South Carolina Bull Shark

Another shark video is making the viral rounds on the Internet. But rather than be one that invokes sadness or anger for depicting some poor trophy prize hung by its tail or a sea of shark fins drying in the sun, this short video from South Carolina illustrates a unique quality of what is considered to be one of the more aggressive sharks. Along South Carolina's North Myrtle Beach is House Creek which is fed by tens of smaller creeks and streams and ultimately spills out to the sea. This transition from fresh to saltwater makes for brackish water that some ocean fish are able to tolerate. One such animal is the bull shark. If you have not yet seen the video, a young woman, Sarah Brame, accompanied by her fiance and stepfather, was fishing off the dock at Cherry Grove Inlet, a small body of water connected to House Creek by a small feeder stream. As she was reeling in her first fish, a local variety called drum, a 5-6 foot bull shark suddenly lunged, breaking the surface and taking her catch in one swift flurry of splashing water and hungry shark. Quite a remarkable piece of video (see below).  What makes the video all the more remarkable is its illustration of the bull shark's ability to withstand brackish to near fresh water, which allows it to move up streams and rivers and get into places where you least expect to find a large shark. (See the map of the Cherry Grove Inlet and House Creek.) Bull sharks have been found many miles upstream in South American rivers and the famous Matawan Creek shark attack of 1916 in New Jersey, which many at the time attributed to a great white, was, in hindsight,
 very likely  a bull shark. Bull sharks are also one of the more aggressive sharks. Aggressive in that, when on the hunt, they do not rely on a single massive bite, like a white shark will do to a seal (or a mistaken swimmer). Instead, the bull shark will hunt large prey with repeated bites. This has been borne out by reports of swimmers or surfers who, when attacked by a bull shark, found that it would give chase and bite repeatedly in a rather tenacious, never-give-up manner. While a bull shark, like all sharks, do not single out humans as a specific prey, it is this determined behavior by the bull shark that puts it in the top four of most dangerous sharks (the other three being, white sharks, tiger sharks, and oceanic white tips). I have had the opportunity to get up close with a variety of shark species and the bull shark is the one that draws my utmost attention. After Sarah lost her catch in such a spectacular fashion, her fiance and stepfather contemplated taking their 10-foot boat out on the water to track down the shark, but after a few minutes on the water, they rethought the matter. "We need a bigger boat and a bigger net," said Van Hughes, Sarah's stepfather. "We need a bigger boat." Now, where have I heard that before. . . .  According to Dan Abel, shark researcher at the Coastal Carolina University, "It's not like just because we saw this shark yesterday that was just chasing this fish that was struggling on a line means that everything is going haywire. They're out there all the time anyway. It just so happens that this one opportunity a person caught it on film." Just another apex predator doing its thing.Source: RTSea Blog

Read More........→July 21, 2012

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