South Africa’s great white sharks are changing locations – they need to be monitored for beach safety and conservation

South Africa is renowned for having one of the world’s biggest populations of great white sharks (Carcharodon carcharias). Substantial declines have been observed, however, in places where the sharks normally gather on the coast of the Western Cape province. Sharks congregate at these locations to feed, interact socially, or rest.

In Cape Town, skilled “shark spotters” documented a peak of over 300 great white shark sightings across eight beaches in 2011, but have recorded no sightings since 2019. These declines have sparked concerns about the overall conservation status of the species.

Conserving great white sharks is vital because they have a pivotal role in marine ecosystems. As top predators, they help maintain the health and balance of marine food webs. Their presence influences the behaviour of other marine animals, affecting the entire ecosystem’s structure and stability.

Marine biologists like us needed to know whether the decline in shark numbers in the Western Cape indicated changes in the whole South African population or whether the sharks had moved to a different location.

To investigate this problem, we undertook an extensive study using data collected by scientists, tour operators and shore anglers. We examined the trends over time in abundance and shifts in distribution across the sharks’ South African range.

Our investigation revealed significant differences in the abundance at primary gathering sites. There were declines at some locations; others showed increases or stability. Overall, there appears to be a stable trend. This suggests that white shark numbers have remained constant since they were given protection in 1991.

Looking at the potential change in the distribution of sharks between locations, we discovered a shift in human-shark interactions from the Western Cape to the Eastern Cape. More research is required to be sure whether the sharks that vanished from the Western Cape are the same sharks documented along the Eastern Cape.

The stable population of white sharks is reassuring, but the distribution shift introduces its own challenges, such as the risk posed by fisheries, and the need for beach management. So there is a need for better monitoring of where the sharks are.

Factors influencing shark movements

We recorded the biggest changes between 2015 and 2020. For example, at Seal Island, False Bay (Western Cape), shark sightings declined from 2.5 sightings per hour in 2005 to 0.6 in 2017. Shifting eastward to Algoa Bay, in 2013, shore anglers caught only six individual sharks. By 2019, this figure had risen to 59.

The changes at each site are complex, however. Understanding the patterns remains challenging.

These predators can live for more than 70 years. Each life stage comes with distinct behaviours: juveniles, especially males, tend to stay close to the coastline, while sub-adults and adults, particularly females, venture offshore.

Environmental factors like water temperature, lunar phase, season and food availability further influence their movement patterns.

Changes in the climate and ocean over extended periods might also come into play.

As adaptable predators, they target a wide range of prey and thrive in a broad range of temperatures, with a preference for 14–24°C. Their migratory nature allows them to seek optimal conditions when faced with unfavourable environments.

Predation of sharks by killer whales

The movement complexity deepens with the involvement of specialist killer whales with a taste for shark livers. Recently, these apex predators have been observed preying on white, sevengill and bronze whaler sharks.

Cases were first documented in 2015 along the South African coast, coinciding with significant behavioural shifts in white sharks within Gansbaai and False Bay.

Although a direct cause-and-effect link is not firmly established, observations and tracking data support the notion of a distinct flight response among white sharks following confirmed predation incidents.

More recently, it was clear that in Mossel Bay, when a killer whale pod killed at least three white sharks, the remaining sharks were prompted to leave the area.

Survival and conservation of sharks

The risk landscape for white sharks is complex. A study published in 2022 showed a notable overlap of white sharks with longline and gillnet fisheries, extending across 25% of South Africa’s Exclusive Economic Zone. The sharks spent 15% of their time exposed to these fisheries.

The highest white shark catches were reported in KwaZulu-Natal, averaging around 32 per year. This emphasised the need to combine shark movement with reliable catch records to assess risks to shark populations.

As shark movement patterns shift eastward, the potential change in risk must be considered. Increased overlap between white sharks, shark nets, drumlines (baited hooks) and gillnets might increase the likelihood of captures.

Beach safety and management adaptation

Although shark bites remain a low risk, changing shark movements could also influence beach safety. The presence of sharks can influence human activities, particularly in popular swimming and water sports areas. Adjusting existing shark management strategies might be necessary as distributions change.

