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Creature Feature: Great Hammerhead Shark

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In this series, the Shark Trust will be sharing amazing facts about different species of sharks and what you can do to help protect them.

We’re kicking off the new year with a classic shark – the Great Hammerhead. Known for their distinct silhouette, the Great Hammerhead is the largest species of hammerhead on the planet.    

With a distinct notch on the centre of their head, the Great Hammerhead is light grey or brown above and white below. Reaching a maximum size of around six metres, this is a big shark. There are nine species of hammerhead. Identifying them often relies on looking at head shape. The Great Hammerhead has a much straighter front edge compared to the Scalloped and Smooth Hammerheads. 

The unique hammer-shaped head (a.k.a. cephlafoil) improves their manoeuvrability. As the position of their eyes enable them to see 360°. And enhances their ability to detect electrical currents, a sixth sense that all sharks have. Sharks have lots of tiny pores covering their head and snout, called ampullae of Lorenzini. These are extremely sensitive and can detect even the faintest of electrical fields. Including those generated by the Earth’s geomagnetic field, or muscle contractions in prey. The broad flat head of a hammerhead provides a much larger surface area for these pores. Which is why they’re so good at finding prey – such as stingrays – completely buried beneath the sand. 

Great Hammerheads are nomadic and seasonally migratory. They move towards the equator during the winter and then towards the poles during the summer. Unlike other species, they are solitary and migrate up to 1,200km (750 miles) alone.

The Great Hammerhead is Critically EndangeredPopulations have declined in recent years. They are targeted and also caught as bycatch.

Although large and powerful, research has shown that Great Hammerheads are quite fragile. They are particularly vulnerable to the stress of capture. Recent research has found that individuals that are hooked have a 50% chance of dying following release. Combating the declining populations comes down to, as always, implementing scientifically informed catch limits and enforcing these. 

The species is important for dive tourism in some areas. In the video below, head of marketing for the Shark Trust – Caroline, takes in the view as a Great Hammerheads cruise by. They are a true sight to behold.

SCIENTIFIC NAME:  Sphyrna mokarran

FAMILY:  Sphyrnidae

MAXIMUM SIZE:  610cm 

DIET:  Varied. Preference for stingrays, other rays and marine catfish.

DISTRIBUTION: Worldwide, tropical seas. 

HABITAT:  Coastal-pelagic and semi-oceanic. Close inshore to well offshore. 1-300m or more.

CONSERVATION STATUS: Critically Endangered


Images from Frogfish Photography 

Distribution Map from Wikimedia Commons 


For more amazing facts about sharks and what you can do to help the Shark Trust protect them visit the Shark Trust website by clicking here.

The Shark Trust is the leading UK-based shark conservation charity. The team works globally to safeguard the future of sharks, and their close cousins, the skates and rays. Engaging with a global network of scientists, policymakers, conservation professionals, businesses and supporters, to further shark conservation. Established in 1997 to provide a voice for UK sharks, the Shark Trust has an ever-growing number of passionate supporters. And together we're creating positive change for sharks around the world. Want to join us and help protect sharks around the world? Click here! www.sharktrust.org

Marine Life & Conservation Blogs

Dragons of the sea

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Guest Blog by Staci-lee Sherwood

The most fascinating and unique characteristic of the Syngnathidae family is how it’s the male that gives birth.  This fish family includes Seahorses,  Pipefish and Seadragon.  Having a head like a horse, Seahorses and Seadragons stand out as a fish species in the marine world.  They are true rock stars of the ocean and a favorite among photographers.  Their tiny size and elusiveness just add to their appeal.

Seadragons

Lesser known than their more famous cousins they are stars in their own right.  These tiny dragons of the sea are larger in size with more color and intriguing patterns.  Found only in southern Australian waters makes them rare.  There are three recognized species, the Weedy, Leafy and newly described Ruby seadragon.

