Southern Australia’s sharks and rays face mounting threats as warmer waters push more tropical species southwards and habitats change, exacerbating threats to critically endangered species.
A study aimed at identifying the risks to some 132 different species found in waters ranging from south-west Western Australia to NSW has been published in the Fish and Fisheries journal. It seeks to give authorities a method to prepare for the threats of overfishing and climate change.
“This is the first time we’re actually bringing them together as a risk assessment,” said Terence Walker, a research fellow at both Melbourne and Monash universities and lead author of the paper. “The challenges for fisheries managers are growing all the time.”
While tighter controls on commercial fishing since the early 2000s had arrested the decline of many shark, ray and chimaera species such as elephant fish, those gains could be eroded as more tropical species such as tiger and bull sharks extend their ranges southwards, the researchers said.
The East Australian Current, which shifts tropical water southwards, is strengthening and making the Tasman Sea one of the world’s warming hot spots as sea-surface temperatures rise at about four times the global rate. The Leeuwin Current, which flows south along the WA coast, is also strengthening although not as rapidly as its eastern counterpart.
“Global warming is literally going to push southern sharks and rays into a corner, because they can only go so far south and west,” said Leonardo Guida, a shark scientist with the Australian Marine Conservation Society and a co-author of the paper. “Everything points to an urgent need to rapidly adjust how fisheries work.”
The paper also found that at present fishing levels, as many as six species already assessed as endangered including the school shark and maugean skate will have their recovery hampered by southward-migrating rivals.