Off the coast of Kodiak Island, in the heart of the Gulf of Alaska, this is the sea of plenty. For hundreds of years, Alaskan fishermen have set nets in these waters, considered one of the richest marine ecosystems on the planet. For third-generation fishermen Hunter Berns and his young crew, today the salmon run looks promising.

HUNTER BERNS: Right now we're probably gonna pull in about 1,000 fish tonight, but, you know, on average we get about 200 to 300 fish a day, sometimes less and obviously sometimes more. It just really depends on the wind, the time of the season.

But even here, despite such apparent abundance, all is not well. Thousands of big predators in western Alaskan waters have vanished in the past 50 years, most notably, the largest sea lion of its type, the Stellar sea lion.

KEN STUMP: The Stellar sea lion has declined approximately 80% across the entire range from Prince William Sound to the western Aleutian Islands. In some areas it's much higher than that even, a greater-than-90% decline.

Ken Stump has been a leading force behind the charge to protect what remains of Alaska's Stellar sea lion stock.

KEN STUMP: Stellar sea lion population in the '60s were, within this region, were approximately 200,000, 250,000 animals, today we're looking at 20,000 to 30,000 Stellar sea lions in the same area and, you know, in less than 40 years that many animals have vanished.

He believes there is one key reason behind the sea lion decline. Commercial fishing's removal each year of 2 million metric tons of fish - potential food for the sea lions - has caused a fundamental shift in the marine ecosystem. And he maintains the only way to bring sea lions back is for fishermen to take less.

KEN STUMP: To say to fishermen that we need to remove fewer fish from the ocean is the most unpopular thing that anyone could say. It is something that I think we all find hard to say because we know it is politically unpalatable. But I think it's a hard truth.

Three years ago this issue came to a head, with several groups suing the National Marine Fisheries Service, the agency responsible for regulating fishermen and protecting endangered species. A federal judge sided with environmentalists, leading to fishing trawlers being banned around key sea lion sites.

KEN STUMP: I have been accused of working to put fishermen out of business and it's simply not true. And as I've noted to some of those fishermen who said to me, no, it is you who are your own worst enemies and have put yourself out of business over and over again, and that's exactly what we want to stop. If we fish less today, if we remove fewer fish, hopefully we will have more fish for, you know, the indefinite future.

In recent months, a raft of reports has confirmed many environmentalists' worst fears - the world's oceans are in crisis. The seas are being emptied. More than 70% of the world's commercial fish stocks are now considered fully exploited, overfished or collapsed. And a growing number of marine species are reaching the point where extinction is considered a real possibility. Jim Balsiger works for the National Marine Fisheries Department. His job is to help manage the competing demands of Alaska's fishing industry, while protecting the resource. Each year fishermen are told how much they can take.

JIM BALSIGER, NATIONAL MARINE FISHERIES SERVICES: The quota was set at 90 million pounds, which is a fairly conservatively set quota.

He maintains that dividing up the ocean to provide for all is a challenge, but it is possible.

JIM BALSIGER: It's not an easy process deciding exactly what to take. Part of our objective, of course, is to provide fish for people to eat and recreational opportunities, but none of the scientific community wants to see them overfished. Probably driving stocks to 10% of the large fishes, of the large sword fishes, to 10% of their original stocks is too much. Some of those are on the way to recovery, others they are working on recovery plans for.

How best to protect the sea lions remains hotly debated, and nowhere more so than Kodiak Island. Home to more than 1,000 fishing vessels, it is the largest and one of the busiest commercial fishing harbours in America. But when the Federal Court came down in favour of the sea lions, the livelihoods of many fishermen were threatened.

KATE WYNNE, MARINE BIOLOGIST: The debate is not whether they're declining or not - they have obviously declined and everyone accepts that the population dropped off drastically in the 1980s - the question is why.

For the past decade, marine biologist Kate Wynne has been investigating the sea lions' decline.

KATE WYNNE: If people know that they're at fault or know that they're doing something wrong and by changing their habits they can improve the state of things for Stellars, they would in a heartbeat but we have just not had enough evidence that prey limitation alone is responsible for the decline. And so, for the fishing industry, it's been a hard pill to swallow, that they need to kerb their fishing to save Stellar sea lions when it hasn't been proven that that will help.

It's not the first time that fishing practices in Alaska's sea of plenty have been brought into question. Dorothy Childers is the executive director at the Alaska Marine Conservation Council.

