Dead Sharks at the Flower Gardens

[justin-branam]

Very wierd and sad. dont know what the cause is.


here is the link to all of the pics: http://www.digitaldiver.net/yabbse/index.php?board=6;action=display;threadid=6204

 

[archman]

Gads, that's odd. I'm sure Emma and the rest of the Sanctuary gang are making a crapload of feverish inquiries to NMFS right now.
Looks like more than one species of shark. Any estimates for how many were lying around like that?

That's gotta be poisoning or toxicity of some kind. Never seen anything quite like that, though. Why is it only affecting sharks? Or maybe fish died too but floated up and away. They don't usually sink until the decompository gases abate.

Justin you may want to bump this to the marine life or ecosystems forum so some of the non-texas folks will be more inclined to look-see and put in their two cents.

 

[Rick Murchison]

We had a shark kill a few years back around Perdido/Gulf Shores. It was never completely proven, but the general consensus was a shark virus of some sort. It was definitely a disease - but I don't think the agent was ever identified.
Had the same thing with hardhead catfish about three years ago.
Critters get epidemics from time to time, and we find out that what we don't know 'bout those diseases... is a lot.
Rick

 

[archman]

We had a shark kill a few years back around Perdido/Gulf Shores. It was never completely proven, but the general consensus was a shark virus of some sort. It was definitely a disease - but I don't think the agent was ever identified.

Are you referring to this?
http://news.bbc.co.uk/1/hi/world/americas/980115.stm

Hmmm... confined to blacktips and atlantic sharpnose. Is that what the species breakdown was at the Flower Gardens? I thought I saw a reef shark somewhere.
I like the red tide theory. A dense local bloom in the upper water column could very easily account for this... you'd have to recover some sharks and run dinotoxin (and other tox-screens) tests.
I'm a little wary of the "virus theory". There's a lot of this in the literature for marine species, almost never proven and used as a crutch when no other cause is identified. The last few years the "oh it must be a virus" syndrome has been getting increasingly tepid reception in the marine science community. We need more microbiologists to see if any of these theories can be substantiated.

 

[justin-branam]

Can a Mod move this to the marine life forum, Dee?? Thanks.

 

[Otter]

Can a Mod move this to the marine life forum, Dee?? Thanks.

Complete....

 

[mbuff]

Some mistatements in that article, but interesting stuff....

There's a plethora of toxins associated with algae and red tides... if it is an algal bloom it will take some time before they identify the culprit. Any information on the bloom itself? "Red tide," btw can be any number of different species with any number of associated toxins. Sometimes, as in the case of Noctiluca, there is no known associated toxin. And sometimes potentially toxic species aren't even toxic -- a feature of these sorts of algal blooms is that toxicity seems to vary geographically and temporally. I'd be surprised if it was anoxic water also, because the mortality is limited to the sharks.

Anyway, that's my semi-educated understanding There's a neat photo gallery at the Woods Hole website at http://www.whoi.edu/redtide/rtphotos/rtphotos.html

 

[Rick Murchison]

It is the narrow target of the "agent" that points to a disease critter (virus, bacteria, parasite, fungus) rather than a toxin (pollution, red tide, low oxygen etc). Though the article earlier cited wasn't the specific incident I remember (which was in the early 90's if memory serves), I believe it was all black tips in the Gulf case as well. (During the summer of '01 we found three bull sharks who died of unknown causes, but only three, so that didn't cross the "big mystery" threshhold)
The catfish one really had 'em scratching their heads, because in general catfish are the last to go. I don't know if the specific bug was ever identified on that one either.
As I said earlier, there's a huge hole in human knowledge and understanding about these kills.
Rick

 

[archman]

I agree that hypoxia is out. The water's deep, well-mixed, and offshore.
Localized algal bloom's quite possible, whether it be caused by dinophytes, diatoms, cyanophytes, or martian microbes. Usually specific algal groups have characteristic toxins... I wasn't aware Noctiluca even secreted appreciable amounts of it, but being a dinophyte it should carry some dinotoxins (that's what they do).
As for species-specific mortalities (Rick's last post), they can certainly be theorized to be viral/bacterial, but it very often is not the case. Every species has it's own catastrophic vulnerabilities to the odd toxin/chemical. A pile of sick/dead dogs for instance could be linked to CHOCOLATE, copepods will mass-suicide if even a LITTLE petroleum contaminates the water column, Diver X is violently allergic to neoprene, etc... When species or narrow taxa exhibit death or dramatic behavioral/physiological change to an environmental cue (be it chemical or physical), we call them "indicator species." Canaries in mineshafts are a popular example.
You can also have behaviorally induced mass mortalities, which also tend to target very specific taxa. Cetaceans beach en masse because the leader only is sick, or maybe just confused. Schooling bottom feeders like hardhead catfish and goatfishes could all pile up into a nepheloid reducing layer and get wiped out in a few minutes. Reef sharks could all chow down on a large fish carcass heavily biomagnified with dinotoxin and flop over dead.
You can still have mortalities due to illness. It's just nobody hardly ever verifies this. Distinguishing a rapid illness from poisoning is extremely difficult. It's a bit easier to measure the water column for nasty chemicals and run tox screens on commonly occurring nasties. And with sharks... well they're about as impervious to disease as any organism ever created. Remember that stupid shark cartilage craze?

I emailed an inquiry to Emma. Maybe she has more information (assuming the dive boat informed her office).

I Know! It's SEA LICE!

 

[mbuff]

At the risk of continuing off topic...

>diatoms, cyanophytes, or martian microbes. Usually specific
>algal groups have characteristic toxins... I wasn't aware Noctiluca
>even secreted appreciable amounts of it, but being a dinophyte it
>should carry some dinotoxins (that's what they do).

Not all dinoflagellates have toxins... I don't think toxin is "what they do." Toxin has not been found, for example, in genuses Noctiluca, Cerratium, Peridinium and Gyrodinium.... Symbiodiunium is that lil algal partner found in corals and anemones. There are many others which are not implicated in toxin production also. (Cerratium is considered a harmful algae, tho.. because it's structure, which looks like a saw blade in some species, slices up fish gills. yum yum.)

Toxins within the group vary considerably as well. Saxitoxin (from Alexandrium) looks quite different from okadaic acid (from Dinophysis) which is different from brevetoxin (from Karenia) I don't believe they are considered to be the same class of toxins. They certainly have different physiological effects... okadaic acid is the culprit in diarrhetic shellfish poisoning and is a possible tumor promotor. Saxitoxin, on the other hand, causes paralysis and death and has the distinction of havin once been stockpiled by the US military as a chemical weapon.