Nowhere has the fraught and complex relationship between surfers and sharks played out with as much drama as at Réunion Island, a department of France situated in the Indian Ocean off Madagascar. A surfers’ paradise, the island has seen a succession of gruesome attacks by bull sharks on surfers. A decision was made in August 2012 to cull sharks around the island, which was almost immediately reversed as it contravened French law (the sharks are in a Marine Protected Area, where hunting is forbidden).
An article at GQ.com describes the attacks and the community response, and attempts to understand the reason behind the sudden increase in human-shark interactions. It is interesting, as someone outside surfing culture, to get an insight into the impact of these events on the local surfing community. One can sense the frustration and bewilderment of the surfers, particularly because the explanations for increased shark sightings and bites on humans are hard to grasp.
Frédéric Buyle, a Belgian free diver and shark conservationist, even went so far as to theorise that
… bull sharks’ social units are complex enough that the loss of a single individual could send a group into a tailspin of erratic behavior. It’s also possible, Buyle posits, that if an influential individual were to be injured, the others might help it hunt for easy prey—and nothing could be easier prey than an oblivious land mammal on the surface. It’s a leap of imagination to see the tragedy of the attacks in reverse perspective: a beloved bull (do they love one another?), suddenly wrenched from the water, vanishing into the sky; the grieving survivors (do they grieve for one another?) rallying together, making a necessary change.
It’s important to remember that Buyle isn’t a scientist; he has, however, been passionately involved in the events at Réunion, and writes more about them here (in French – use Google translate).
Christopher Neff writes at Save Our Seas and for The Conversation on the emotive issue of shark hunts and culls. While they satisfy our desire for vengeance on the animal or animals that may have bitten water users, there is no scientific evidence that they work. This excellent article on tiger sharks off Hawaii highlights the same point.
I’ve been appallingly tardy in writing about this talk, but recent events in False Bay have reminded me that my notes have been sitting waiting for me to attend to them for several (ahem) months. My diary indicates that the series of talks that it was part of was held in November 2012. Dr Barnett has in fact left South Africa and returned during the time it’s taken me to get to this task. Sorry.
Broadnose sevengill cowsharks (Notorynchus cepedianus) are part of the order Hexanchiformes, which comprises six species. This is a primitive order of modern sharks with six or seven paired gill openings (most sharks have five). Four species are cowsharks, and the others are deep water sharks.
Surprisingly little is known about sevengill cowsharks, but Dr Barnett contends that they should be an extremely important apex predator. They are found worldwide, but not (so far) in the north Atlantic. There are far more of them than there are white sharks, and they eat the same sort of things: fish, rays, seals, and other sharks. Their role in coastal ecosystems is very important.
They are found in coastal waters of countries including (but not limited to) Australia, South Africa, Argentina, and California. There are known nursery areas at the latter two locations. Only one pregnant female has been dissected. She was carrying 82 pups (for context, white sharks bear 2-10 young, hammerheads about 50, whale sharks up to 300, and most other shark species 2-40). Their reproductive cycle is thought to be about two years in length. It is not known at what age these sharks reach sexual maturity.
Video still of the hooked cowshark
Sevengill cowsharks are on the IUCN Red List as data deficient (not enough is known about their conservation status). The IUCN Red List website page about the sevengill is informative. They are a target species for recreational fisheries (we often see specimens with hooks stuck in their mouths when we dive at Shark Alley), and a low value bycatch species for commercial fisheries in South Africa. There are several semi-commercial fisheries elsewhere that target them. There is some evidence that the fisheries in California and Namibia are not sustainable.
Tasmania study
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For some time, Dr Barnett has been studying the sevengill cowshark population found in the south eastern corner of Tasmania, in the system of bays that makes up the Derwent River estuary. The water here is turbid and there is a wedge of salt water that moves up and down the river with the tide. The river is at most 40 metres deep, and Norfolk Bay is about 20 metres deep. The winter water temperature in the area is 8-13 degrees, and in summer the maximum water temperature is 21-22 degrees. Much like False Bay (except for the river)!
The estuary is a shark refuge area and also includes populations of soupfin and smoothhound sharks, which pup there. The aim of the study has been to determing the population structure, abundance, diet, habitat use, and predator-prey relationships of the cowsharks.
