THERE have been three shark attacks in Sydney waters over the last three weeks, but there is no agreement as to whether shark numbers are on the increase – or not.
According to NSW Deputy Premier, Carmel Tebbuts, there is no evidence of increased shark numbers in NSW but Ms Tebbuts does admit cleaner waterways around Sydney (via SMH).
According to the Department of Primary Industries chief scientist, Steve Kennelly, because waters are cleaner there are more sharks. Hang on! This is not what the Deputy Premier said.
Professor Kennelly explained we are seeing a healthy ecosystem, “to the point where we’re getting whales underneath the Sydney Harbour Bridge and … lots of good bait fish coming in, tailor, king fish and so on and sharks feed on those things (via ABC).
Professor Kennelly did not mention that there have also been bans on commercial fishing in Sydney Harbour since a dioxin scare in January 2006 – this would also probably mean more fish.
According to Professor Kennelly not even new bans on hunting sharks (due to new fishing quotas) will impact on the risk of shark attacks (also via ABC Online).
Let’s summarize, sharks eat fish, so if there are more fish you might expect more sharks, add to this, new bans on hunting sharks, so again expect more sharks. More sharks might increase the risk of shark attacks. “Nah”, suggest some bureaucrats and politicians!
Wouldn’t it be better if government admitted that policies intended to increase the numbers of fish and sharks, are having an effect, and so the risk of shark attack could increase – and then explain how to mitigate like not swimming at dawn or dusk.
Jennifer Marohasy BSc PhD is a critical thinker with expertise in the scientific method.
Although it is difficult to draw any conclusions about overall numbers of sharks from three attacks, cessation of commercial fishing should be expected to substantially increase shark numbers. Maximum sustainable yield in most fisheries is attained at a population size of about one-third or less than that of an unexploited population. When commercial fishing ceases, populations of exploited species usually rebound quickly and shark numbers can be expected to follow those of their prey.
In addition, sharks are generally much slower growing than most bony fishes and they are vulnerable to considerable fishing mortality as bycatch even if not targeted. Everything considered, it seems probable that the shark population around Sydney should be expected to substantially increase as the result of no commercial fishing.
Up here in north Queensland we have a similar situation with crocodiles but have learned to live with them. Like us, Sydney will just have to accept regular human sacrifices as Gaia requires.
Jen,
I thought you had a greater respect for your reader’s intelligence…. Sigh….
What are you saying here? The ministers are mincing words? The ministers are misleading? The ministers are not shark experts?
As a scientists yourself Jen, and the proprietor of one of the ‘very best environmental blogs on the planet’, surely you will wait for actual surveys to be conducted before you go speculating on whether shark numbers have increased or not, or whether the existing shark populations are taking advantage of warmer ocean temps, more bait fish, and more humans taking a dip in what is essentially their domain??
Travis,
I am looking for the best survey data …
Any pointers? But no white pointers, please.
>But no white pointers, please.
I believe these animals are now referred to as white sharks Jen, but if it suits your ‘flakey’ joke, so be it…
The ABC, SMH and others will also no doubt quote ministers etc as saying surveys need to be done as this data is lacking. So my guess is that there is no ‘best survey data’, which is hardly surprising really.
If you want to know the truth,speak to fisherman.We have made the waters cleaner and established lots of marine reserves.Sharks are breeding and nibbling on a few humans.The NSW State Govt will now increase the shark quota that fisherman can take to save our tourist industry.The poms have fainter hearts than ours.Our intrepid surfers will not stop their life’s desire.It will mean more waves for the brave.
We are presented with statistics that show a very remote chance of being eaten,but if you are one of the few who often surf ,which excludes the millions who don’t,your chances of being taken are greatly enhanced.Don’t believe raw statistics.
The spearfishers have been monitoring shark numbers for that past couple of years and they say the numbers are increasing in a letter to the SMH today.
http://www.auf-spearfishing.com.au./
Shark attacks blamed on growth in fish stocks, says the Australian on March 5:
STRICT fishing regulations may have contributed to Sydney’s record of shark attacks, with predators lured into shallow water by an abundant supply of kingfish, salmon and other fish.
NSW has the highest number of recorded shark attacks and the nation’s tightest restrictions on fishing for sharks. Victoria, by contrast, has recorded only a fraction of the shark attacks and no annual quota on the number of sharks that can be caught.
In Queensland, the head of the state’s commercial fishing peak body, Neil Green, warned that tighter fishing regulations and an annual reduction in the state’s shark catch could lead to more shark attacks.
“I don’t think we should just allow sharks to get out of hand in numbers,” he said.
According to shark experts, an increased food supply created by commercial fishing restrictions, intended to protect fish stocks, could help explain why three shark attacks had occurred in as many weeks in Sydney waters.
Taronga Zoo shark expert John West said that shallow waters around Sydney contained “seemingly large schools of bait fish, attracting larger predators like kingfish and salmon, which in turn are attracting the sharks”.
“The number of shark attacks doesn’t mean there are more sharks around, per se, but they’re localised on the feeding schools,” Mr West said………
http://www.theaustralian.news.com.au/story/0,25197,25140732-5013404,00.html
Try this link:
http://www.aussmc.org/Shark_attack_Sydney.php
Dave