Elusive species are more alluring to scientists because of the chance to be the first to discover something new.  Not much is known about their lives and researchers hope to shed light on these rainbow colored fish.  Their diet consists of tiny mysid shrimp and other zooplankton.  After mating the female deposits up to 300 eggs into the male’s brood patch who then fertilizes and carries them till birth.  Despite their being much larger than Seahorses, which range in size from 1 – 6 inches, they produce  about 1/3 of the eggs. Seadragons range in size from 13 – 18 inches

weedy seadragon: John Turnbull

In 2006 the IUCN listed them as Near Threatened on the Red List.  A lot has changed since then.  As the Seahorse population continues to decline China might look more toward the Seadragon to fill the void.

Seahorses

One fascinating fact about this family of fish they lack teeth or stomachs.  Instead they suck up food through their snout.  Lacking a stomach means food goes in and out rather quickly.  Seahorses will mate for life.  During the courtship dance they curl their tails and change color.  Following the mating ritual it’s the female that deposits up to 1,000 eggs in the male’s pouch.  A handy survival skill, like the chameleon, they can change color to blend into their surroundings.

Diminutive in size they capture the imagination of young and old alike but are in serious danger of going extinct.  Illegal harvesting by China for traditional medicine, used as decoration in key chains and pendants and polluted water have taken their toll.  Without global bans on their exploitation and fierce enforcement the world could lose these horse looking fish.  There are over 40 recognized species globally.

Florida

Many Floridians don’t know we have three species of seahorses, the Dwarf, Lined and Long Snouted.  These are all listed as either Vulnerable or Threatened in US waters.  One of the biggest threats in Florida is the heavily polluted water they live in.  Seahorses live in shallow tropical waters where their habitat is coral reefs, seagrass beds and mangroves.  Unfortunately in Florida the water quality is so poor most of the seagrass is dead while the bleaching of coral reefs has caused their decline.  A bleak future awaits this species.

Seahorses mating in the water column at Blue Heron Bridge in Florida, USA 2022

Globally all species are being pulled from the ocean so Florida populations are at risk of extinction.  A  favorite among divers, some local populations have fan clubs where divers will make special trips hoping to see them.

Australia

The White’s Seahorse, also known as the Sydney Seahorse, has a population decline over 90%.  In 2018 they became the second seahorse species in the world to be listed on the IUCN Red List Status as endangered.  Alarmed scientists took this opportunity to try to save them in a unique way.  Research showed this species uses artificial reefs if natural ones are absent.  David Harasti, Senior Research Scientist at Port Stephens Fisheries Institute, created the ‘Seahorse Hotels’ out of metal cages.  Once placed underwater they soon attract a variety of marine life like Coral and Sponges.  In a matter of weeks they’re covered and start attracting endangered Seahorses.

I spoke with Dr. Harasti about the use of these hotels for other species, especially those found in other parts of the world.  Regarding their use Harasti said the use of hotels may only be suitable for particular seahorse species. We know that they work really well for those species that like artificial habitats such as the White’s seahorse and Pot-belly seahorse in Australia and the Short-head seahorse found in Europe.”

Two tagged juvenile White’s Seahorses living in a hotel 4 months after deployment (Photo: D. Harasti)

Captive bred juvenile seahorses are released into hotels hoping they will breed and help recover their population.  Surveys show adult seahorses have also taken to them.  The project has only been around a few years so it’s too early to tell if the population will rebound.  Illegal harvesting worldwide must stop and laws must be enforced.  With such a steep decline of a species that gets little attention we need real conservation on a global scale now.  Click here to learn more about these hotels and watch some amazing videos https://www.dpi.nsw.gov.au/fishing/species-protection/what-current/endangered-species2/whites-seahorse

South Africa

In 2017 a photograph taken off the eastern coast of South Africa in Sodwana Bay  by Savannah Nalu Olivier showed a new species barely the size of a fingernail.  After viewing the photograph, pygmy seahorse expert Richard Smith realized this was a new discovery.  This is the first pygmy seahorse discovered in the Indian Ocean.  Most pygmy seahorses survive by camouflage among vegetation so what an amazing find to see something so microscopic.  To read the 2020 study click here   https://zookeys.pensoft.net/article/50924/

Photo by Richard Smith, via University of Leeds

Global threats

According to Seahorse Trust the biggest threat to survival is the taking of an estimated 150,000,000 every year, mostly by China, to be used in their traditional medicine.  The use of Seahorses for asthma and impotence has no scientific basis and can be fixed with modern medicine.  Another 1,000,000 are caught for captivity in personal aquariums. There are no accurate numbers for how many end up used in trinkets but it’s estimated 1,000,000 are lost.  At this rate we will push this species toward extinction.