Barnett fished for sharks using long lines with 50 hooks per line, deploying four lines per night. He tagged and released 457 sharks in total, took biological samples and measurements, determined their sex, and flushed their stomachs to see what they’d been eating. Sixteen percent of the females had mating scars (bite marks). He found more sharks each year in summer, and fewer in winter. Do they leave? Or do they not get caught in winter? Of the 457 sharks tagged, 68 (15%) were recaptured, in the same bay as where they were first caught.
Cowsharks are about 50 centimetres at birth, and after a year they are 70-80 centimetres long. The Derwent estuary is not a pupping or nursery ground, based on the measurement distribution that Barnett observed. He caught 60-100% female sharks (depending on what time of year he fished), averaging about 60% females. In winter he found no males, with a few showing up by spring.
Barnett also set an array of 74 VR2 acoustic receivers 800 metres apart, during the period December 2007 to June 2009. He set them along the boundary of the protected area and at entrances to bays and inlets. For the movement study he tagged 43 animals (31 female) with acoustic tags that communicate with the receivers. The process to implant the tag is a three minute surgery. He found that no Norfolk Bay shark moved to the upper Derwent estuary, and no estuary shark moved to Norfolk Bay. This suggests strong site fidelity. There is some overlap between the populations in late autumn, and by winter most of the sharks (including all the males) left the area. After winter the animals returned to where they were tagged.
Pop up archival tags attached to five males and five females located the makes 1000 kilometres north in Jervis Bay, south of Sydney, and the females closer – slightly offshore, with one visiting a depth of 300 metres. The sharks are more active and in shallower water at night, spreading out more. During the day they spend a lot of time close to the seabed, moving up and down in the water column at night.
Barnett tagged several of the sevengill sharks’ prey species, and determined that the sevengills were only in the bay when their prey items could be found there. The fact that the sharks are not breeding in the area suggests that their habitat use is indeed diet related.
False Bay study (ongoing)
Excitingly, broadnose sevengill cowsharks are the subject of a current study in False Bay involving Dr Barnett and local scientists, making use of the array of acoustic receivers that was originally set to study white shark residency patterns. There are also compatible receivers in Algoa Bay, Mossel Bay, Gansbaai, Port Alfred, Port St Johns and on Aliwal Shoal. At least nine sharks have already been fitted with acoustic tags at Miller’s Point, and a hook was incidentally removed from one shark’s mouth.
Miller’s Point is a unique aggregation site: the researchers aim to determine why. Female sharks that look very pregnant are often observed by divers there. The researchers will use the data from the acoustic receivers to try to determine the sharks’ habitat use in False Bay, their seasonal movements, the population structure and the effects of fishing. This will assisst in managing the species. They will also study their interaction with white sharks (with whom they compete for food), and the cowsharks’ predator-prey interactions with other species. This is important for ecosystem management.
Sevengill sharks have been seen and caught at Robben Island in Table Bay, in Betty’s Bay, and in Gordon’s Bay (at night). It is possible to dive with the Betty’s Bay sharks, if you know where they are! It isn’t known whether there are any at Seal Island, perhaps closely sharing that habitat with the white sharks.
Dr Barnett’s results from his work in Tasmania are fascinating because they shed light on broadnose sevengill cowsharks as a species as well as their specific behaviour in the Derwent estuary. So little is known about our local population that the temptation to try to generalise some ideas from his Tasmanian research is irresistible. I hope that the tagging study currently taking place will increase our understanding of these local celebrity sharks, and that it will assist in managing the species and the places they live so as to ensure that the population continues to thrive. Yay science!
Christopher Neff studies the complex interplay of politics and shark bites on humans. We have heard him speak at the Save Our Seas Foundation, and another article he wrote – that argues that the words we use to describe shark bites or attacks on humans are important – has also featured here.
In January of this year Neff wrote for The Conversation, describing the Western Australian government’s response to a spate of shark fatalities and bites that has left politicians flailing about trying to come up with solutions that made them feel effective. Unfortunately their suggestions – shark hunts and culls – have no scientific basis whatsoever.
On Sunday, the policy [pre-emptive hunting of dangerous white sharks*] was in action when an imminent threat to beach-goers was declared and a catch and kill order was issued for dangerous great white sharks.
