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 behaviour 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 and 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 approximately two dozen depending on variables like weather and tides but also, the presence of other larger Sharks, foremost of which is the Tigers.
Whereas the Blacktips are largely confined to the shallowest depths, the Greys and Whitetips are most prevalent in 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 and Lemons each.
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 behavioural patterns.
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 70 individual Sharks on a single dive and with 110 named Bull Sharks as of January, 2011, we may well be looking at a population size of in excess of 400 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 behavioural 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, 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!