In the past twenty years there has been a global increase in the capture and selling for use in about 80 countries.  Varying degrees of threats exist for different species and different regions.  Somewhere between 50 -97% decline in their population makes for an urgent call to end their use whether for personal and medical reasons.  The world must agree to a ban with enforcement or lose one of its most amazing creatures .

Help save our Seahorses and Seadragons with these do’s and don’ts:

  • Don’t buy dried Seahorses, or trinkets that use them
  • Don’t buy live Seahorses for aquariums
  • Do use modern medicine which is effective and safe instead of Traditional Chinese Medicine
  • Never pollute the water
  • Support conservation efforts
  • Spread the message

To learn how to help Seahorses  https://www.theseahorsetrust.org/

To help conservation in Australia https://www.visitsealife.com/sydney/conservation/


Header Image: Tony Brown

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Marine Life & Conservation Blogs

For PADI divers, every week is Shark Week!

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Some of our favorite places to have epic interactions with the stars of Shark Week – dive certification not always required!

We’ve been all around the world diving with sharks from the smallest shy shark to the giant whale shark. Here’s some of the best places in the world to swim, snorkel and dive with the iconic and most popular stars of Shark Week – including Whites, Bulls, Tigers, Great Hammerheads, and Mako Sharks – while shifting your perspective at the same time!

Image Credit: Andy Casagrande @ABC4EXPLORE

Great White Sharks – Guadalupe Island, Mexico

PADI Diving Certification required: None

Other Shark Species You’ll encounter:  None (they don’t want to end up on the White Shark’s menu!)

Want to have the same experience people like PADI Diver Andy Casagrande film for Discovery’s Shark Week? Head to a remote archipelago off the coast of Baja.

Guadalupe Island is off the coast of Mexico and is absolutely epic for experiencing white sharks doing what they do best. This small volcanic island is located 150 miles off the west coast of Mexico and is home to approximately 170 great white sharks from July to November.

The water is crystal clear, topside conditions are usually great – and the action is incredible, and highly reliable. While we are dealing with wild animals that make their own itineraries, it isn’t unusual to see 20 – 30 different animals on a trip!

The island’s shores are havens for Guadalupe Fur Seals, Californian Sea Lions and Northern Elephant Seals. It also brings in incredible amounts of pelagic fish species like tuna. It’s a 24-hour diner filled with white sharks’ favorite food from late July through the end of each year.

Some of the biggest sharks in the world have been tagged in Guadalupe including “Deep Blue”. The action at the surface can be busy with the huge females hunting large elephant seals and from the in-water cages, it’s incredible to witness the social structures and the interaction between sharks.

Many operators serving Guadalupe Island offer the unique experience of liveaboard diving with great whites. While it may not be the easiest place to reach, thanks to the large population of migrating sharks and clarity of the water, this is a great choice for a great white shark encounter.

And you don’t need to be a certified diver! You’ll have surface supplied air and plenty of time in cages built for your – and the sharks’ safety.

Choose from 7 PADI Liveaboards in Guadalupe Island

Other White Shark Hotspots:

Image Credit: Neil Andrea and @juliesharkangel

Tiger Sharks – “Tiger Beach”, Bahamas

PADI Diving Certification required: Open Water Diver or Freediver

Other Shark Species You’ll Encounter:  lemon sharks, reef sharks, nurse sharks and the occasional great hammerhead

Named because of their unique stripes and impressive hunting style, tiger sharks can be found in tropical and sub-tropical regions around the globe. These beautiful marine animals can reach up to 5 meters/16 feet in length and can weigh up to 635 kg/1,400 lb.

