Do Bull Sharks have Friends? New Paper!

Spoiler: maybe yes maybe not!

Remember Mike's speculative hypothesis?

In brief, I opined that as their prey is comparatively scarce, evolution would select for large predatory Sharks to be solitary in order not to have to share their kills. 

But whereas that appears to be largely correct for Tigers and Whites, anecdotal evidence and some papers (and here) indicate that Bull Sharks appear to mostly travel in pairs or small groups, and I was eager to see whether our enormous data base could help shed further light on the issue. Yes our Shark feed is obviously an artificial aggregation - but I speculated that if certain individuals would preferentially turn up together, this might be a strong indicator that they might also be traveling together when not attending our dive.

The initial findings were promising.

The data showed some unequivocal, albeit rather weak long-term associations as illustrated e.g. in the following sociogram.

 

Sociogram depicting the social ties between individual bull sharks observed on the study site on ≥34 dives for the time period from 2011 (C). Only GAI values in the highest 30% were included to highlight the strongest associations between dyads, with thicker edges indicating higher GAIs for both individuals observed throughout the entire sampling period (red nodes), and individuals which were not observed throughout the entire sampling period (blue nodes) - click for detail.

 

Impressed? 

Me too, initially - but then came the crux with the bloody interpretation!

Did those Sharks really turn up together because they like each other? Or was it because their core ranges overlap with the Shark Reef Marine Reserve = they just happen to live in the vicinity? Or because they share some behavioral trait that makes them bolder/more curious/more opportunistic/weaker hunters = more prone to visit our feed? Or are they maybe the remnants of a cohort of siblings who stayed together in the river nursery and have traveled together ever since? Questions questions!

Short answer: who knows - which is kinda disappointing!

But, we now have a starting point.

Those numbers in the sociogram all correspond to known individual Sharks, and somebody could now invest some time into observing how they actually interact during the dive - and assuming that the visual observations confirm the initial evidence, one could then try and equip selected individuals with adequate sensors like cameras and/or say, business card tags to see what happens once the Sharks leave Shark Reef and/or take tissue samples to determine their relatedness, etc.

Yes that's a lot of work - but that's what we do, so keep watching this space!

Long story short, so far so good!

Enjoy the new paper! 

 

PS - Juerg here, courtesy of Tom.

IMO the semantics are a lot of splitting of hairs (= do we KNOW that they're not friends?), the more as I believe that some are, and that some (like Blunt and Maite) are very much the contrary - but then again who am I to say!

So thanks for the publicity, much appreciated!

PPS - another really nice piece here - well done!

Heinous Robbery - Video!

Watch - story here!
And would that scene at 2:15 qualify as a true Shark selfie?

The perpetrator is a pesky and so far unnamed little guy.
Suggestions welcome - or better yet, officially name him yourself once we identify good permanent markers and Tashi puts him up for naming!

Anyway, it was epic.
Bravo, and a huge Vinaka Vakalevu to Silio for having retrieved the rig - and a big tip o' the hat to  Tovatec for their venerable but utterly phenomenal Galaxy 2500s that survived the ordeal completely unscathed! 

Enjoy!
 

Saving Our Sharks - Video!

Obviously don't fully agree but still, quite good - click for detail. Source.

This is great and important work.

Huge kudos to Chino and Luis, and also to all the other people, dive shops and sponsors of Saving Our Sharks who have contributed to this success.

Enjoy!

Bull Shark vs hooked Shark!

Yes Bull Sharks got big sharp teeth - great pic by Sasha! Click for detail!

Behold!

Story here.

Not at all sure about the first Shark - but the big one is unmistakably a Bull = a species that will most definitely prey on other Sharks.

Enjoy!
 

Bull Shark on Steroids!

Wow.

Never seen such a fast Bull Shark!

Apparently somebody was bottling, and apparently this is from the far South of the Maldives where there is zero evacuation in case of an accident.
H/T Daniel!

Anyway, enjoy!

Bull Shark vs Boat!

Cool.

The behavior is certainly unusual - and no, I'm not gonna try and interpret it. :)

Story here - enjoy!

Bull Shark vs Hippos!

Source - apparently this is not too rare!

Feisty feisty!
Enjoy - story here!

Sharks vs Humpback Whale!

