title: Living on the edge: latitudinal variations in the reproductive biology of two coastal species of sharks.
abstract: Differences in the reproductive biology of both the Australian weasel shark Hemigaleus australiensis and the Australian sharpnose shark Rhizoprionodon taylori were apparent between individuals from the southern-most extent of their range in eastern Australia (Moreton Bay) and those from northern Australia. For H. australiensis from Moreton Bay the total length (LT) at which 50% of individuals were mature (LT50) was 759 mm for females and 756 mm for males, values that were respectively 17-26% larger than reported for the species in northern Australia. The relatively low percentage (63%) of pregnant mature females and presence of small, similar-sized, embryos in utero in both May and November suggested a semi-synchronous, annual reproductive cycle in Moreton Bay, whereas a synchronous, biannual reproductive cycle occurred in northern Australia. It is likely that H. australiensis has a resting phase between gestation cycles at the southern-most extent of its range. For R. taylori from Moreton Bay the LT50s were 588 and 579 mm for females and males, respectively, values 2-3% larger than for individuals from the mid-Queensland coast and 31-35% larger than for individuals from northern Australia. The length at which 50% of the females were maternal (611 mm LT) in Moreton Bay was greater than the LT50, indicating that not all sharks mate immediately after maturing. Rhizoprionodon taylori in the south had an annual reproductive cycle incorporating a 7-8 month embryonic diapause, with pups probably born in February. A mean fecundity of 7·5 was almost double that reported from northern Australia. Regional variations in the reproductive characteristics of H. australiensis and R. taylori may influence their resilience to fishing and other anthropogenic pressures. The substantial differences reported here highlight the importance of region-specific life-history parameters to successful management and conservation.
authors.affiliation: Western Australia Fisheries and Marine Research Laboratories, Department of Fisheries Western Australia, 39 Northside Drive, Hillarys, P.O. Box 20, North Beach, WA, 6920, Australia. Steve.Taylor@fish.wa.gov.au.
authors.forename: S M
authors.initials: SM
authors.lastname: Taylor
authors.affiliation: Western Australia Fisheries and Marine Research Laboratories, Department of Fisheries Western Australia, 39 Northside Drive, Hillarys, P.O. Box 20, North Beach, WA, 6920, Australia.|Centre for Sustainable Tropical Fisheries & Aquaculture, College of Marine and Environmental Sciences, James Cook University, Townsville, QLD, 4811, Australia.
authors.forename: A V
authors.initials: AV
authors.lastname: Harry
authors.affiliation: School of Biomedical Sciences, The University of Queensland, St Lucia, Brisbane, QLD, 4072, Australia.
authors.forename: M B
authors.initials: MB
authors.lastname: Bennett
mesh_terms: D000818:Animals; D001315:Australia; D017753:Ecosystem; D047108:Embryonic Development; D005260:Female; D005298:Fertility; D005399:Fishes; D008297:Male; D011793:Queensland; D012098:Reproduction; D012741:Sexual Maturation; D012754:Sharks / Q000502:physiology*
keywords: Australia; Bergman's Rule; Carcharhiniformes; gestation; logistic regression