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RESEARCH ARTICLE
Contents Vol 57(1)

Determining reproductive parameters for population assessments of chondrichthyan species with asynchronous ovulation and parturition: piked spurdog (Squalus megalops) as a case study

J. Matías Braccini A B C , Bronwyn M. Gillanders A and Terence I. Walker B
+ Author Affiliations
- Author Affiliations

A Southern Seas Ecology Laboratories, Darling Building DP 418, School of Earth and Environmental Sciences, University of Adelaide, Adelaide, SA 5005, Australia.

B Primary Industries Research Victoria, PO Box 114, Queenscliff, Vic. 3225, Australia.

C Corresponding author. Email: matias.braccini@adelaide.edu.au

Marine and Freshwater Research 57(1) 105-119 https://doi.org/10.1071/MF05076
Submitted: 26 April 2005  Accepted: 10 October 2005   Published: 17 January 2006

Abstract

Population assessments of chondrichthyan species require several key parameters of their reproductive biology, which were estimated for Squalus megalops (Macleay, 1881). Length-at-maturity differed depending on the criterion adopted for defining maturity. In the case of males, length-at-maturity was smallest when condition of seminal vesicles was adopted as a maturity criterion. For females, length-at-maturity was smallest when the largest follicle diameter >3 mm was adopted as the criterion for maturity; this was appropriate only as an indicator of the onset of maturity. Mature males are capable of mating throughout the year. Females have a continuous asynchronous reproductive cycle. The sex ratio of embryos is 1 : 1 and litter size and near-term embryo length increase with maternal length. Females have an ovarian cycle and gestation period of two years. This was reflected in the differences found between the maturity and maternity ogives. Although all females are mature at 600 mm, only 50% of them contribute to annual recruitment each year. Hence, for chondrichthyan species with reproductive cycles of two, three or more years, if maturity ogives are used in population assessments instead of maternity ogives, the models will overestimate recruitment rates.

Extra keywords: asynchrony, Australia, reproduction.


Acknowledgment

We are grateful to Peter Risley, Glenn Richardson and the crew of the fishing vessel ‘Nungurner’ for help in sample collection. This research was supported by an International Postgraduate Research Scholarship and a University of Adelaide Postgraduate Research Scholarship to JMB and an Australian Fisheries Research and Development Corporation grant (FRDC 2002/033) to TIW. BMG was supported by an Australian Research Council QEII Research Fellowship. Funding for the field and laboratory components was provided by Sea World Research and Rescue Foundation, Royal Zoological Society of New South Wales, Nature Foundation SA and Royal Zoological Society of South Australia.


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