I made some vague response, but I was floundering and didn't really know the answer. Being the geek I am, I thought I'd do some digging.
Turns out that not all tinned tuna is created equal. Find out more after the jump.
Locating wild tuna in the open ocean is really hard. They aren't just spread around evenly like trees in a forest, there are pockets of really high density in super-fast swimming schools and the rest of the ocean is empty.
Fishermen are clever and quickly figured out that tuna and dolphins hang out together. And because dolphins come up for air, they are much easier to spot than tuna. If you find one, chances are you've found the other. So one method of tuna fishing is to follow schools of dolphins, circle the pod with a purse seine net and haul the lot on deck.
Luckily for dolphins, they are charismatic and pretty and when word got out in the 80s and 90s that tinned tuna came with a dolphin price, people were displeased and pushed for a change. Dolphin friendly tuna was the result and pretty much all tuna now claims to be dolphin friendly, although monitoring or auditing processes are still questionable.
In an effort to minimise dolphin bycatch, tuna fisheries moved towards deploying and fishing around things called Fish Aggregating Devices (FADs) which is a fancy name for structures that float in the sea and attract fish, including tuna. Unfortunately, they also attract sharks, rays, other fish and sea turtles which can end up being accidentally caught too. A scientist called Mr Hall, estimated that for every 1 dolphin saved by targeting tuna schools not hanging out with dolphins, 16,000 small tunas, 380 Mahimahi, 190 Wahoo, 1200 Triggerfish, 20 sharks and rays, 1 marlin, and possibly more fish are incidentally caught. This is because fishers moved to this new method of targeting floating debris which attract all kinds of other critters along with tuna.
In tuna fisheries that supply Australia, the most common accidental bycatch are silky and oceanic whitetip sharks, according to the FAO. I can't find figures on turtles, but given how critically endangered sea turtles are, we'd almost be better off turning back the clock and chasing dolphins again.
I realise this is a highly emotive clip, but it does tell a story that applies to Australia's supermarket shelves. Almost all tinned tuna for sale in Australia comes from the Pacific where use of FADs and purse seine nets is very common.
Pretty much all species of tuna in the world are overfished. Luckily, one species - skipjack - is still going pretty well. It is fast growing and short lived, so it is hard to catch too many. A lot of tuna sold in tins in Australia and elsewhere is actually from other overfished species. But some tinned tuna companies are trying to do the right thing.
Greenseas are doing their best to not catch dolphins, to only buy legally caught tuna and to use the sustainable skipjack tuna in their products. I think they should be applauded for their efforts.
Unfortunately they still use purse seine nets, so silky and whitetip sharks are still being caught as well. I think Greenseas could go one step further and buy from fisherman using the pole and line method (just like a heavy version of the rod and line we all know) rather than the much more indiscriminate purse seine net. This would solve the dolphin issue and minimise the catch of sharks, unwanted fish and turtles.
If you spend 2 minutes and paste the following (or use your own words) into an email to Greenseas, I reckon we could make a real difference.
Thank you for your efforts in supporting dolphin friendly fishing practices and using the sustainable skipjack tuna species in your products.
I would tell my friends and strongly support Heinz and Greenseas if you offered a range of tuna caught using the pole and line fishing method to minimise wasteful bycatch from the purse seine nets you are using.
So thanks Jen for getting me thinking about this.
Other sustainable fish options for local readers are calamari, snapper and King George whiting. The DPI have a page on Victorian fisheries trying to do the right thing. Very few food-miles too. And a video...
Greenpeace recently audited canned tuna in Australia.