If you reside along Australia’s east coast, you know spring time spells wild water temperatures and sharks make their appearances more frequently.
Up today, down tomorrow is usually the trend. No wonder they dubbed it a “spring suit”. And considering that La Niña is already here with us, 2020 feels even more awkward than usual.
The latest shark attack in Port Macquarie earlier this week have left many wondering whether the changes in the watery climate had any impact on the behaviour and movement of sharks.
But lol! As you ponder over that, a new study on this subject just popped up—and it’s quite interesting. Funded by the NSW DPI fisheries department through the Shark Management Strategy, the study evaluates whether or not environmental factors like wind, water temperatures, waves and tide activities influence the actions of white sharks off the eastern Australian coastlines.
What Did Researchers Find?
The team of researchers consisted some of the notable hitters including three expert scientists associated with the DPI: Paul Butcher, Craig Brand and Chris Gallen. And their conclusion? A resounding NO, not really.
The scientists examined data from 444 white sharks featured in the drumline program off New South Wales for a period of four years starting late 2015 to 2019. Transmitters that could be detected by Smart Buoy array off the NSW coast within a distance of 500m were fitted to all the sharks. 87% of the shark dataset consisted of juvenile sharks with near babies and sub-adults included in the mix. Data was carried out according to specific time of day and month, tide, water temps, lunar phase and swell height.
By a significant number, the most individual shark detection were actually off Forster. A small number were spotted off the South West Rocks and in Crescent Head. Many hits appeared off Hawks Nest but these were mostly by five sharks who kept hitting the receiver.
Sharks were seen to be more active during the day, with peak time being at 11am and less active at surf two metres or more. The sharks were also less active during troughs and tidal peaks but more active during full moons. Activity was at its peak when the water temperature ranged between 18-24 degrees, meaning most times they were off this coast.
Generally it appears that fluctuations such as these have little if any effect on the behaviour or numbers of sharks over time. This is besides time of the year for which the authors refer to as a “strong seasonal variation”.
Numbers were highest in September and a decline for the period between October and April. The report says in part. “The bulk of the total variation in detection data (~79%) remained unexplained by our model.
“We found that the deviance explained by temperature was only 17% of the deviance explained by the temporal factor ‘month’, suggesting that other environmental factors, not accounted for in this study, are driving seasonal variation.”
Could this include food or perhaps whale migration? Well, this is worth a study, of course in another research.
But as it is often the case with these kinds of research papers, it’s those small details around the edges that hit hard. This is mainly because they incorporate data that the DPI has never made available to the public.
For example, of the 444 white sharks whose SMART drumline tag data is featured in the study, 75 of them had been caught twice with 7 being caught thrice and three having hit a drumline four times.
This means about 20% of white sharks aren’t adequately stopped by the drumline experience to keep off in future and a minute number seems not to give a damn whatsoever.
In addition, once the sharks are tagged, they can be individually identified by the receiving buoy. Yet this info—shark type, size, gender etc. is not captured anywhere on the shark app alerts received daily on your mobile phone. You may be able to tell if it’s a 1.5m semi-baby white shark or a 3.0 metre super-predator. Unfortunately you can’t. And why not?
Moreover, the receivers are questionable too and the study explains in part “receiver performance showed an optimum between 17 degrees C and 20 degrees C, followed by a drastic decrease in detection efficiency”.
Notably, shark activity in waters above 20 degrees are “likely much higher” than it’s indicated in the study.
Does it mean that SMART buoys are unreliable in waters that are above 20 degrees? That can make for really exciting news for surfers in northern Ulladulla who rely on the app alerts for the latest updates or information, particularly in any La Niña year.
Additionally, the study was conducted in the context of the Australian Environment Protection and Biodiversity Conservation Act of 1999. The legislation lists white sharks as “threatened”.
If you’re in the mood for more, check out the research paper yourself.
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