Given the shocked faces I get when I tell people I ate horse meat in France, imagine what they'd look like if I had (raw) horse meat sushi!
Japan is known around the world for its sushi - if you ask the regular person on the street what Japanese food is, odds on they're going to say sushi. The increasing rarity of high quality tuna has got to be greatly unnerving for the restaurant industry, rather like it would be for Boston to run low on lobster.
This opens a couple of cans of worms. First, there are the environmental ramifications. With the world's population soaring, people packing tighter into cities (after this year, the majority of people will live in cities). With continued advanced in medical technology, people are living longer and healthier than ever before. As we have more mouths to feed, we put even more strain on the environment (can we say carbon emissions and global warming, anyone?). It's only to be expected that we start to stress our current stocks of fish (both by overfishing and through the mercury contamination from power plant waste). The old adage "survival of the fittest" just isn't appropriate anymore. Seriously, with the technological resources at our disposal, can you honestly tell me that cattle in an abattoir have a fighting chance, and would survive if only they were fit to?
Animals (and plants, for that matter) are becoming endangered right and left. It's impossible to know whether their endangerement, or extinction, will go out quietly, or whether there will be a Butterfly Effect). So, as much as I love eating maguro at my local sushi bar, the fact that it's become harder to come by will perhaps have a positive effect - sushi chefs will start to focus on other fish, meat, and vegetables and help to keep the tuna stock in control and not overfished. Sounds like they've had a good start by passing the lows to reduce fishing already.
The other major issue is one of innovation. And this is huge. Malcolm Gladwell gave a fascinating talk on innovation (as pertaining to spaghetti sauce). If you don't recognize his name, he is the author of two of my favorite books - The Tipping Point (ISBN 0316346624) and Blink (ISBN 0316010669).
The fact that tuna is less available will force sushi chefs to seek out new interesting maki. While I'm not totally convinced about raw horse meat or venison rolls, I'd be very interested to try it, because it's so different. The same things all the time create stagnation of creativity. Granted, sushi is an art form and it's often about simple and clean flavors (I think it's just us crazy Americans who create all these wacky rolls like the Red Sox Maki and Matrix maki). But it seems that any chef who doesn't keep up with the times and strive to innovate will often fall by the wayside (see my blog post on the French haute cuisine environment). While people will always enjoy the classics, it is important to keep the menu fresh and new, the make people cock their heads and go "oooh!" Without innovation, we would not have made the huge strides in nearly every field (especially technology) in the past century.
It's refreshing to see a country taking positive measures to protect the resources it uses, rather than just turning a blind eye and saying "the fish will always be there if we will it to be so." I hope that the rest of the world (especially the US) follows their lead to prevent the mass extinction of the vast number of resources we consume (or waste) on a daily basis.