Increased signage, temporary beach closures, or improved education about shark behaviour might be needed.

In Cape Town, for example, shark spotters have adjusted their efforts on specific beaches. Following two fatal shark incidents in 2022, their programme expanded to Plettenberg Bay. Anecdotal evidence highlights additional Eastern Cape locations where surfers and divers encounter more white sharks than before.

Enhanced monitoring and long-term programmes

Further research is required to understand the factors behind the movements of sharks and their impact on distribution over space and time. Our study underscores the importance of standardising data collection methods to generate reliable abundance statistics across their entire range. Other countries suffer from the same problem.

Additionally, we propose establishing long-term monitoring programmes along the Eastern Cape and continuing work to reduce the number of shark deaths.

Sarah Waries, a master’s student and CEO of Shark Spotters in Cape Town, contributed to this article.

Alison Kock, Marine Biologist, South African National Parks (SANParks); Honorary Research Associate, South African Institute for Aquatic Biodiversity (SAIAB), South African Institute for Aquatic Biodiversity; Alison Towner, Marine biologist, Rhodes University; Heather Bowlby, Research Lead, Fisheries and Oceans Canada; Matt Dicken, Adjunct Professor of Marine Biology, Nelson Mandela University, and Toby Rogers, PhD Candidate, University of Cape Town

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Read More........→September 21, 2023

Sharks may show the way for humans to re-grow teeth

Sharks can regenerate their teeth through the network of genes, which may pave the way for the development of therapies to help humans with tooth loss, say researchers.

Although humans possess same cells, their tooth regeneration ability is limited. But the study has identified a network of genes that enables sharks to develop and regenerate their teeth throughout their lifetime.

''We know that sharks are fearsome predators and one of the main reasons they are so successful at hunting prey is because of their rows of backward pointing, razor-sharp teeth that regenerate rapidly throughout their lifetime, and so are replaced before decay,'' said lead author Gareth Fraser from the University of Sheffield in Britain.

Researchers have identified how a special set of epithelial cells form, called the dental lamina, which are responsible for the lifelong continuation of tooth development and regeneration in sharks.

The genes also allow sharks to replace rows of their teeth using a conveyer belt-like system.

Humans also possess this set of cells, which facilitate the production of replacement teeth, but only two sets are formed – baby and adult teeth – before this set of specialised cells is lost.

These ''tooth'' genes therefore make all vertebrate teeth from sharks to mammals. However in mammals like humans, the tooth regeneration ability, that utilises these genes, has been highly reduced over time.

''The Jaws films taught us that it's not always safe to go into the water, but this study shows that perhaps we need to in order to develop therapies that might help humans with tooth loss,'' Fraser said.

Through analysing the teeth of catshark embryos, the researchers characterised the expression of genes during stages of early shark tooth formation.

They found that these genes participate in the initial emergence of shark's teeth and are re-deployed for further tooth regeneration.

The study suggests that at the beginning of the sharks' evolutionary history, their teeth were most likely continuously regenerated and used a core set of genes from members of key developmental signalling pathways, which were instrumental in sharks evolving to maintain the ability to re-deploy the genes to replace teeth when needed. Source: http://www.domain-b.com/

Read More........→November 16, 2016

Shark Net: Dr. Barbara Block/TOPP release great app to track California's white sharks

