7 Jun 2009

Dress in blue, tell two...

Two what? Tall fishy tails? Aquatic factoids? Conservation tips?

I've been asked for a few to help prepare for World Oceans Day... so here goes!

Funky fishy factoids:
  • Many sharks have a rather unique reproductive system: they're ovoviviparous! O.k. as that term probably won't mean much to non-biologists so I'll explain. Ovo = egg, vivi = alive, parous = birth. Fish (and birds and reptiles) are oviparous i.e. they lay eggs. Mammals and some sharks are viviparous i.e. mothers gestate their young within a placenta and the young are subsequently born fully formed. So ovoviviparous is like a combination of the two. Imagine the embryos being protected by egg sacs, but instead of laying the eggs, the mother shark keeps them within her uterine cavity until birthing time. In some cases (such as makos, nurse sharks or sand tigers -pictured, from NatGeographic.com) the embryos actually swim freely (no more egg sac) within the uterine cavity. This can lead to uterine cannibalism... i.e. the first shark out of its egg sac will feed on the others. Talk about sibling rivalry!
  • And speaking of shark... have you ever eaten one? I can pretty much guarantee you have! What's that? "Never" you say? HA! Ever had a can of tuna? Voilà! You've eaten shark! Those old enough will remember all the "Save the dolphins" anti-tuna-fishing campaigns some 20-30 years ago. I just remember the explanation of the "dolphin safe" symbol on tuna cans. Well nobody ever bothered to ask for "shark safe" tuna!!! The basic problem with tuna fisheries is that they go out with these enormous nets and circle around a school of tuna. Now tuna don't usually hang out alone. They're following smaller fish species in the hopes of a decent meal. And they're not the only ones. Many species of dolphin prey on the same fish as tuna do, ditto quite a few sharks (and seals and birds etc.). And then there are the bigger sharks crazy enough to try to actually eat a tuna (ever seen a tuna? damn thing's scary and huge!!!). So all these critters are going to get caught up in the same net. Now the fishermen make an effort to get the dolphins out of there ("dolphin safe" remember, still not 100% effective), but no one asked them to do that extra effort for sharks. So what happens to them? Well, a shark is a fish (almost) like any other, and perfectly edible (and some can be quite tasty although I've never had the pleasure). So they just chop 'em up and mix 'em in with the tuna that's headed for the cans. Now in principle this wouldn't be that big of a problem (depending on the species, some are endangered), there are shark fisheries after all, they're edible animals and are avidly consumed in many parts of the world. Scientifically the problem is we have no bloody idea just HOW MANY sharks die each year in this manner. Why is the number important? To establish quotas. To be able to tell fishermen "you can't catch more than this many of a given species each year 'cause otherwise there won't be enough of them left to re-establish the population". And sharks, being mostly big and at the top of the food chain are slow growers and not very frequent reproducers. In other words high risk species when it comes to over-fishing.
  • Orcas (killer whales) are dolphins! Well, they belong to the dolphin family, its largest member! ;o)
  • If you cut a starfish into pieces... you get that many new starfish! As long as each piece has a bit of the center, it will grow back the rest of the body! (but don't try this, it's still painful!)
  • A sea anemone is basically a jellyfish turned upside-down and stuck on a rock! :p (well, it's a bit more than that, but they are close cousins) Also, anemones can move! Anyone who's had one in a fish tank (or gone regularly to an aquarium) can attest to the fact that anemones do get around (albeit very slowly).
  • The Great Barrier Reef can be seen from space! Coral reefs are made by millions of tiny polyps which are basically teeny-tiny anemone. They are unique in that they live in symbiosis with a single-celled algae Zooxanthelle which does photosynthesis and provides them with food in the form of waste products! This relationship is why coral reefs are in such danger from Global Warming, the algae are highly susceptible to temperature fluctuations and if the temperature increases by a couple of degrees they die, leaving the polyps without a source of food.
  • Many fish can change sex at some point in their lives! For example clownfish. In Disney's Nemo, when Marlin's wife gets killed by the shark and he's left alone with the anemone and a single egg (Nemo), well to be biologically correct he should have changed into a female and then taken another male as a mate! Oh, an addendum: male and female clownfish mate for life (so the male only changes sex if his mate dies)! And if the couple live alone in a small anemone (as opposed to this picture) then you can easily ID the two sexes: females are bigger than males!
  • I don't know if this is true in other countries, but in Belgium fishermen frequently measure the size of their catch in beer cans. Unfortuntately the animal's true size many vary depending on whether those were full or empty cans! ;o)
For more oceanic facts check out MarineBio here. Personally I like this one (reminds me of my thesis): "A mouthful of seawater may contain millions of bacterial cells, hundreds of thousands of phytoplankton and tens of thousands of zooplankton."