However, so imminent was the threat that they could not find any great white sharks for two days. So imminent was the hostility from the white sharks, that they ignored two lines set with bait. All the while, the public was out of the water, alerted to the potential risks and the beaches were closed.
Neff argues that real shark bite prevention involves public education and an acknowledgement of the risks involved in entering the water (with a distinction for different types of watersports, spear fishing being the most dangerous). He mentions recent South African research indicating that water temperature, for example, is a good indicator of the likelihood of spotting a white shark. Thomas Peschak has some suggestions for shark safety in his book South Africa’s Great White Shark. Cape Town’s Shark Spotter program encourages swimmers and surfers to leave the water when a shark is in the vicinity, rather than attempting to remove the possibility of any sharks passing by at all (a fool’s errand).
Politicians drive BMWs (some of them), determine public policy, enact laws and allocate funds (jobs that scientists don’t want to do), but ideally their decisions should be based on evidence and science. This is something that we should constantly strive for.
I’ve been a bit slow off the mark on this one – the paper was published in late January of this year – but here you go: some exciting new research on the white sharks of False Bay has been completed. The study was a long term one (sharks were tracked over a nearly three year period using acoustic tags and receivers situated throughout False Bay) and reveals that female white sharks in False Bay tend to stick around – at Seal Island in winter, and inshore around the beaches in summer – meaning that the area is a critical one for conservation of these animals.
Here is a synopsis of the paper, courtesy of one of its authors, Shark Spotters research manager Alison Kock. Emphasis mine:
Female great white sharks show high residency to inshore coastal area
Seal colonies are well established white shark aggregation areas, but a new study shows that inshore coastal areas (not associated with seals) can be equally as important for white sharks and that use of aggregation areas can differ between the sexes, which has important management implications.
The researchers described their findings in a paper published online January 28 in PLOS ONE (http://dx.plos.org/10.1371/journal.pone.0055048). The study was conducted in False Bay, South Africa where the scientists tracked 56 tagged white sharks of both sexes ranging in size from 1.7 to 5 meters over a period of 32 months.
“We found that white sharks showed high levels of residency to the seal colony over autumn and winter as expected, but we were very surprised to learn that female sharks showed equally high residency at inshore areas during spring and summer and that males were notably absent,” said Alison Kock, who led the study as part of her PhD research at the University of Cape Town (UCT). Kock explains that “the shift from the island in autumn and winter to the inshore region in spring and summer by female sharks mirrors the seasonal peaks in prey abundance including juvenile seals at the island in winter and a range of migratory fish along the inshore during the warmer months”.
White sharks are threatened apex predators and despite South Africa enacting protective legislation in 1991, there is limited knowledge available on how best to make such protection effective. Currently no critical area conservation plans exist for False Bay, or anywhere in South Africa. This study confirms False Bay as a critical area for white shark conservation and identifies that females are particularly at risk, due to their frequent use of the inshore areas of the Bay, which are impacted by fishing, pollution, and damage to natural habitat from coastal development.
Furthermore, the finding that female sharks frequent the inshore regions during spring and summer when recreational use peaks highlights the need for ongoing shark-human conflict mitigation strategies such as the Shark Spotter program in Cape Town, for which Kock serves as the research manager. The Shark Spotters aim to improve public safety while simultaneously conserving this vulnerable shark population.
Although the study focused locally, its findings have broad conservation and management implications because it highlights the need for understanding how behavioural patterns differ between sexes of the same population as this can influence a particular sex’s susceptibility to threats. Co-author, Justin O’Riain, Associate Professor of behavioural ecology at UCT welcomed the findings as an important contribution to the broad field of predator spatial ecology, “We have a wealth of such information for land predators and these results provide an important step in narrowing the knowledge gap between marine and terrestrial systems and assessing the extent of our generalities”.
The paper is available on PLOS ONE, an online journal which is both peer reviewed and international, as well as being open access. Those last two words are golden ones for peasants like me who don’t have access to journal articles that live behind paywalls. Open access journals make scientific results and studies freely available to everyone, including non-scientists. The pie is made higher and everyone benefits from the knowledge and insights that have been obtained. This is a wonderful thing. More scientists should publish like this.