I have been fortunate to meet and speak with many accomplished marine scientists and researchers. One who is definitely on my Top 10 list is Dr. Barbara Block. Based at Stanford University, California, she oversees TOPP (Tagging of Pacific Predators), a program started in 2000 that tracks pelagic animals from tuna to swordfish to turtles to great white sharks, and more. (Couple of previous posts on the subject here & here.) Barbara is a spunky taskmaster but, working with her staff, it is that very drive  that  has  enabled
TOPP to discover many of the secrets involving the migration patterns of these large and critically important animals.  It was TOPP that coined the phrase "White Shark Cafe" to describe where great white sharks from California and Mexico migrate to in the Pacific Ocean. One particularly important finding regarding these migration patterns was the possible explanation for the seasonal nature of the sharks' sojourns: Mid-Pacific upwellings which bring nutrients that feed the food chain and ultimately replenish the larger fish that the sharks feed on. Cyclical weather and ocean movement patterns produce these upwellings - and as climate change continues to present itself, there is always the possibility of shifts in the upwelling cycle that could have unknown consequences for these animals. Whenever I am called upon to speak about sharks, these fascinating migration patterns are always a topic I include as I am guaranteed they will mesmerize my audience. So, thank you, Dr. Block! While Internet users can monitor the ongoing activities of TOPP through its website, it's now possible to carry it with you on your iPhone or iPad. Shark Net - Predators of the Blue Serengeti is available fromiTunes at no charge (as in free!) and provides a range of features on the cataloging and whereabouts of those most iconic of California ocean predators, the great white shark. Users can get updates on the latest monitoring of sharks, pinpoint the location of the tracking buoys that gather the data, and get biographies, photos, and videos about many of the sharks that frequent California's waters. There are other apps available that provide white shark tracking info but this is thedefinitive app for monitoring the white sharks that ply the waters off California's coast - and beyond, thanks to those incredible migration patterns. In a recent interview for U.K.'s The Guardian, Dr. Block explained her use of the term "Blue Serengeti" to describe California's coastal waters and the large migration patterns that occur within it. "White sharks and tuna travel for thousands of miles before returning to the same hot spot just as salmon do when they return to the same stream. These journeys are the marine equivalent of wildebeest migrations that take place on the Serengeti plain in Africa. That is why I call this part of the Californian coast the Blue Serengeti." "Everyone knows about watering holes on the Serengeti even though most of us have never been there. We can just close our eyes and see the zebras, the elephants and the hyenas. We want to do the same for the migration hot spots we have found off the coast of California." Dr. Block and TOPP are setting new standards for ocean animal tracking, expanding on the various GPS and satellite tracking methods (which can sometimes provide data intermittently) to include cutting-edge, round-the-clock monitoring technology using monitoring networks or even self-contained, solar-powered tracking stations like Wave Glider that travels the currents along the California coast.  Through the efforts of TOPP and consumer apps like Shark Net, Dr. Block hopes to bring the hidden complexity of our ocean planet to a wider audience. Humankind's curiosity makes it look outward, and that has lead us into the stars. But there is a whole world to be discovered starting right at the shoreline. "Human technology has made it to Mars. We are transmitting gorgeous pictures from it. Yet we have not explored our own planet. Two-thirds of it is covered with oceans that are still mysterious places. We are trying to hook people up to what is going on out there now and get them to realize that it could all be lost if we did not do something to protect it. Ultimately, I want to create a world heritage site here. Wiring up the oceans, as we are doing, is our way to get people to understand the importance of these places."Source: RTSea

Read More........→February 08, 2013

Here Are The Most Vicious Fish Of All Time

Credit: George Washington University

The black piranha and the extinct giant piranha, or megapiranha, have the most powerful bites of carnivorous fishes, living or extinct, once body size is taken into account, finds researchers in a paper recently published in Scientific Reports. The research paper, Mega-Bites: Extreme jaw forces of living and extinct piranhas, highlights the piranhas’ specialized jaw morphology, which allows them to attack and bite chunks out of much larger prey. Guillermo Ortí, the George Washington University Louis Weintraub Professor of Biology in the Columbian College of Arts and Sciences, is one of the authors of the paper. His research focuses on the evolution of fishes in general, but specializes on Amazonian fishes, to unravel evolutionary relationships based on DNA sequence data. In 2010, Dr. Orti along with other researchers participated in an expedition to the Xingu and Iriri rivers in Amazonia to collect the data on the fish. Comparison of anterior bite forces among apex fish predators using calculated Bite Force Quotients (BFQ). BFQ's correct for absolute differences in bite forces attributable to drastic differences in body size by comparing mass specific residuals. Species with generally average bite strengths for their body size have a BFQ of 100. Black and white bars represent the lowest and highest quotients from small and large