Wow.

Remember this paper about Bulls killing a Whale?

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.

Bulking up at Shark Reef - Paper!

Great stuff - and I cite,

With provisioning occurring 3–4 times per week at the SRMR and focal individuals consuming an average of ~0.74 heads per provisioning day, we estimate that these sharks consume ~2.6 provisioned tuna heads per week, which is similar to our estimate of food required to meet their weekly energy budget (2.3 heads per week).
As such, it appears that our focal sharks may be fuelling their energy requirements exclusively from provisioning. However, considering that encounter rates vary widely among individuals and between months and that electronic tracking data show that individuals intermittently leave the area for a few consecutive days, weeks to months throughout the year before returning to the feeding site (Brunnschweiler et al., 2010; Brunnschweiler & Barnett, 2013), at the most this may only be the case for some individuals at certain times of the year (e.g. at the beginning of a calendar year).
....
The foremost limitation to this study is that data and inferences are based on 10 individuals observed on 36 days. 
These 10 individuals may be bolder than other bull sharks encountered at the SRMR and thus predisposed to take food and, hence, the patterns found for these individuals may not reflect all the bull sharks in the area. Given the variable number of sharks at feeding events and days individuals are absent from feeding events (Brunnschweiler & Baensch, 2011; Brunnschweiler & Barnett, 2013), further work is needed to determine the importance of tuna heads compared with natural prey in bull shark diets, for example, stable isotope analysis.

So there you have it.

Very surprisingly indeed, those Tuna heads we feed are not at all rubbish but instead a valuable supplement that can help bulk up our Sharks when they come back all exhausted and emaciated after the pupping and birthing season - and I can fully confirm that we've seen many an individual Shark become chubby and happy again after only a few visits!

But what about the potential negative aspects?

Could we be overfeeding them, and could we be subtracting them from the regulatory role they got to play in the environment?

Likely not, as a) the feeding frequency is not uniform but highly individual and determined by individual dominance and/or boldness, b) our observations tell us that those same dominant Bulls do not simply gorge themselves but clearly stop feeding once they got enough and c) our Bull Sharks are not resident but only sporadic visitors whereby individual site fidelity and thus residency is by no means uniform let alone increasing but instead varies greatly from year to year - re-read this post and paper!

But that's obviously not hard evidence but (highly) educated guess.

Hence the suggestion that one examine the Bull Sharks' diet via e.g. stable isotope analysis - and without wanting to preempt anything, I can state with great confidence that you will need to keep watching this space! :)

And this stupidity with its even stupider title?

Re-read this: the actual problem is not the provisioning per se but the disturbance of the Whitetips' diel rhythm, and not the fact that they are being fed but instead, the fact that they are not getting enough food and are incurring a metabolic loss as a consequence! 

Incidentally, much like at those cage dives where in their collective wisdom, the regulators have decreed that the GWS must chase teaser baits without ever being fed - and even more so in e.g. Shark Alley where they are being lured into wasting heaps of energy on fruitless breaches so that the photographers can get their shots!

Detail detail!

But I'm digressing as usual.

Enjoy Juerg's paper (and here)!

Bull Shark vs Spearo!

Wow - watch.

A shame for the Shark.

But that's one helluvan aggressive animal and the reaction by the spear fisherman was definitely in self defense and meant to only fend away, the more as he did not fire the gun.

Story here, usual reactions here.

Playa Sardines!

Charlie with one of his girls. Source.

So, I finally went diving with the Caribbean Sardines.

It was great.

Of course I dove with  GSD member Phantom Divers and I must really say that Chino has created an awesome slick, professional, fun and above all, very safe Shark diving machine that is among the best I've experienced anywhere - and yes, witnessing Charlie, and Ramón with their babies has been a special privilege.

Plus, progress on the conservation front has been simply stellar.

Under the leadership of its new full time director Luis Lombardo, Saving our Sharks is progressing from strength to strength, with more than 40 dive shops and dozens of boat captains observing the code of conduct and contributing funds, with substantial money going to fishermen in exchange for not fishing Sharks, with continued research and public presentations by Shark researchers, and with massive outreach to the public and to schools.

Bravo!

And then there was that remarkable tooth.

