where have all the tuna gone?

Here it is the same news in a shorter version:
http://www.ansa.it/ansamed/news/sections/environment/20060524202033931231.html
Really bad news.

O Miles what have you done?!
(joking)

too bad people like tuna so much.. they should make grunts the most popular fish to eat

DeepThought said:

O Miles what have you done?!
(joking)

Click to expand...

hahaha poor Miles shoots a few good fish the rest of us dream about and he cops it from all sides.... (though I know youre joking Michael)

With all due respect to Miles, even he couldnt put a dent in the Tuna population by himself. I blame "Dolphin Safe Tuna", a practice which targets small Tuna, thus wiping out future breeding generations. A practice Greenpeace is DIRECTLY responsible for. After all they stirred up a huge fuss over the dolphin by-catch...

And no, I dont agree with the Dolphin by-catch, but when you shift fishing effort to juvi fish, you will pay the price in the long run.

I was indeed joking.

Shadowkiller said:

but when you shift fishing effort to juvi fish, you will pay the price in the long run.

Click to expand...

And targeting the largest specimens of a specie might be bad as well. If there is a genetic relation to size in that specie it can theoretically reduce the frequency of alleles responsible for large size.
I remember an example of river Salmons somewhere in N.America. Fishermen targeted them for size (by nets I think) for some industry related reason and after some years of fishing pressure which was size driven the average size they caught was smaller.

What do you think about open ocean drifting tuna farms?

The point about size is quite valid, minimum size fishing laws may be responsible for putting selective pressure on a population to be sexually mature at a smaller size. Indeed that is something I'm hoping to examine during my Master of Marine Biology degree research next year. IF I can get the money... :head

But.

A Tuna species that grows to almost 700kg in weight is unlikely to be reduced to a 10kg midget species.. A 10% reduction in max weight would be a major change.

What happened in the past is that purse-seiner would find schools of big-size tuna and corral them with the net. Dolphin and sharks like to swim with big-size tuna schools so they got caught as well. Enter Dolphin safe tuna and the target instead became the smaller-size classes. This was good in one respect because it left the big breeding tuna alone. Well, the long-liners still catch them...

So if we want say 500 tonne a year for our market, it would take x amount of 300kg tuna to fill the quota. But when you start targetting fish that are 20-40kg, you remove many, many more fish to fill that quota. And you remove future breeding populations. Oops....

As for tuna ranching (the term "tuna farming" is a lie as it implies the tuna breed in the cages)...

What happens in Australia is this: A purse-sein net is thrown around a school of small fish, which are then funneled into a farm cage and this is towed back to home port. Bait fish species are netted in huge amounts to feed the caged tuna. Incidentally the feed for Australian tuna farms now comes from the US because our fish schools got smashed into commercial extinction. Because there are so many fish in a small area, they get sick. So the "farmer" (read millionare owner who donates lots of money to political parties so he can keep making millions) has to douse them in anti-biotics. This plume of chemicals, along with the waste from the tuna, and uneaten food then fouls the surrounding water. The end result is a big tuna for the Japanese market, fed on fish that could have been eaten by humans.

I don't like ocean caged fish farming. Or any farms that use wild-caught fish to feed their stock. Its a waste, environmentally devastating and does nothing to address the true issue: feeding the world.

And you know the worst thing: 40% of all fish caught from our oceans goes to make fertiliser. :rcard

Yes, that was in essence the Greenpeace argument ref: Tuna farming, lot's of waste, a few individuals getting very wealthy and happy Japanese sahimi-eaters. Unfortunately for me the Spanish are the worst culprits in the Med. I wonder how easy it would be to freedive the outside of the net, cut a big hole and let all the tuna out

Sounds like great fun, I'm in :t