The Uncertain Life Of A Squid
Posted 22 April 2005 - 11:35 AM
[This is the print version of story http://www.abc.net.a...es/s1342803.htm]
Robyn Williams: Let's take a look at what happens when the fish go: the squid explode. George Jackson is at the Institute of Antarctic and Southern Ocean studies in Hobart.
George Jackson: Well, they’re probably increasing in numbers in the ocean because of over-fishing from their competitors and their predators the fin fish, and as a result of that you remove the competitors, remove their predators and you end up with more squid in the ocean.
Robyn Williams: Is that a good thing?
George Jackson: It is if you’re a squid, I guess. I mean, it’s obviously changing the balance of things, a lot of areas say, the Gulf of Thailand for instance; a long time ago a lot of the big fish have been removed and they are now catching squid in the Gulf of Thailand because they grow so fast, they’re like weeds, they’re filling that niche when the fish have been removed.
Robyn Williams: I did an interview with Daniel Pauly from Vancouver and suggesting and Sylvia Earle has backed this up, that 90% of the big fish of the oceans have been removed in the last what 20 to 50 years. That’s astonishing, isn’t it?
George Jackson: Yes, that was published recently in Nature and that’s what they’re saying now. So that being the case, if you remove 90% of your predators it suggests that there’s probably a lot more squid than perhaps, maybe there ever was, I’m not sure.
Robyn Williams: Who eats squid – which fish?
George Jackson: Oh, any of those large predatory fish; the tunas, the bill fishes, depending what environment you’re on. If you’re on a reef there’s the large cods and so forth, the reef fish, any large predatory fish will be eating squids, as well as marine mammals and birds particularly in the Southern Ocean.
Robyn Williams: So I suppose if we’re to leave them alone - that is the fish - they could bounce back because there’s so much food around.
George Jackson: Yeah, I mean if you stopped fishing sure, eventually populations will build up and they’ll balance themselves out, but a lot of areas have been so denuded that squids other cephalopods are increasing in numbers.
Robyn Williams: And what do the squids themselves eat, because surely their own population will be limited by what is around for them to feast on?
George Jackson: Yeah, they tend to eat fish and other squids and crustaceans. The bigger ones predominately eat other squids and fish, they’re highly cannibalistic so they just eat each other there’s nothing else to eat. But in a lot of these environments that have been over-fished there’s lots of smaller fish around that are fine for the squids to feed on, and other smaller crustaceans and things. So there’s still food around in the water column.
Robyn Williams: Are they selective when they’re eating each other, are they going for different species of squid or if you’re around they’ll eat you?
George Jackson: Yes that’s right, particularly if you’re smaller. They’ll eat the smaller ones, so you get schools of squids with not many little ones in it, or these squids that migrate vast distances they just eat each other along the way to fuel the migration. It’s all because squid grow so quickly, they don’t store fats or lipids, they have a protein-based metabolism so everything is channelled into growth, and that’s why they live such short life spans and grow so rapidly: everything’s just eaten and turned into growth or reproduction.
Robyn Williams: That sounds horrible, I mean squid society must be a ghastly place.
George Jackson: Well, it all happens fast, it’s life in the fast line: they live fast and die young and that’s just how their life cycles are tuned to the environment.
Robyn Williams: And they move fast as well, don’t they?
George Jackson: Yes, they have jet propulsion, it’s not a terribly efficient way to move but it does work for them, and they also have fins and they can beat their fins and they swim backwards. So some of these larger ones that undergo large migrations they can cover thousands of kilometres.
Robyn Williams: Are the shoals huge?
George Jackson: If you talking about squids off California they are huge schools of squid but off the east coast of North America, off South America there are big, well commercially fished species that do take large scale migrations between Nova Scotia and Florida for instance on the east coast of North America.
Robyn Williams: And what about around here, around Tasmania?
George Jackson: OK we’ve got the inshore southern calamari, a very large species that can grow to several kilos, it lays eggs in very shallow water, just a few metres of water. Then we’ve got the arrow squid and there’s a fishery for the arrow squid in southern Australian waters, it’s a Commonwealth fishery. They’re large muscular squid, big numbers of those - we don’t have real good estimates on just how many are out there but there are good size populations.
Robyn Williams: And how do you study them, do you go out into the waters and watch or do you bring them into the university here and put them in tanks?
George Jackson: Most of mine come in frozen fish boxes in plastic bags. It’s been great, the local fishery for instance, from the deep water fishery I get all sorts of weird and wonderful deep water squids from here. From the aero squid fishery we’ve gotten samples through different ports and they are simply frozen and we do our age, growth and reproductive studies on them.
Robyn Williams: And they don’t get much older than say, what 200 days, not even a year or two?
George Jackson: OK, for tropical squids - I’ve done a lot of research on tropical species off northern Australia into Thailand and so forth, I haven’t found any squid older than 200days. Southern cooler ones appear to be about a year old. We know that because we have techniques so we can age them. They have these little statoliths or balance organs in the back of their head and we can section those and look under a microscope and have daily rings just like tree rings in a tree stump. You can count these rings and they’ll tell you their birthday, and how old they are, and how fast they grew. They’re little calendars they carry round in the back of their head, which has really unlocked their life history for us to understand.
Robyn Williams: Amazing creatures but why are you concerned about aspects of global warming in association with these creatures?
George Jackson: Because, as I mentioned, they have this fast growth, short life histories, they move in like weeds and they can fill vacuums. They also grow incredibly faster if you just warm them up a little bit, so if you raise the temperature a degree you’ll end up with a squid growing much fast and it starts to snowball, so it’ll get much bigger earlier in life. So I suggest that for shallow water, say warm water species, if global warming begins to warm the environment up we quite likely will end up with many species of squids that will be completing their life cycles much quicker, reproducing earlier and perhaps their populations will increase.
Robyn Williams: Is there evidence along those lines yet?
George Jackson: No. We have evidence, experimental evidence that you can raise the temperature and the squid will grow much quicker. So we know then, if the environment will increase somewhat in temperature we know that the squids in that environment will be growing faster; that means they’re going reproducing sooner and there could be somewhat of a population explosion. But the possibility exists that global warming could favour squid.
Guests on this program:
Institute for Antarctic & Southern Ocean Studies
University of Tasmania
Presenter: Robyn Williams
Producer: Polly Rickard and David Fisher
Posted 22 April 2005 - 11:44 AM
Thanks for posting this Glen
Posted 22 April 2005 - 02:21 PM
Well, i guess that means...more squid on the dinner table for us !!
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