A present by Ramón who collected it right in front of me, it looks totally different from any Bull Shark tooth we've ever found here in Fiji - and trust me, we've found a few! 

It's the tooth on the left, together with two large Fijian ones - and considering that those Caribbean Bulls are a distinct genetic population with individuals that are notably smaller than those in the central Pacific, its size is simply spectacular. But then again, those are Mexican Sharks - small in size but packing a mighty punch! :)

Click for detail!

Anyway, nice to be home again.

It's the low season when the pregnant Bulls travel to the rivers to pup whilst the others are getting ready for mating and in turn appear to lose their appetite for juicy Tuna heads - but we've got heaps of other Sharks, and this also gives us a chance to focus on the countless Fishes.

It's already hot hot hot - so here's to a tropical depression to suck away some of the heat, as parts of Fiji are already experiencing dangerously hot surface waters.

But that's the topic of another post.

To be continued!

Are Bull Sharks particularly aggressive?

Of course not!

In fact, rather the opposite!

Contrary to much more assertive species like e.g. Silvertips, Galapagos' and Grey Reefies that have no qualms approaching, and sometimes even harassing SCUBA divers, Bulls are much more wary and appear to actively avoid us, to the point that they will generally only approach people underwater when attracted by food. I call them shy bodybuilders - but bodybuilders they are, large and immensely strong, and they definitely demand to be always treated with great circumspection and respect!

And the numerous bites?

Like our newly minted sharxpert (my oh my! :) ) Lindsay explains, Bull Shark habitat coincides with the areas most frequented by people, meaning that the chances for encounters are comparatively larger - and then, everything goes, from mostly nothing to mistakes to agonism (= aggression) all the way to outright predation = not aggression! 

But yes - forget the legends about the exceptional aggression, the testosterone and the high territoriality that are nothing but unsupported BS!

Anyway, just saying!

I was away and have only now seen Lindsay's interview, and wanted to state that I very much agree. Nothing beats personal experience - and that she certainly got!

Attagirl - well said!

Cocky Tiger in the Bahamas!

Source.

Just got this e-mail from El Diego.

Have you seen this?
The Tiger could try that with Nica, Monica or Blunt and see how it goes hahaha.

Or Chica!

She came back yesterday after a three-week hiatus whith the obvious urge to reassert her dominance around the suspended bin - and reassert it she did, to the point that for the first time, we were able to witness a targeted attack by a Bull Shark on a conspecific that had the bad idea to barge in and try and steal a Tuna head! Our big Fiji Bulls are nothing (!) like those Bahamian Sardines - and we got the science to prove it!

Anyway, interesting video.

Enjoy!

Migrating Bull Sharks in Australia - Paper!

Read this!

Very interesting!

If I compare what is happening on the East coast of Australia with our observations, I would not at all be surprised if our Bulls displayed the same behavior! 

We know that they are not resident, and although overall, they spend more than half of the time inside of the Fiji Shark Corridor, individual differences are very pronounced and sometimes, certain individuals disappear for weeks if not months which could very well be due to the fact that they may be engaging in prolonged and wide ranging migrations - certainly within Fiji and quite possibly, albeit much more rarely, even further as documented by that genetic analysis from 2012 . 

And then, there's that mysterious regular dip in numbers in April which leads me to believe that something attractive is going on elsewhere, possibly some irresistible spawning aggregation or the like.

Alas, it doesn't look like we're gonna find out anytime soon.

Our Bull Sharks are our pals, and we will neither fish them in order to screw on SPOT tags or insert tags into their abdominal cavity, nor will we tag them conventionally as long as the process will condemn them to a life carrying those anchors that keep irritating the muscle tissue.  

Years ago, I was hoping that somebody would develop a less invasive attachment - but I've resigned myself that most Sharks are not tame like ours that can be tagged on the fly underwater but that instead, they need to first get caught. And then, the new SPOT tags with single bolts and/or the insertion of the acoustic tags are perfectly OK, meaning that realistically, nobody is gonna bother developing something specifically for an obscure micro-project in Fiji.

C'est la vie.

All our research has always been conducted on a need-to-know basis, i.e. initially in order to investigate the effectiveness of the SRMR and later, the Fiji Shark Corridor in protecting our Sharks, with the result being that it ranges from excellent for e.g. the Reef Whitetips to satisfactory for e.g. the Bulls to poor for the Tigers. 

