Great White Mystery?

 
In 17 years of diving with the Great White Sharks at Guadalupe Island, we have learned a lot about these awesome creatures. From not knowing where they are heading when they leave the Island, to thinking they are heading to an area offshore to mate, to finding out that we were wrong on that and realizing that they are actually mating at Guadalupe, we have come a long way.

What never ceases to amaze me is the fact that we keep learning new things and that things we thought we knew were actually wrong. Observing them over time has given us some insights into their behavior and how the relate to each other and how their personality changes as they grow. The most important thing I have learned is that just when you definitively think you know something about them, you find out that it may not always be true.

First I have to make a disclaimer. I'm not a marine biologist, so most of what I know about their biology and migration I learned from my friends who are biologists and study these sharks. What I know about their behavior comes from literally thousands of hours spent observing them, both in the water and from above.

The latest theory that has come into question is how the shape of their teeth changes as they growand the reason for that.

Georgina French, a PhD student at the University of Sussex, published a new study that deals with that theory.

From her paper: Up until now, scientists have accepted that white sharks start out their lives with cuspidate (pointy) teeth, which are thought to be adapted for gripping onto slippery fish. When the sharks hit roughly 3m in length, they’re then thought to develop much broader teeth, which are believed to be adapted for catching and eating marine mammals like seals and dolphins. This shift in diet and tooth shape with age/size is referred to an ontogenetic shift.
 

©Georgina French

Her new discovery seems to be that there is a distinct difference between male and females, something I have never heard before.

She writes: Previous studies of white shark teeth have always lumped males and females in together, despite the fact that they are quite different in other aspects of their biology and ecology. I decided to explore their tooth shape/shark length relationships separately. When I combined all of the data from the photographs, the literature and the KZN jaws, I found startling differences between the sexes.  While males seem to follow the accepted pattern of broadening teeth when they get to about 3m long, females didn’t. Instead, a female of any size could have either broad, pointed or intermediately shaped teeth. Females also didn’t change the angle of their upper third teeth, while males did.

©Georgina French

As with any new discovery, there are instantly a bunch of new questions. In this case, first and foremost, 

What does this mean?

 Broadly speaking, the results indicate that either males and females are feeding on different things as they grow up, or that the tooth shape change isn’t related to diet.
When sharks mate, males hold onto the females using their teeth. It’s possible that the broadening of the teeth and the change in tooth angle found in males could be an adaptation for mating, rather than for handling different prey. Alternatively, females with broad, pointy and intermediate teeth may be specializing on different types of prey i.e. they are polymorphic. I also found significant variation in the size at which males developed their broad teeth, which combined with other evidence indicates that some individuals mature a lot more quickly than others. Polymorphism and differing rates of maturity among individuals can have pretty big ecological consequences, and these factors need to be taken into account in future studies and white shark management.

This is what I love about working and diving with Great White Sharks. Every question that gets answered opens up a lot more questions. I wonder to what new insights about Great White Sharks this new discovery leads to. Maybe we should call these sharks Great White Mysteries instead.

Let's go shark diving and discover new and exciting things about these awesome animals!

Cheers,
Martin Graf
CEO Shark Diver 

About Shark Diver. As a global leader in commercial shark diving and conservation initiatives Shark Diver has spent the past decade engaged for sharks around the world. Our blog highlights all aspects of both of these dynamic and shifting worlds. You can reach us directly at staff@sharkdiver.com.

Blue Sharks Beat the Odds?

This is one of those classic East coast/West coast stories about sharks that fail to address the overall look at the health of a species.

According to Discovery Blue sharks are not as bad off as once thought:

Although many sharks are experiencing population declines of up to 90 percent now, a new study on western North Atlantic blue sharks has found that numbers of the colorful species there are currently down, but not out.

Other reports had concluded that the region's blue sharks were declining by around 60 percent, but the new analysis reduced the estimate by half, finding that populations of the 12.5-foot-long sharks have dropped by only 30 percent since the mid 1950s, when large-scale fishing practices began in that part of the Atlantic.

Editors Note: The main problem with this story is that "localized good news" from a major new source like Discovery gets transmitted to a huge audience. The facts on the ground point to a worldwide Blue shark population that is in serious decline. Especially hard hit off the West coast where these animals have been tracked migrating to Japan and back...mostly migrating to Japan, fewer and fewer animals ever make it back leading to a virtual collapse of the adult population off our shores.

SharkWeek 2008-Shark Diver, Ocean Reef & Bathys Hawaii celebrate

Luke Tipple, Marine Biologist and Adventurer, is developing his own Science based show with GRB Entertainment of Los Angeles. While the show is coming together Luke continues to offer his technical and scientific knowledge to top research and entertainment teams worldwide. This year Luke was asked to be the dive safety officer and shark behavior specialist on Discovery Shark Week's premier show MythBusters.

Since this is Luke's first time on Discovery, and since he is working very hard on a show of his own at the moment Luke's sponsors got together to celebrate by giving away some cool gear.

To win just watch MythBusters on Shark Week during July 28th through August 3rd, 2008, go to our contest page and answer a simple question related to the show (HINT: check out the dive gear… we are his dive sponsors after all!).

You could win the prizes above, a great dive watch, an amazing dive mask, or a chance to get face to face with a great white shark.

On behalf of all of Luke's sponsors, we look forward to seeing him in many more great shows in the future and thank all of his fans for watching, it has been our pleasure to believe in and support Luke's efforts in both entertainment and educating people about sharks and science. Please tune in and sign up to win some great gifts as a token of our appreciation for your support.

Shark Week 2008-Shark Trust Wines

We got the following email from the folks over at Shark Trust Wines. As huge supporters of this plucky shark brand we're more than happy to pass on the offer to our shark fans.

As far as we know this is the only shark branded wine on the planet...this is why we serve it proudly on all our shark vessels:

Greetings!

It's here...our favorite week of the year...SHARK WEEK! Stock up on Shark Trust Wines this week and get ready for 7 full days of shark programming on the Discovery Channel. With every case of wine purchased this week at sharktrustwines.com, we will include a shark topper. No need for special codes online. We will automatically send the topper.

Cheers,
Melanie CEO
Shark Trust Wines

TED-If You Don't Know, You Should

Robert Ballard-Speaking at the TED conference back in 2007. Why are we looking into space when we have unexplored oceans right here?

Join him on a 16 minute trip to 70% of the planet:

"MythBusters Shark Week 2008"

Of course the crew here of Shark Diver knows more about this than we will let on:

On a March afternoon, Savage is busy with a 3-foot-long metal rod, a variable-speed drill and red string. He can't hide the "it's always Christmas Day" enthusiasm on his face as he works on his latest contraption: a device to simulate how an injured fish acts in the water. It is for a myth to be explored in an episode to air on the cable channel's "Shark Week" this summer.

The "Shark Week" episodes will be filmed in the Bahamas. A few weeks earlier, the team was in Alaska to examine myths associated with the far north. The last new episode, which aired Feb. 20, was the show's 100th. A new batch of original episodes will begin airing in July, and the crew is preparing those shows now.

Cool Great White Shark Video

We love John West Tuna commercials. O.k, so the actual tuna is pretty basic, comes in a can, and tastes like...tuna.

But their commercials continue to set the bar for shark cool. First we had the guy inside the Mako, then the crazy Alaskan Bear. Here's the latest installment with a focus on what else? South Africa's-Flying Sharks.

In case you were wondering, there's really no tuna in the world that will make Great Whites sit up and act like this. If there was-the crew here at Shark Diver would have bought into this company a looong time ago!

The Front Lines of Stupidity?