Sharks fear killer whales. How does this impact the ecosystems they share?
- A new study finds that sharks will flee areas they met orcas in for up to a year.
- Killer whales are known to eat sharks, but it is unknown if the sharks are fleeing because they know that too.
- The discovery will change our understanding of how marine ecosystems evolve.
The true apex predator<p>The study, titled "Killer whales redistribute white shark foraging pressure on seals," results from years of investigations into the movements and behavior of 165 tagged great white sharks, observations and records of killer whale movements, and information on seal populations off the coast of California. They also looked to previous descriptions of shark and whale interactions to give context to their findings.</p><p>The sharks immediately turned tail and fled in every time they crossed paths with orcas. They'd also stay away from that place long afterward. Only <em>one </em>observed shark dared venture back to where it had just encountered the whales, and it didn't stick around. Most of the sharks merely fled a bit further up the coastline, while others went much further out to sea to avoid the whales. </p>
Why are they doing this?<span style="display:block;position:relative;padding-top:56.25%;" class="rm-shortcode" data-rm-shortcode-id="14ccb270e8cc6888b69118539a29b63b"><iframe type="lazy-iframe" data-runner-src="https://www.youtube.com/embed/B7GHCJXwLw8?rel=0" width="100%" height="auto" frameborder="0" scrolling="no" style="position:absolute;top:0;left:0;width:100%;height:100%;"></iframe></span><p>Orcas have been known to eat great whites. The remains of the sharks are a grotesque sight to behold and are always missing their <a href="https://www.nationalgeographic.com/animals/2019/07/killer-whales-orcas-eat-great-white-sharks/#:~:text=By%20Emma%20Rigney&text=In%20October%201997%2C%20tourists%20in,killer%20whales%20eating%20white%20sharks." target="_blank">livers</a>, no matter how much else remains or is missing. If the orcas have discovered a source of Chianti to pair with them or not remains unknown at this <a href="https://youtu.be/bHoqL7DFevc?t=28" target="_blank">time</a>.</p><p>However, we don't currently know if the sharks are fleeing because they understand that risk, because they knew the orcas would fight them for the same food supply, because whales look big and scary to them, or some combination of the three.</p><p>Before this gets too frightening, there are no known cases of wild orcas killing <a href="https://en.wikipedia.org/wiki/Killer_whale_attack" target="_blank">humans</a>, and only a few examples of injuries being caused by these interactions. <a href="https://bigthink.com/surprising-science/orcas-and-stress" target="_blank">Orcas kept in tiny boxes</a> for long periods can be a bit more violent, but that's another story. </p>
Nuclear weapons, whale sharks, and how to use both to make eco-tourism more sustainable.
- Scientists have finally determined the age of whale sharks using radioactive elements from bomb tests.
- Using the new data, the age range of the animals' bones has now been determined.
- The findings will help conservationists better maintain whale shark populations.
Majestic whale sharks, the gentle giants of the shark family.<p>Weighing in at 9 tons (20,000 pounds) and typically growing to around 10 meters (32 feet) long, the <a href="https://en.wikipedia.org/wiki/Whale_shark" target="_blank">whale shark</a> is the largest living species of fish. Despite the name, it is not a whale, though it is the size of one. Like many kinds of whales, it filter feeds on plankton.</p><p>Many things about the whale shark have remained unknown to science; how long they can live, their mortality rate, and how exactly to determine the age of a specimen from its remains was chief among them. However, these questions are now a little closer to being settled. In a <a href="https://www.frontiersin.org/articles/10.3389/fmars.2020.00188/full" target="_blank">study</a> recently published in <em>Frontiers in Marine Science,</em> scientists explain how they were able to date the bones of two whale sharks who met their fate earlier than they may have expected. </p><p>Like trees, whale sharks' bones have growth rings. Scientists have known about these rings for a while, but how quickly the rings grow has been unknown. It is difficult to use them to estimate the age of a shark if you aren't sure how much time each ring represents.</p><p><br></p>
A whale shark vertebra from Pakistan, in cross section, showing 50 growth bands
Image: © Paul Fanning, Pakistan node of the UN Food and Agricultural Organisation<p>This is where carbon-14 comes in. As a result of nuclear bomb tests during the Cold War, large quantities of carbon-14 were put into the oceans. The isotope slowly made its way up the food web and into the bodies of larger animals. Knowing the yearly changes in the amount of carbon-14 in the oceans due to bomb testing, scientists merely had to compare that data with the changes seen in the sharks' bones.</p><p>"We found that one growth ring was definitely deposited every year," <a href="https://www.eurekalert.org/pub_releases/2020-04/aiom-cwn033020.php" target="_blank">said Dr. Mark Meekan</a> of the Australian Institute of Marine Science in Perth, a co-lead on the study. "This is very important, because if you over- or under-estimate growth rates you will inevitably end up with a management strategy that doesn't work, and you'll see the population crash." This means the sharks used in this study were around 35 and 50 years old at the time of their deaths.</p><p>Working forward from there, the scientists were able conclude that the animals may have an age range of 100-150 years. "Earlier modelling studies have suggested that the largest whale sharks may live as long as 100 years," Dr. Meekan explained in <a href="https://www.eurekalert.org/pub_releases/2020-04/aiom-cwn033020.php" target="_blank">a statement</a>. "However, although our understanding of the movements, behaviour, connectivity and distribution of whale sharks have improved dramatically over the last 10 years, basic life history traits such as age, longevity and mortality remain largely unknown. Our study shows that adult sharks can indeed attain great age and that long lifespans are probably a feature of the species. Now we have another piece of the jigsaw added."</p>
The relatively quick evolution of nine unusual shark species has scientists intrigued.
- Living off Australia and New Guinea are at least nine species of walking sharks.
- Using fins as legs, they prowl coral reefs at low tide.
- The sharks are small, don't be frightened.