An article on Wired.com led me to this striking composite image created from measurements taken by NASA’s Aura satellite. The satellite measured the amount of nitrogen dioxide (NO2), which is a pollutant created by various forms of human industry (that’s why the coastal areas are so dark) and by ships’ engines. You can see a distinct line between Singapore and Sri Lanka, site of a major shipping lane. There’s more from NASA on the subject here.
Nitrogen dioxide pollution (darker is worse)
Ships’ tracks are also visible at an atmospheric level, as particles from their exhausts float up into the atmosphere and create what looks like the contrails that form behind aeroplanes. There is an explanation of the process, and an image of those kinds of tracks, here (image reproduced below).
Ship tracks visible in the atmosphere
The image of these trails is actually a stereo one and if you have a pair of 3D glasses… they won’t help at all!
It’s quite sobering. Our fingerprints are all over this planet.
Newsweek recently published two articles on the exploration of the ocean.
The first concerns Sylvia Earle and Robert Ballard, both pioneers of ocean exploration. Ballard favours unmanned Remotely Operated Vehicles (ROVs) allowing so-called “telepresence” in the deep ocean by humans, while Earle favours putting actual humans in the ocean as opposed to robots. Aside from the deeper issues it raises, it’s an excellent potted biography of both these eminent ocean explorers, as well as an introduction to the mechanisms available to us when plumbing the sea’s greatest depths.
Ballard’s thoughts on the subject of exploration – and the trajectory of funding – are explained like this:
“The body is a pain,” says Robert Ballard, the marine geologist who discovered the Titanic, striking a common note about the problems with manned travel. “It has to go to the bathroom. It has to be comfortable. But the spirit is indestructible. It can move at the speed of light.”
For two decades, he’s been arguing the virtues of “telepresence” technology: remotely controlled subs and rovers, pumping video to an unlimited number of researchers worldwide. This year he seems to have finally closed the conversation. While the National Atmospheric and Oceanic Administration (NOAA) pulled money from manned exploration, Ballard’s telepresence efforts comprise “the only federal program dedicated to systematic exploration of the planet’s largely unknown ocean,” according to NOAA’s Office of Ocean Exploration and Research.
The second article is a response by directorJames Cameron to Robert Ballard’s assertion that unmanned submersibles are the future of ocean exploration. Cameron visited Challenger Deep in the Mariana Trench, nearly 11 kilometres deep, in March 2012. His view is that
No kid ever dreamed of growing up to be a robot. But they do dream of being explorers. And inspiring young minds and imaginations is one of the most important things we can be doing if we want a future supply of engineers and scientists insuring our lead in innovation.
Andrew Thaler of Southern Fried Science (the best ocean-related blog I read) wrote an eloquent summation and response to both these articles. His assertion is that there is actually very little distinction between manned and unmanned ocean exploration, particularly at the extreme depths that the Deepsea Challenge expedition operated at (and at depths much less than that, too). Cameron did not look out of a viewport or window in his submersible; he viewed the output of an array of 3D cameras, on a screen, from inside the sub. Thaler makes his point convincingly:
Technology doesn’t create explorers, explorers create technology. Any tool, from Wormcam to Alvin, that provides a glimpse into the wonderful unknown, is a tool worth having.
It is the ocean that inspires us. Everything else is hardware.
His point is that to get caught up in what is very nearly a purely semantic discussion over which form of exploration has greater virtue and potential is to miss the point that funding is lacking and political will to explore the ocean is low. Perhaps one day, when we’re knee deep in ROVs and manned submersibles, we can have this discussion again. For now – anything that assists people to see what’s under the sea is a good thing.
The Humboldt (or jumbo) squid is a giant (can be over 1.5 metres long), extremely intelligent, ruthless predator that will not hesitate to engage in cannibalistic behaviour. They are named after the Humboldt Current that flows along the west coast of South America. They exist in huge numbers, can swim at up to 24 kilometres per hour – which is very fast in the water – and move about in large shoals. Their skin colour can change rapidly from white to red and back again, and while they prefer deep (over 200 metres) water, they are found in shallower waters too, particularly at night.