Tiger sharks have gotten a bad reputation on Shark Week as being indiscriminate eaters (yes, it’s true a suit of armor and an unexploded grenade have been found in the stomachs of this species) – and dangerous sharks. However, swimming with one – whether snorkeling, freediving or diving is a life-changing experience. You’ll quickly realize that you are having an adventure of a lifetime as the fear melts away. And there is really no place on earth like this place off the coast of the Bahamas – that exists only below the surface.

About an hour by boat from the West End of Grand Bahama, Tiger Beach is famous and aptly named for its resident tiger sharks. Two to seventeen of these gorgeous animals reliably appear nearly every day of the year. Tiger Beach offers the chance to take part in some of the greatest shark diving in the world. You’ll get up-close encounters with not only tiger sharks but lemon sharks, the occasional hammerhead and plenty of whitetip reef sharks in the crystal-clear azure waters that only an aquarium can top in terms of visibility.

The best time to dive Tiger Beach is between October and January when the sharks use the area as a breeding ground. Shark Week has featured some of the residents being tagged or even giving birth – and hopefully you’ll even meet Emma, the world’s most famous Tiger Shark.

From Bimini or Grand Bahamas, you can head to the most spectacular tiger shark gatherings in the world by a day boat – or you can take a trip on a liveaboard departing from Southern Florida or the Bahamas. The easy surface conditions, 20-foot depth and gorgeous light make Tiger Beach accessible for freedivers and scuba divers alike.

View Dive Operators in the Bahamas

Other Tiger Shark Hotspots:

Image Credit: Beqa Adventure Divers

Bull Sharks – Shark Reef, Fiji

PADI Diving Certification required: Advanced Open Water Diver

Other Shark Species You’ll Encounter:  tiger sharks, gray reef sharks, nurse sharks, black tip reef sharks, silvertip sharks

Part of many different Shark Week episodes, bull sharks are well known sharks for many reasons – including a reputation for brutish behavior (which earns them their name) as well as the fact they are one of the most adaptable species of all sharks. They can survive in both salt and fresh water and can be found in most coastlines throughout the world. Although they’re portrayed as one of the more aggressive sharks on shark week, they are incredible creatures to see underwater and shouldn’t be missed. And there’s literally no better place to dive with bull sharks than Fiji – where you’ll find the biggest bull sharks in large numbers.

With the establishment of the Shark Reef Marine Reserve, Beqa Lagoon has become a premier shark diving area the world over. Bull sharks are the stars of the show here, but divers can encounter up to 7 other species as well. These include sickle lemons, gray reefs, nurse, blacktip reefs, whitetip reefs, silvertips and tiger sharks. With more than 20 dive sites in the lagoon, divers can fill a week or more with fantastic shark sightings. Although you will see sharks during any month of the year, July to September offer the best diving conditions in terms of visibility, water temperature and other large marine life.

As an added bonus, any diving done in the Shark Reef Marine Reserve finances shark research and compensates local fishermen for lost income due to the creation of no-take zones. It’s a win-win-win for sharks, divers and the local population!

A recent study in Fiji found that bull sharks form friendships with each other! Researchers studied data collected over 3,000 shark dives in Fiji’s Shark Reef Marine Reserve (SRMR), one of the world’s most sought-after diving destinations. SRMR is located in the Beqa Channel, off the southern coast of Viti Levu, and is a striking example of collaboration for conservation.

The shark is revered by local Fijians and legend has it that Dakuwaqa, the ancient shark god, provides protection for the people when at sea. So not only will you be exploring Fiji’s underwater world with your dive buddy, but you will likely encounter a pair of bull shark BFFs on your dive too!

