Blog about "The World's best Shark Dive" by Beqa Adventure Divers.
Featuring up to eight regular species of Sharks and over 400 different species of fish, Shark diving doesn't get any better!
Yes, in theory, one should generally not interfere with Nature.
But in practice, we always do, and this overwhelmingly in negative ways - so the small act of kindness for that little terrified turtle was nice to see.
It obviously begs the question, did the Tiger kill the Manta.
I'm also amazed at those many Reef Sharks as I've never seen them scavenge like they are doing here.
And I must add that all those unprotected punters are a scary, scary sight, the more as Tiger Sharks are known to vigorously defend their meals, and perceived interlopers have already been grievously injured.
Although tiger sharks clearly utilize open-ocean habitats in both Atlantic and Pacific oceans, the majority (78.7%) of satellite location estimates for tiger sharks captured around Maui and Oahu during the present
study were in coastal waters over insular shelf habitat.
Tiger shark affinity for coastal waters and shelf habitats
has been documented in previous studies in Hawaii, Australia, the Galapagos, the Bahamas and Florida,
although movements are generally much wider-ranging over the extensive continental shelf areas off Australia
and Florida, than over the smaller insular shelf habitats surrounding the oceanic islands of Hawaii or the
Galapagos. Conversely, most tiger sharks tagged at Challenger Bank (Bermuda, Atlantic Ocean) predominantly
used open-ocean habitat. These apparently conflicting patterns of open-ocean versus coastal habitat use by
tiger sharks may partly stem from the demographic characteristics of sharks tagged in these different studies.
For example, eighteen (95%) of 19 highly-migratory tiger sharks tagged at Challenger Bank were mature males,
whereas tiger sharks tagged during the current and previous Hawaii studies were mainly (59–80%) mature
females which predominantly utilized coastal habitats, and tiger sharks exhibiting high coastal residency in the
Galapagos were predominantly (85%) sub-adult females and males. These differences in habitat use are consistent with habitat segregation among different life history stages, with sub-adults of both sexes and mature females
occupying coastal areas, and mature males occupying offshore habitats, but likely also reflect the species ability
to adapt the scale and pattern of movements to local resource distribution.
Very interesting! Once again, Hawaii's Shark Research Team has produced a stellar paper focusing on the residency pattern of Tiger Sharks between Kauai and Maui.
Dunno about you - but I just love love love this stuff.
Step by step, all that initially rather baffling local, regional and globalsneaking around is being deciphered, and I'm just totally fascinated by the insights.
Once again, this is evidence for the massive influence of environmental factors whereby both the coastal abundance and swimming performance of those migrating Tiger Sharks are being shown to be highest at ~22°C. Consequently, they track their optimal temperature and are thus more likely to be found in coastal areas in winter in the tropics; but towards temperate latitudes, they are more likely to be found in coastal areas in summer, see the figure at the top - and as climate change continues to heat up the oceans, those tracks are likely to shift poleward with according potential consequences for coastal communities, see the example of Sydney.
Very interesting!
Incidentally, this is very similar to what we are currently experiencing with our Bulls who have been shown to favor a temperature of ~26°C.
As the water temperature at Shark Reef has recently hovered around 29°C for a protracted period of time, the number of especially the larger Bull Sharks has been appreciably lower - and whereas we don't dispose of any strong evidence, it is only fair to speculate that they may have retreated to greater depths or even absconded to places like Kadavu where the water temperature has been significantly lowered by Gita.
But I'm digressing as usual.
Great paper featuring numerous people I like and respect.
Enjoy!
He is disturbing a predation event, and this is agonistic behavior = the Tiger is likely seeing him as a potential competitor and clearly telling him to piss off.
Amazing defensive behavior by the Turtle, too! :)
Now, some Bull Sharks (and possibly Tigers and OWTs?) appear to have attacked and killed a Humpback calf in Haapai, Tonga. Very interesting - and big kudos to the good folks at Whale Discoveries for their impassioned and respectful report.
If I understand it correctly, it appears that the effects of provisioning at Tiger Beach are, if at all, minimal insofar as the Shark diving schedules appear to have an only negligible influence on overall Tiger Shark movements, and as the large majority of individual Sharks did leave for their annual migrations as already described many years ago.
And the four homebodies?
Maybe they just like it there, maybe they're in love with Jimmy or Eli, maybe they're just lazy or maybe that's just the "right" amount of Tigers in that area, who knows - plus, as our own research has shown, residency may be completely different in another year!
Long story short?
This is once again evidence that Shark tourism in general and Shark provisioning in particular appear unproblematic at the ecosystem level whereas at finer scales, effects are, if at all, clearly sub-lethal. Granted it's merely a data point - but the evidence is certainly mounting!
I must say that having gone there several times and never having heard anybody mentioning them, I was totally surprised when reading about the occurrence of Tiger Sharks in the archipelago - but then again, considering the numerous (possibly distinct) Green Turtles and their nesting beaches, it makes total sense!
May this be a rather recent phenomenon like in Cocos where there however were previous reported sightings by Hans Hass and Zane Grey? Considering the tracks, quite possibly - but then again, who knows!
The findings?
Much in line with what has been reported by Adam and Richard in Raine Island = that most Tigers would remain in the vicinity of the Turtle nesting site but that some would roam further. The way I read this, this once again confirms that those Tiger Shark migrations remain highly complicated and mediated by environmental factors - which of course begs the question, what is the influence of the ENSO = there is definitely a need for longer term monitoring studies.