DOROTHY CHILDERS, EXECUTIVE DIRECTOR, ALASKA MARINE CONSERVATION COUNCIL: Kodiak Island was the king crab capital of the world. And there were immense king crab here in huge abundance and they called it the pots of gold because they were so valuable and the fishermen just flocked here from everywhere to catch the valuable king crab and it collapsed, utterly, completely collapsed in the early '80s.

REPORTER: Why?

DOROTHY CHILDERS: It was a combination of overfishing on a declining population and some combination probably of oceanographic factors. It just was pushed down by the fishery to such a low degree that it's not shown any signs of recovery.

Kodiak's history of boom and bust cycles is a result of never-ending demand. But in the face of dwindling stocks, the world's appetite appears far from sated. Alaska is home to some of the largest and most complex fish processing plants in the world. Here, nothing goes to waste. Virtually every ounce of the fish is used - fillets are flash frozen, those too small to fillet are churned into paste and any waste is ground into fish food. Recent studies estimate that stocks of many fish are now a tenth of what they were 50 years ago, before the onset of commercial fishing. As prized species have diminished, fishing fleets have moved down the food chain for smaller fish. The scientific world cannot keep pace.

DOROTHY CHILDERS: We just are starting to understand what we have lost, with the study being one of the first to demonstrate that, you know, research has yet to discover what that really means.

In the icy waters of the North Pacific, this fish, the halibut, is closely monitored. Across the fishing industry, its management is being hailed as a rare success story. This trawler has just come back from a week-long research expedition.

RAY BYRNE, HALIBUT RESEARCHER: We measure every fish that comes on board, we assess the sexual maturity of the legal-sized fish. This gives us some idea of the amount of fish that are available to spawn in the upcoming season.

North America's halibut fishery is protected under an international agreement. For the past 80 years, harvest limits have been placed on the amount allowed taken in these waters of this unmistakable fish.

RAY BYRNE: They start off with an eye on each side of the head and, as they evolve and mature, one eye migrates to the other side of the head so that they are both on the same side.

In waters across the world, 90% of the ocean's large fish - such as halibut, cod, tuna and marlin - have been fished out since large scale industrialised fishing began. In Alaska, halibut continues to thrive, but no longer in size.

RAY BYRNE: This fish is over 2m long and you won't see very many that are a whole lot bigger and maybe, two or three fish during a trip will be that size.

In these managed waters, harvest limits are tied to quotas allocated to individual fishermen.

CHUCK LEWIS JR: This is unusually warm and sunny and calm. It's pretty nice.

Chuck Lewis runs one of the smallest halibut fishing operations out of Kodiak. It's a one-man operation.

CHUCK LEWIS JR: Since I'm always alone I've got a habit of having this thing on me, you know, so I don't fall overboard. That's the worse thing that could happen to you.

He's been fishing these waters off Kodiak for more than 30 years.

REPORTER: So Chuck, how many hooks are you putting down?

CHUCK LEWIS JR: Today?

REPORTER: Yeah.

CHUCK LEWIS JR: 300.

REPORTER: Is that about what you do on an average day?

CHUCK LEWIS JR: Yeah, that's - you know, a lot of boats will do 3,000. But my little operation don't do much. That's average, yeah.

REPORTER: How many fish do you pull up off those 300 generally?

CHUCK LEWIS JR: Oh, on an average, 20. Maybe - yeah, that's about average.

The market's demand for halibut is growing.

CHUCK LEWIS JR: I would say it's something that the American people like because of the lack of bones for the most part and it's kind of white and clean and pretty and doesn't really taste fishy.

For fishermen like Chuck, holding allocated quota is money in the bank. Weather and price determines when he goes out.

CHUCK LEWIS JR: I've got so many thousand pounds I'm allowed, it's about 8.5 months to 9 months to catch 'em, and if the price is low I just don't go.

Halibut may be facing commercial extinction elsewhere, but in North American waters around here, a record harvest allocation has been set. Chuck is concerned the target and the level of optimism may be too high.

CHUCK LEWIS JR: We set out skates, what we call 100 hook set, and during the '70s we used to get about 50 pounds, early '70s. By mid-'80s we were getting 1,000 pounds. Now its down to about 300. But that's pretty good, that's pretty good. But the Government needs to be aware that - to be conservative about it and that's the best approach.

But it's the fate of the salmon industry which is the immediate concern of most Alaskans. Right now, salmon are on the run in record numbers. 50 years ago, Alaska's salmon industry was almost wiped out. With the help of science, salmon stocks have been bolstered.

