Lemon Shark in black and white

Sharks

Great hammerhead shark off Bimini
Great hammerhead shark off Bimini

Great hammerhead has low genetic variation

Genomic data reveals historical population declines and high levels of inbreeding in great hammerhead.

In a recent report by the IUCN Red List of Threatened Species, 31 percent of all shark species are threatened (Critically Endangered, Endangered or Vulnerable).  In 1980, only 9 species of oceanic sharks and rays were listed as threatened.

Lemon sharks doing ... erh... something. A cobia is joining the merry-go-round
Lemon sharks doing ... erh... something. A cobia is joining the merry-go-round

What do sharks do all day?

What do sharks do when we’re not looking?

To answer this question, Murdoch University fish biologist Lauran Brewster attached accelerometers to the fins of 24 lemon sharks in the Bimini Islands, Bahamas to find out.

Similar to our wearable Fitbits, the accelerometer collects data about the sharks’ movements, which are then analysed using a statistical approach called machine learning. “Very basically, machine learning is a model that learns patterns in data and can be used to identify similar patterns in new data and make predictions from it,” said Brewster.

Shark diving.
On a shark dive

On Shark "Feeding" Dives

Shark dives provide an excellent way to meet a lot of sharks, and represent a unique situation in which sharks are treated well by humanity.

Shark dive clubs usually bring some fishy scraps—in most cases the remains left over after big fish have been cut up for sale. The scent attracts the sharks into view, and provides a bit of excitement as the animals investigate and try to get a piece.

Tiger shark
Tiger shark

Shark and ray populations in Northwestern Atlantic are recovering

The shark and ray population in the north Atlantic are in recovery, according to a recent study published in the Proceedings of the National Academy of Sciences (PNAS) journal.

Lead author Nathan Pacoureau, postdoctoral research fellow at Simon Fraser University (SFU), and his team came to this conclusion after analyzing trends in fishing pressure, fisheries management and population status for wide-ranging coastal sharks and rays in the western Atlantic Ocean. 

Many species of sharks, including the lemon shark, are known to actively prefer to be social and live in groups or loose aggregations. Social interaction is thought to be important for the survival and success of juvenile lemon sharks.

Sharks can form social bonds

Sand tiger sharks, top predators that live in coastal waters off the Eastern United States, have experienced drastic population declines over the past several decades. Understanding how these sharks move and interact could help biologists better conserve this species and determine how vulnerable they are to human activities. During summer, the sharks congregate in the shallow waters of Delaware Bay but are highly migratory, travelling as far south as the Carolinas and Florida during the winter and early spring.

Salmon Sharks of Alaska

Salmon sharks lack a nictitating membrane, so their eyes can be seen following a subject, Port Fidalgo, Alaska, USA. Photo by Jennifer Idol.
Salmon sharks lack a nictitating membrane, so their eyes can be seen following a subject, Port Fidalgo, Alaska, USA. Photo by Jennifer Idol.

Sharks elicit strong emotions, be it the thrill of a planned encounter underwater or fear propelled by social media and lack of information. Of the more than 400 species of sharks, it is the small family of mackerel sharks that is most iconic. These sharks prompted me to share why one of them, the salmon shark, is an especially remarkable species.

White shark at Guadalupe
White shark at Guadalupe. Are they now going to be poached?

Closure of Guadalupe Island for divers cause of great concern for the sharks

This action expands on the 2022 closure of the Guadalupe Island Biosphere Reserve by the National Commission of Natural Protected Areas (CONANP), the federal agency tasked with managing Mexico’s protected natural areas.

They also closed the island to cage diving in 2021 and the pandemic closed down operations in 2020.

Nurse shark
Nurse shark

Some sharks return to the same sites to breed for decades

Scientists with the New England Aquarium found that nurse sharks, Ginglymostoma cirratum, returned to the waters off the Dry Tortugas, 70 miles (113km) from Key West, to mate for up to 28 years. The Dry Tortugas has been known as a courtship and mating site for nurse sharks since 1895.

A 30-year (1992–2021) study documented long-term site fidelity to this area, with data from 137 adult sharks.

Sixgill and Sevengill — Ancient Sharks in the Kelp

It certainly looks “prehistoric”—whatever that means. Cigar-shaped, blunt-snouted, with that slightly “sock-puppet-looking” smirk, the overall look of this big beastie is very much that of an ancestral shark, like some of the deep-water dogfishes, the sleeper sharks and others. Indeed, fossil remains similar to modern sevengills and sixgills are known from the Jurassic and perhaps much earlier.

Great White Shark  Photo:  Elias Levy
Great White Shark

Great white shark swims more than 10,000km in 150 days

Researchers from the New South Wales (NSW) Department of Primary Industries (DPI) and Deakin University fitted an adult male shark with a pop-up satellite tag and tracked it for more than five months.

After being tagged, the shark swam more than 20km out to sea, then headed north to Queensland. 

It roamed between 80 and 280km offshore between Agnes Water and the southern end of the Great Barrier Reef, before heading to the cooler waters in southern NSW, Victoria and Tasmania.