And now that the SRMR is cemented into law, the next challenge will be to determine the most efficient and effective way to optimize that protection by enacting Fiji-wide conservation and/or management measures. No I'm pretty much certain that it will not be a Sanctuary so you guys out there, please don't bother as all you will achieve is to piss everybody off and likely make matters even more difficult than they already are. If at all, there will be a Fijian solution - something that will take time and patience, and require that all stakeholders get something and nobody everything.

And I will certainly leave it at that.

But I'm obviously digressing.

To be continued no doubt!

Reunion - first Insights!

Source.

Do you speak French?

If so, watch this.

If not, try Google-translating this. 

Some of those preliminary results are rather surprising, and I look forward to hearing whether those insights will be confirmed as the research continues.

Bon film et bonne lecture!
 

Shark ID - Help wanted!

These are Bulls Sharks - click for detail!

Check this out!

What are those Sharks among those Grey Reefies?

Methinks Dusky/Galapagos (but possibly Bronzie?) and.... Pigeye (!!!) - the latter because she doesn't feel like a Bull, and because I read that from C. amboinensis, the bull shark differs in its lower, less erect first dorsal fin and higher, more erect second dorsal fin. The ratio of first:second dorsal height is 3:1 or less in C. leucas, but over 3:1 in C. amboinensis.

Opinions please!

JSD - David?

Pelagic Bull Sharks?

Wow.

If you can, please watch this.

Yes it's long but well worth the effort.

I'm stumped by the revelations at the end.

Apparently, Reunion's Bull Shark are not resident but only seasonal and apparently, they could be spending a large amount of time in the open ocean.

If so, this would mean a big shift in what we know about this species.

Or maybe not. 

Maybe this is simply more evidence for the environmentally mediated behavioral plasticity I've posted about here. Maybe those Bulls rely on migratory prey and only return to Reunion to mate - think of Playa where contrary to Fiji, there is merely a short Bull Shark season that is being linked to reproduction and where so far, nobody knows what they do during during the remainder of the year.

Maybe.

And the hypothesis of heightened aggression during the mating season?

Not convinced. Aggression is not predation and to me, those described strikes point to predatory events rather than agonism. Plus, our Bulls don't feed during mating season - but then again, this applies to Fiji and maybe, those Bulls behave completely differently!

Long story short?

It is complicated!

Feeding Lionfish to Bull Sharks?

Source.

Watch this.

So Cassell is back.

Which immediately begs the question, with or without Spot's fins?

But I'm obviously digressing.

The uncontrolled feeding of Lionfish to Sharks is a bad bad bad idea - the more as contrary to Playa where they encounter female Bull Sharks that are indeed conditioned and rather mellow, the Bulls in Cancun are feisty males that have already bitten people. With that in mind, does anybody think that the authorities are gonna be as delighted as Cassell appears to suggest?

Having inquired with a friend, his answer is

Hola Mike. I tried to feed lion fish to the bulls and they spit them out. Nobody is feeding in Cancun because it is a marine park and it is not permitted. Actually i don't think these guys have a permit to do what they want.

And why am I not surprised - caveat emptor!

To be continued no doubt!

PS! - less than a day after posting this, the video has been made private...
As I said, caveat emptor!
PPS - as per the comment below, the video has been re-edited and re-posted!
PPPS - and now the video has been retracted. Wow.
 

This will get you killed!

Source.

Watch.

From what I understand, this is precisely what has led to the death of Markus Groh - same species, diver way too close to the bait crate and way too passive, stirred up sand.

Need I add that this is not sustainable?

Oh well - others are already looking into this stuff.

Saving our Sharks: Shark Diving Protocols!

Chino - indefatigable and very much the mastermind behind these positive developments!

Bravo!

This is an excellent list of rules.

If everybody diving with the gorditas in Playa abides by those common sense protocols, some of the past conflicts will be greatly reduced, and everybody will be able to deliver a memorable, exhilarating and above all, safe experience to the clients!

And in the process, everybody will be earning a stable income for many years to come!

Great job.

Kudos to SOS, Razonatura and especially, Ixchel for a job very well done!

And here's another video - with suicidal turtle!

Enjoy!