Anyway, very interesting indeed!
Enjoy the paper!
PS - turns out that I've really not been paying attention!
This is BRAT, and at close to 5m, she's now a serious Shark.
Of interest, on top of all those big Shark Suckers, she sports a small white Remora (possibly R. brachyptera*) that you can discern on her chin as she comes in and next to her gills as she swims away.
Kudos to Tumbee for this great circular feed and to the staff for having beautifully contained the Shark's rather epic exuberance.
* Having observed her swimming into BRAT's gill chamber, I now tend towards R. albescens.
Much of it depicts the situation at Raine - including the Turtle lovers, Turtle tagging, Tigers scavenging and finally, Tigers attacking Turtles, and the Turtles' defensive maneuvering.
That's quite a handful of prominent authors - but in essence, this is a re-interpretation of some of the data collected by Richard, Adam and Ian whilst on the venerable Undersea Explorer that have already led to this paper from 2012 I posted about here.
Which is why the authors stress that much of the above is speculation.
The experimental design was aimed at deciphering long-term movements, and the present fine-scale analysis is very much based on inference rather than actual scientific evidence; but having said that, Richard and Adam have logged hundreds of man hours at Raine, and tell me that actual predation events on healthy Turtles are very rare and tend to be confined to the start of the breeding season when there are less Turtles and the Tigers are just arriving hungry. On a busy year, Raine will yield up to 2,000 dead Turtles, meaning that after a while, the Tigers are more than sated and really could not care less about chasing after healthy Turtles.
Like I said, very nice - but now things are changing.
BHP the mining giant is giving a lot of money to the Raine Island Green Turtle Recovery Project, and the island is being made more Turtle-friendly by eliminating features that could kill them and by protecting the nests against inundation. This means that less turtles will have accidents, and that any distressed Turtle will be aided by the turtle lovers and consequently, adult Turtle mortality has already been reduced by 50%.
And the Tigers?
What happens at Raine is part of a system - and if you tinker at one end, it stands to reason that there will be consequences at the other.
Will the Sharks predate more on healthy individuals whilst expending more energy in the process - and if predation increases, will that have an effect on the behavior of the Turtles? Or will the Tiger Sharks gradually stop coming? And what are the effects of this diminishing resource on their population?
Here's what I think - and yes I'm totally speculating.
Research in Hawaii has shown that those Tiger Sharks are able to regularly exploit determined ephemeral resources, and our own observations at Shark Reef indicate the same for our Bulls at Shark Reef. In essence, one of those Sharks will stumbles upon an opportunity, is able to memorize the experience and will henceforth come back to exploit it. This is learned individual behavior, not something that is genetically encoded or communicated by conspecifics or the like.
At the same time, our observations and those of the GWS people indicate that individual Sharks will favor determined strategies, e.g. individual GWS will attack the teaser bait consistently in one determined way; and on Shark Reef where we have a hand feeding and a bin feeding tribe of Bulls with very little overlap, those specialized hand feeding Bulls will gradually stop visiting when we temporarily suspend hand feeding,
Could it be the same for Raine Island?
Could there be always the same Tigers, and could those individuals be specialized scavengers that would not switch to outright predation but instead, would eventually stop coming once there are not anymore enough carcasses to feed on?
Dunno - but that's certainly testable, or not?
And another thought.
If one believes Domeier -and I certainly do- what happens at Guadalupe is essentially a GWS feeding and mating aggregation. Could the food pulse during the pupping season of the Northern Elephant Seals maybe even trigger mating, and could it be important for the success of the ensuing pregnancies?
And could what happens at Raine Island be the same, meaning that if the Shark aggregation slowly disperses, finding mates would become more difficult and reproduction success would be lower?
And here's even a bunch of video clips for the lazier ones among you - from exhaustive to easy all the way to basic. I must say, this is all very impressive indeed.
I cannot find it online - but somebody sent me the full text that says Open Access, so I assume it will appear shortly.
Anyway, here's the
ABSTRACT: Advancing our knowledge of the reproductive biology and mating systems of freeranging
sharks is inherently challenging. The large size and mobility of the specimens are just a
few of the problems that make such studies complicated, and in some respects, impractical. The
tiger shark Galeocerdo cuvier is a large, roving, apex predator found in many oceans throughout
the world. Although their nomadic nature is primarily linked to large-scale migrations, these
sharks can also display site fidelity.
One site where this is known to occur is at Tiger Beach,
Bahamas. Unique to the waters of this area is the consistent sighting of large females. While the
sex-specific use of the area remains unknown, the shallow, warm environment could represent a
critical habitat for reproductive events. To investigate the reproductive biology of tiger sharks at
Tiger Beach, 65 individuals were opportunistically sampled between 2011 and 2014. Reproductive
status of captured females (n = 59) was assessed with ultrasonography and by measuring circulating
sex steroid hormones (progesterone, testosterone and estradiol).
Our results indicate that
Tiger Beach is a high-use site for female tiger sharks of mixed life stages. The results also suggest
that Tiger Beach may function as a refuge habitat, allowing females to reach maturity free from
male mating harassment, as well as functioning as a gestation ground where gravid females can
benefit from year-round calm warm waters, which may reduce the gestation period and accelerate
embryo development.
I really like this, especially the collecting of multi-pronged evidence.
Local lore had it that the Tiger Shark aggregation was correlated with the fact that Sea Turtles would shelter on Little Bahama Bank during rough weather - but I guess we now know this to be, if at all, of only secondary importance.
Press release here.