Want to know more about sharks? Southern Fried Science has a very interesting post on "Four Things You Need To Know About Sharks"

What can I do to help?
  • Keep our beaches clean! See, nice and simple! When you go to the beach be sure to carry back out everything you've taken with you. Don't leave any trash behind that could get swept by the winds and tides out into the ocean... you never know where it will end up and what kind of harm it will do! And it wouldn't hurt to pick up a bit extra either, it might not be your trash, but it's going to harm your ecosystem. Just think: plastic bags last forever... and sea turtles have the nasty habit of confusing them with yummy jellyfish (medusa)! What do you think happens when a turtle eats a plastic bag?...
  • Don't eat shark fin soup! Yeah I know I said earlier that lots of shark species are fished and eaten, but the practice of fin fishing is one of the most cruel there is! Fishing fleets that head out to catch sharks for the shark fin market catch the larger species, haul them on board, cut off the fins, and then toss the animal back in the sea. Why just the fins? Well shark fins sell at a very high price (up to 500$ per fin), so although the rest of the shark is perfectly edible, well he's just not worth as much and would therefore take up valuable space on-board ship. What's the problem with a shark swimming around without fins? Well just the teensy-tiny little detail that the animal can't swim properly without its fins! (never mind the pain and blood-loss from having an appendage slashed off). And a shark who can't swim... sinks (they can't float!). Why is sinking a problem? Scuba divers know this one already. For the rest, well you've dived down to the bottom of a pool, right? How about those ears? Any idea why they hurt? The pressure! Water weighs more than air, and the deeper down you go, the more pressure your body suffers (which is why humans can only dive down so far). Most sharks are adapted to living within a certain depth range, if they go below that then the pressure will kill them. So no fins = no swimming = sinking = R.I.P. For more info on what you can do to help sharks, check out this blog: The Shark Safe Project. Shark fin and shark fin soup photos from
  • Recycle batteries. This might seem obvious as part of the obvious things one should regularly recycle, but this actually important for the oceans! Mercury and cadmium from the batteries make their way into the oceanic food webs, accumulating each step of the way so that the higher up a predator is in the marine food chain, the more likely it is to have high levels of cadmium (if it eats squid and other molluscs) or mercury (if it eats fish). I did my master's thesis on this subject... and it made me not want to eat certain species of fish caught in the North Sea...
  • Ask your local aquarium if there's anything you can do to help out. They usually have cleaning campaigns or awareness campaigns for which they need volunteers. It's a good way to pitch in and give a helping hand, make new like-minded friends, and learn more about the environment!
  • And in general anything that helps reduce the effects of Global Warming will help the Oceans... our first line of defense against this phenomenon.

Any more ideas? I'm going to leave it at that as I'm afraid I'm a little brain dead at the moment... and I still have to put together my Oceanic Blog-A-Thon posts for two blogs!

I'm going to end on an old childhood joke:

"Mom, why are fish called brain food?"
"Because they swim around in schools dear."
(image from NYTimes)

and a question:
"Have you hugged a sea turtle lately?"


  1. Great post - very informative. I now have couple of more fun facts that may help me win at trivial pursuit ;0

  2. Wow! Not that I have ever desired to eat shark fin soup, but now definitely no. What fascinating information, thank you.

  3. I've watched specials about the shark fin problem... sad.

    I've got my blog written and waiting! Some of the things you posted here fall right in line with my essay, so I guess I'm on track... See ya tomorrow for the link!

  4. Awesome post! That was really interesting, though the shark fin thing was scary. I had no idea that people would eat sharks at all, but to just cut off their fins and throw them back is awful! I promise not to eat shark fin soup.
    The clownfish tidbit was a little creepy. It was cool until I thought of Nemo's dad in drag.

  5. Hehe, don't think of him in drag Nicky, it's a complete hormonal change!

    Fish that can change sex are actually hermaphrodites, i.e. they're born with both sets of sexual genes (like snails). Some fish are what we call synchronous hermaphrodites (so are simultaneaously male and female, again like snails) while others are either protoandrous (first male then change to female) or protogynous (first female then male). In the latter two cases when the fish hit puberty one set of sexual hormones dominates and the fish is functionally either male or female. But then depending on circumstances they might change sexes.
    Some ALWAYS change (like grouper) because it's an age thing (at a certain age they switch from female to male, I like to think that since being a female requires so much effort and energy they'd better start out as females when young! lol!)
    Others change because of circumstance, like with clownfish if a male's female partner dies then he will switch sexes. But if he never loses his partner then he'll never switch (clownfish mate for life).


  6. And yeah, the shark fin problem is sad.

    I have no problem with people fishing and eating shark as a whole, considering the amount of meat and fish the world eats... But the idea of carving off the fins of a live animal and then just casting away the suffering animal to its death?! And here I thought humanity was going forward...

  7. What a great post! I obviously love the marine biology, your zest is catchy! I have my post ready, but it's probably not anything close to what others will write about! It does have a sea theme though! I guess I can't give you the link until it's published though.

  8. LOL, I meant to type YOU obviously love marine biology!

  9. lol! Is it that obvious?! ;o)

    I guess you could publish the post, copy the web address and send it to me, and then go in and edit the post by changing the date, say publish time June 8 12:01 AM (just after midnight) and then hit publish again. the post should then appear as "scheduled" and will be live at the appointed time.

  10. I think I'll wait, it's already scheduled. I don't like to publish them and take them off because the post shows up on other people's blog rolls and when they click on them, it says the page doesn't exist. I did that once and got a few people saying they couldn't find my post. I'll send you the link when it's published!!!

  11. I feel well equipped for a pub quiz!

  12. ooooh pub quiz! I had fun doing one of those with my sister and her housemates in new zealand!

    we got a laugh 'cause the first question was identifying the countries of 8 euro coins... we were the only table in the pub with europeans at it (us two, a brit and a german) and if you factor in I'm a coin collector... easy win! (for that question, our classical music skills -or lack thereof- knocked us out of the final running) lol

  13. That was a really informative post! This idea of Ocean-a-thon is really good..Thanks a lot!


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