Monday, April 20, 2009

About our Sharks

Pic: Adi by Michael Aw

More Sharky stuff from our new website.

Welcome to our Shark Diving pages!

This is what has made us world-famous and this is likely the main reason why you have decided to consult our website.
Good choice!

First and foremost, forget everything you may have seen on other Shark dives!
The Shark Dive is like nothing you can experience anywhere else - guaranteed!

Contrary to regular SCUBA diving, there is no pre-determined set of guidelines governing Shark diving as all Shark diving protocols are always highly situation-specific.
Each operator must devise his own set of diving and safety procedures depending on the individual locations, the species mix and other variables, foremost of which very personal considerations - like one's experience and beliefs on the matter in terms of what one is aiming to achieve, how and why. For us, the latter is first and foremost Shark Conservation and Shark Research and the Shark Dive is merely a means to facilitate that goal.

All of that is explained in the following sections "About diving with Sharks" and "The Shark Dive" and also in the pages devoted to Shark Reef Marine Reserve and the Fiji Shark Project. We strongly recommend that you familiarize yourself with the contents in order to be best prepared for this unique and exhilarating experience!

When it comes to our Sharks, you have the chance of seeing the following 8 species:

Whitetip Reef Shark (Triaenodon obesus)
Blacktip Reef Shark (Carcharhinus melanopterus)
Grey Reef Shark (Carcharhinus amblyrhinchos)
Silvertip Shark (Carcharhinus albimarginatus)
Tawny Nurse Shark (Nebrius ferrugineus)
Sicklefin Lemon Shark (Negaprion acutidens)
Bull Shark (Carcharhinus leucas)
Tiger Shark (Galeocerdo cuvier)

We are maintaining an exhaustive database about our Shark dives and as of January, 2009, we dispose of over 2,000 complete data sets. This enables us to run statistical models in order to try and figure out whether there are any recurrent patterns governing the presence, and behavior of our Sharks.
However, weather patterns in the South Pacific are subject to wide year-to-year variations due to the influence of the El Niño Southern Oscillation. It is only fair to assume that this will also influence Sharks as part of the Marine Ecosystem. Many more yearly data sets will have to be collected in order to hopefully once largely take this specific variable out of the equation.

So far, preliminary insights can be summarized as follows.

Our Whitetips, Blacktips and Greys are resident and can be encountered at any time during the year.
Numbers vary between just a few and approx. two dozen depending on variables like weather and tides but also, the presence of other larger Sharks, foremost of which the Tigers.
Whereas the Blacktips are largely confined to the shallowest depths, the Greys and Whitetips are most prevalent at 10m but will occasionally venture down to the Arena at 30m.

The Silvertips, Nurses and Lemons are what could be called "regulars".
They probably live in close proximity to the feeding area (maybe deeper in the Beqa Channel) and turn up shortly after we enter the water. With the exception of the Nurse Sharks which are nearly always there, their appearance is more sporadic and not -yet- predictable.
As with the other Sharks, numbers vary: up to fifteen Nurse Sharks and up to six Silvertips or Lemons. Like the Bulls, these species are confined to the deeper reaches of between 15 and 30m.

Our Bull Sharks are the stars of The Shark Dive and we have devoted a lot of resources in trying to better understand their behavioral patterns (click on image for bigger resolution).
In general terms, they turn up in ever increasing numbers in January and are very consistent through August where numbers start to dwindle in view of their birthing and mating season in October-December where one is likely to see only a few individuals, most of which sub-adults.
Maximum numbers during January-April can be as high as 40 individual Sharks on a single dive and with 47 named Bull Sharks as of January, 2009, we may well be looking at a population size of in excess of 100 individuals.
As with the species above, the Bull Sharks are not residents of the diving area but ascend from deeper water once we start the dive and "call them in" by baiting the ever-hungry Giant Trevally and Red Bass.
We have learned to distinguish between "regulars" that turn up very frequently, and more transient individuals that are individually known but only turn up sporadically. In very general terms, we are however witnessing some sort of "rotation" by all Bull Sharks, whereby individual Sharks will turn up for one week to ten days and then disappear, only to turn up again weeks, or even months later. This may be an indication for the size of their range (probably not a territory, a term that implies that it is defended against conspecifics) or it may be an indication that they are not really bound to any range or territory at all but roam freely throughout the whole archipelago instead.
So far, the data we have collected via our satellite and acoustic tags are not sufficient to precisely interpret this rather surprising behavioral pattern, but they are nevertheless a good starting point for formulating advanced and testable hypotheses .

When it comes to our known five Tiger Sharks, the data collected so far are rather inconclusive.
Preliminary evidence suggests that they are less prevalent during the top Bull Shark period of January through April. The reasons for this are unknown and subject to speculation: it may be due to the overwhelming presence of the Bulls acting as a deterrent, or it may be due to some regular occurrence like their breeding cycle or other seasonal feeding opportunities elsewhere, like the flooding of rivers during the wet season, Turtle aggregations etc. Again, this is pure speculation and would have to be confirmed by e.g. obtaining further insights into their seasonal geographic movements via acoustic and satellite telemetry tools.
Once the Tigers turn up, they will make regular, although sporadic appearances, this probably due to the very large area they are known to patrol. Of interest, they mostly turn up during our second, shallower feed.

All-in-all, we believe that The Shark Dive is well worth a visit year-round.
What is certain is that every single dive is different - but always exciting, intriguing and highly rewarding!


chib said...

Thanks for good information about sharks. But, I will never dare to step in water where shark has been seen!!
I have seen people who had terrible injuries from sharks in Eastern Africa coast. Wouh

DaShark said...

Whow, Tanzania!
Thank you for visiting!

Agree completely, if you're scared of Sharks, don't go there!

Having said this, this blog is about diving which is a wonderful activity!
Once you learn the skills, you have the chance of encountering the animals in a totally different and much much safer way!
Thousands of people do that every year and very much enjoy the experience!

If you have a chance, give it a try!