DONN TRACEY, BIOLOGIST, ALASKA DEPARTMENT OF FISH AND GAME: Those fish are counted as they migrate upriver and that information is used to determine what the - not only what the adult salmon return is during a given year, but also to regulate that return in order to provide for fishing opportunities, harvest opportunities by the user groups and also to provide a spawning population of adult fish that will ideally produce a maximum sustained yield from that particular population.

It's this issue, that of maximum sustainable yield, that has divided environmentalists and fishing authorities. For environmentalists, setting the allowable catch at the maximum is not the best way to sustain the fisheries into the future.

DOROTHY CHILDERS: We have a system called maximum sustainable yield and it's all about maximising how much fish can be removed without pushing different species to some unacceptable threshold. And that's a system that's pretty outdated and I think most scientists would agree that it's not the most precautionary way to manage fish.

Fisheries officials defended maximum sustainable yield because in their view the scientific data is solid.

JIM BALSIGER: Of those species in Alaska that we have aggressive fisheries for, we have good assessments, we have good information about how many there are, how they're recruited, how fast they grow and how many can be taken to sustain those.

But environmentalists like Ken Stump dispute this.

KEN STUMP: Part of the other problem with this whole theory is that we don't know how many fish are out in the ocean and so we make assumptions that we take X amount out and that we'll get X return but we can be terribly and tragically wrong and we've seen that all around the world. This is one of the reasons why you have these tremendous tragedies like the Newfoundland cod fishery where everyone thought it was state-of-the-art managed, sustainable, you know, best management practices and yet they went out in 1992 and there were no adult fish to be found and that fishery has not reopened.

While many of the world's oceans have been stripped bare, Alaska's fishermen are being forced to confront yet another crisis. This time, it's not for lack of fish.

LACEY BURNS: We're having a really good season in terms of, you know, the numbers of salmon that we're catching. So we're pretty happy.

After decades of controls on salmon, the wild stocks are returning in healthy numbers. But in the meantime, large scale salmon farming has taken off elsewhere and now floods the market. Lacey Burns says the price paid has halved in the past few years.

LACEY BURNS: It's 50% of the value, just straight across, 50%.

REPORTER: You have to catch 50% more to make...

LACEY BURNS: We have to catch double, two times. Like 10 years ago, 10,000 pounds of sockeye was $10,000, now we have to catch 20,000 pounds of sockeye to make $10,000.

In these tight-knit fishing communities the fortunes and misfortunes of near neighbours are felt keenly. Virginia Adams and her husband Jonathan Edwards a 13th-generation fishermen, live just up the coast from Lacey Burns. Together the two women have struggled to protect their families' livelihoods while witnessing others falling by the wayside.

VIRGINIA ADAMS: And salmon, we have pretty good numbers on who's left.

LACEY BURNS: Yeah, last in 19 - or in 2002, 60% of the permit holders in Kodiak did not fish, so that we once had about 600 permit holders, total, 600 family businesses. Now less than 250 are still fishing.

REPORTER: Is that simply because the price has dropped?

LACEY BURNS: Completely because of prices.

Now at a time when market demand for seafood is at an all-time high and Alaskan salmon stocks are on the rebound, fishermen here have found themselves priced out of the market. The irony that fish farming took off elsewhere as they were working to regrow their own wild fish stocks is not lost on Alaska's fishermen and women.

VIRGINIA ADAMS: Our fish has sold itself. Up until recently we've never had to really, you know, pump it up anywhere and now we have heavy, heavy competition and we have to differentiate our product and those of us that have been in the industry a long time and, you know, have been, you know, fairly frugal or whatever have no big debt load anymore, are kind of trying to live through this and hoping that we're going to come out the other end with something that's valuable again.

For Lacey, she's fighting for more than economic survival. This, for her and her family, is about a way of life.

LACEY BURNS: I think that we're going to end up here, probably no matter what, coming out here every year because we've always done it, we've done it for 27 years and I think the boys are going to grow into being crew members here and maybe we can save money that way, by just having the family work the site. But no, I don't see us giving it up. Never.

With world fishing in such a crisis, all eyes are on Alaska with its seeming abundance to see if sustainable management is indeed possible. Environmentalists, like Ken Stump, are not optimistic.

KEN STUMP: Well, if Alaska can't get it right, there's not a whole lot of hope. There's not very many other places where you can still catch this much fish. If we can't protect it here, you know, there's not very many places left to go in the world where we can catch fish like this and where there is this abundance, this productivity that hasn't already been exploited, over-exploited.