Negligible evidence for regional genetic population structure for two shark species Rhizoprionodon acutus (Ruppell, 1837) and Sphyrna lewini (Griffith & Smith, 1834) with contrasting biology
Ovenden, J.R., Morgan, J.A.T., Street, R., Tobin, A., Simpfendorfer, C., Macbeth, W. and Welch, D., 2011. Negligible evidence for regional genetic population structure for two shark species Rhizoprionodon acutus (Ruppell, 1837) and Sphyrna lewini (Griffith & Smith, 1834) with contrasting biology. Marine Biology, 158(7): 1497–1509.
The stock structure of two shark species commercially caught in north-eastern Australian and in Indonesian coastal waters, scalloped hammerhead (Sphyrna lewini) and milkshark (Rhizoprionodon acutus), were examined via DNA analysis. Australian samples were collected from a range of commercial fisheries operating in north-eastern Australian waters between Cape York, Queensland, and Laurieton, NSW, including the large-shark setline fishery of northern NSW. Although milkshark is not found in NSW waters, scalloped hammerhead comprises a small proportion of catches of large sharks in the NSW fishery. Knowledge about the stock structure of both species is important to ensuring exploitation of local populations is done sustainably.
Genetic analyses demonstrated that scalloped hammerhead caught in waters along the north-eastern coast of Australia were genetically similar to each other, and were not genetically dissimilar to animals caught in Indonesian waters, which was as expected based on previous studies of this species. Scalloped hammerhead are known to migrate large distances in some parts of the world – a feature that would explain these results.
Less expected were similar results along the eastern Australian coast for milkshark, which is a smaller, more bottom-dwelling, and less migratory species than scalloped hammerhead. However, these features are probably driving the genetic distinction that was found between Australian and central Indonesian milkshark populations.