), FRDC Project 1985/104, and FRDC Project 1999/103.
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