Tim Zimmermann wrote an article for Outside about the slightly lunatic (but awesome) sounding Scott Cassell and his work photographing and diving with Humboldt squid in the Sea of Cortez. Cassell is a number of things – counterterrorist specialist, professional trapeze artist, and experienced diver. He has done some cool stuff and is a character well worth reading about.
Humboldt squid have been aggressive (or boisterous, if you don’t want to anthropomorphise) towards divers, so various precautions are taken when getting in the water with them. Among these are safety lines clipped to the boat so that divers cannot be dragged deeper by a squid pile-on, and the use of fibreglass body armour to protect against the clinging tentacles of the squid. It sounds absolutely thrilling.
Outside magazine published a wonderful article by Tim Zimmermann in September 2012, describing the research of Denise Herzing (of the Wild Dolphin Project) into a specific pod of Atlantic spotted dolphin in the Bahamas. Among her research interests are attempting to establish communication between dolphins and humans, by synthesising the clicking sounds that these animals use to communicate. In order to do this, the researchers are first working to identify patterns of sound used by the dolphins, with the aim of decoding the patterns and “translating” their speech.
It’s an ambitious, exciting experiment. I think it appeals to me because nowhere is there any hint of wild-eyed bushy-haired fanaticism, or a secretly held dream that the dolphins “have so much to share with us” or whispers that they are expected to be purveyors of interplanetary wisdom. Dolphins are highly intelligent creatures, but they also spend an inordinate amount of time trying to have sex with one another (I can’t decide whether this confirms their intelligence, or happens in spite of it). The scientists do not seem (from this brief article) to be harbouring any expectations of enjoying particular avenues of discussion with the dolphins. This is important for good science, and in stark contrast to the musicians described in Thousand Mile Song, who are bent on imposing their musicality on whales but exhibit little respect for the very creatures they try to engage.
The article is a dreamy read that makes me want to run away and become a dolphin scientist (much as Dolphin Confidential did). Read the full piece here.
Researchers at the National Marine Mammal Foundation have released a paper on whale vocalisations, and Phys.org reports on it. In the mid-1980s a beluga was recorded making noises that imitated human speech to the extent that a diver in his tank thought that someone was calling to him from above the water.
I don’t understand why it took nearly 30 years to publish this paper, concerning a long-dead whale, but one can’t know everything. I also wonder in passing whether we (humans) are not imposing our formidable pattern-recognition abilities on random sounds from the whale.
It is a bit sad that we even know that beluga are capable of the vocal contortions required to imitate human speech (actually quite difficult for them). I am bothered that a comment by one of the researchers – “Such obvious effort suggests motivation for contact” – could be used by advocates of keeping beluga captive to argue that the creatures enjoy captivity, rather than the situation forcing them to seek entertainment by whatever meagre means are at their disposal.
I am a beeeeg fan of citizen science. This is what happens when non-professional scientists, such as you and I, gather scientific data or do experiments that can lead to real scientific results. This is immensely satisfying, specially for someone like me who is probably in the wrong (non-scientific) career, but (for various reasons) isn’t going to change it any time soon.
When I was at university, my friends and I participated in the SETI@home project, donating our computers’ spare processing cycles to analysing radio telescope data in search of aliens (and other interesting data). In this way the researchers were able to analyse far more data than if they’d just used the computing power at their personal disposal. These days, Tony and I participate in western leopard toad research by submitting photos of our resident toad (Franklin) to iSpot.
With modern sampling methods, silly amounts of data can be generated – more than a single scientist or team could process in several lifetimes. Enlisting the help of the man on the street to filter the data down to what is interesting saves time, and enables studies of impressive magnitude to be undertaken.
Seafloor Explorer
The Seafloor Explorer project allows the general public to analyse images taken by HabCam, a camera that flies above the ocean floor (towed by a ship) taking six images per second. The camera is completely non-invasive, and the latest version actually comprises two cameras in stereo, which allows size measurements to be taken, as well as some other sensors. Participants in the project will look through photos from the camera, and identify the material of the ocean floor (for example, sand or gravel) and what organisms they can see in each frame. The interface also allows measurements to be taken.
One way in which this system can be (and is being) used is for fisheries management of benthic species such as scallops. This enables better quotas to be set. One could also assess habitat damage from trawling activities. The interface is simple, and interesting images can be shared on Twitter and facebook if participants desire to do so.