View Dive Resorts in Beqa Lagoon

Other Bull Shark Hotspots:

  • Bimini, Bahamas
  • Playa del Carmem, Mexico
  • West Palm Beach and Jupiter,Florida
  • Protea Banks, South Africa

Image Credit: Neil Andrea and @juliesharkangel

Great Hammerhead Sharks – Bimini, Bahamas

PADI Diving Certification required: Open Water Diver or Freediver

Other Shark Species You’ll Encounter:  bull sharks, lemon sharks, reef sharks, nurse sharks and don’t forget the shark’s close cousin… the eagle ray

Bahamas makes it on our list twice thanks to the incredible conditions underwater (there’s actually a color named Bimini Blue), and the fact the Bahamas plays hosts to some of the most spectacular mega-fauna in the world – including the Great Hammerhead Shark.

There’s no mystery as to how the hammerhead shark got its name! That massive hammer – known as a cephalfoil – makes them one of the most distinctive animals on the planet. And that hammer isn’t just for show… It gives this shark superpowers which means the great hammerheads have seven finely attuned senses plus 360-degree vision (without turning their head!) to be able to avoid divers.  Seeing a great hammerhead is rare as they tend to be quite skittish underwater, so finding a place you can reliably experience them is a rarity.

Every winter from December to March, great hammerhead Sharks gather around Bimini  in large numbers. Naturally shy and reserved, these huge sharks with their odd faces become curious in this location, closely approaching divers. Shark diving is closely controlled due to the area’s marine park status. Although Bimini Island is a part of the Bahamas, it is located just 50 miles from Miami in the United States, making it possible to visit by boat in just three hours from the American city.

The waters of Bimini are warm, clear and typically protected. The shark dives occur in less than 20 feet of water allowing divers and freedivers to enjoy incredible encounters.

Plan a trip to Bimini to see the “hammers” and you’ll likely catch up with bull sharks, friendly dolphin pods, and graceful schools of eagle rays. You’ll feel like you stepped back in time to an island still not heavily commercially developed and traversed by golf carts. Bimini can be explored by divers and snorkelers alike – and is absolutely stunning above and below the surface. Head to nearby Honeymoon Beach to swim with the local group of rays as well – after all, rays are really just flat sharks!

Other Great Hammerhead Hotspots:

  • Southern Florida, USA
  • Rangiroa, French Polynesia
  • Solomon Islands

Image Credit: Joe and Lauren Romeiro

Shortfin Mako Sharks – Rhode Island, USA

PADI Diving Certification required: None

Other Shark Species You’ll Encounter:  blue sharks

Mako sharks get nearly as much airtime on Shark Week as white sharks, thanks to their incredible biology, although the fact they are in the same shark family as whites (mackerel) probably doesn’t hurt!

Shortfin mako sharks are sometimes described as miniature great whites on amphetamines. These toothy sharks look like a shrunken-down version of the ocean’s top predators, but they act totally differently. While great white sharks slice slow, graceful circles around a diver, watching with an inquisitive eye, makos are twitchy sharks, hopped up on adrenaline, that speed past you.

Thought to be the fastest sharks in the ocean, makos have an estimated top speed burst of about 45 mph. They can achieve these speeds thanks, in part, to their ability to thermoregulate – meaning they can warm their body temperatures. Incredible acrobats, like great whites, makos are known to jump out of the water, sometimes up to 20 feet in the air, using their perfectly shaped fins as wings and rudders.

Equally impressive, they have the largest brain to body mass of any study shark as well. So they have it all – beauty, brains and braun.

Makos are pelagic sharks that live throughout the world’s oceans, but there are only a handful of places where you can have reliable encounters with these incredible creatures. Our favorite, most reliable place? Rhode Island. Plus, you don’t even have to be a diver!

Most people don’t think of Rhode Island as a shark-diving hot spot, but during the summer months, when the Gulf Stream moves close to shore, this stretch of New England coastline becomes a haven for makos and other sharks, as game fish move closer to shore. You can even join PADI divers, PADI AWARE supporters and Shark Week celebrities Joe and Lauren Romiero as they film and study the local mako population on their dive charter.

Even if you miss the stars, the equally charismatic blue sharks steal the show.

Other Mako Hotspots:

  • Baja Sur, Mexico
  • Cape Point, South Africa
  • San Diego, California
  • Azores

Header Image Credit: Andy Casagrande @ABC4EXPLORE

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