Credit: © Gray Taxidermy.Dunkleosteus terrelii image © Karen Carr. Nature

body size estimates, respectively. Barracuda and shark images Piranhas’ aggressive nature, relatively small size and accessible populations make them a suitable group of predatory vertebrates in which to study the evolution of extreme biting capabilities. Even at their small body sizes, diet studies indicate that piranhas will attack and bite chunks of bony fins and flesh from prey many times larger than themselves. Guillermo Ortí, the George Washington University Louis Weintraub Professor of Biology, posing with piranhas during a trip to the Amazon In spite of their reputation, no quantitative data or empirical estimates regarding the piranhas biting abilities were available. The paper reports the first bite-force measurements taken from wild specimens of the largest species of carnivorous piranha in the
Amazon, the black piranha, and describes the underlying functional morphology of the jaws that allows this creature to bite with a force more than 30 times greater than its weight. The powerful bite is achieved primarily due to the large muscle mass of the black piranha’s jaw and the efficient transmission of its large contractile forces through a highly modified jaw-closing lever. The expedition was organized and filmed by National Geographic. A subsequent program called Megapiranha aired on the National Geographic Channel featured the expedition and focused on the creature that existed millions of years ago. “It was very exciting to participate in this project, travel one more time to the Amazon to be able to directly measure bite forces in the wild,” said Dr. Orti. “I learned a lot of biomechanics from my colleagues while collecting valuable specimens for my own research.” The authors also reconstructed the bite force of the megapiranha, showing that for its relatively diminutive body size, the bite of this fossil piranha dwarfed that of other extinct mega-predators, including the whale-eating shark and the Devonian placoderm. Research at the Ortí lab at GW continues to focus on reconstructing the genealogical tree of fishes including piranhas based on genomic data. Scientific Reports is a primary research publication from the publishers of Nature, covering all areas of the natural sciences. Contacts and sources: Rice Hall, George Washington University, Source: Nano Patents And Innovations

Read More........→December 23, 2012

Sharks Are Color Blind: new study shows they live in a world of contrast

According to a new study by scientists from Australia, sharks are color blind. This puts them in the same category as whales and dolphins as sea creatures that may have had color vision at one time but evolved to a black and white world, perhaps as a more effective means of hunting. Previous studies of several species of rays, part of the same general family as sharks, were found to have several types of ospins or light sensitive proteins in the photoreceptors of their retinas which provide them with the ability to see in color. But studies of wobbegong sharks showed them to not have the necessary levels of ospins for color, only black and white. Dr. Susan Theiss, University of Queensland (yes, we're related - she is my niece), and her colleagues studied two different species of wobbegong sharks; each of which prefer different levels of depth in the sea as their normal habitat. Because of those differences in depth, the vision of the two species is more sensitive to different wavelengths of light. Each species is better attuned to the type of light that predominantly penetrates their environment. One wobbegong shark species preferred deeper water where it is penetrated by shorter wavelengths - a bluish kind of light. Sharks in shallower water can be more sensitive to red or green spectrums of light. Color blind as they are then, sharks live in a world of contrast. Their other senses of sound and scent can aid them in their search for prey then, at some point, contrasting visual stimuli kicks in, and at close range sensing electrical impulses can come into play. Sometimes color can be a distraction and can prevent the shark from staying focused on a potential target. Color exists in nature for a variety of reasons and in some environments it can actually act as a kind of camouflage. Oddly enough, as a filmmaker, I typically use a black and white viewfinder with my camera as it can often provide a sharper image for focusing purposes. Playing off that sense of visual contrast, it might be possible to help keep sharks from becoming accidental bycatch by camouflaging or making hooks less visually interesting. And the same could possibly be said for surfers who provide considerable contrast (as does a seal) in their black wetsuits. "If we can use this knowledge to design longline fishing lures that are less visible to sharks then we will be able to reduce the amount of shark bycatch. We may also be able to make wetsuits less attractive, and make the water safer for surfers and divers," says co-author Associate professor Nathan Hart of the University of Western Australia and reported in Australia's ABC Science.Source: RTSea

Read More........→October 21, 2012