Quantification of the maternal-embryo nutritional relationship of elasmobranchs: case study of wobbegong sharks (genus Orectolobus) in eastern Australia
Huveneers, C., Otway, N.M., Harcourt, R.G. and Ellis, M., 2011. Quantification of the maternal-embryo nutritional relationship of elasmobranchs: case study of wobbegong sharks (genus Orectolobus) in eastern Australia. Journal of Fish Biology, 78(5): 1375–1389.
The nutritional relationship between shark embryos and their mother has been relatively poorly studied. A review of the scientific literature identified several issues including the confusion over appropriate methods and misleading referencing that, when combined, suggested that previously proposed threshold values used to categorise the reproductive modes of some sharks might not be suitable. Standardised methods were then used to assess the threshold values in 236 ornate (Orectolobus ornatus) and 135 spotted (Orectolobus maculatus) wobbegong sharks collected from the commercial fishery in New South Wales waters. Two pregnant gulf wobbegong sharks (Orectolobus halei) were also obtained after the main sampling period had been completed. The three species exhibited similar reproductive cycles with pregnancies lasting 10–11 months. Embryos were first visible during January and external yolk sacs were fully absorbed by July when the embryos were about 200 mm long. Internal yolk sacs were first observed in April when embryos were about 160 mm long and persisted until birth. The total wet weight increased by 44–89% and 45–62% for the ornate and spotted wobbegongs, respectively, during development from egg to full-term embryo. In contrast, total organic weight decreased by 32–33% and 26% for the ornate and spotted wobbegongs, respectively. These results suggested that both species are strictly reliant on the initial yolk supplies in the egg with no additional nutrients supplied by the mother during pregnancy.