FAO thinks global wild caught fish will fall 2 percent to 90 million tons this year

This is close to 4 percent below the all-time peak haul of nearly 94 million tons in 1996.

The wild fish catch per person has dropped even more dramatically, from 17 kilograms (37.5 pounds) per person at its height in 1988 to 13 kilograms in 2012—a 37-year low. While wild fish harvests have flattened out during this time, the output from fish farming has soared from 24 million tons in the mid-1990s to a projected 67 million tons in 2012.

Over the last several decades, as demand for fish and shellfish for food, feed, and other products rose dramatically, fishing operations have used increasingly sophisticated technologies—such as on-vessel refrigeration and processing facilities, spotter planes, and GPS satellites. Industrial fishing fleets initially targeted the northern hemisphere's coastal fish stocks, then as stocks were depleted they expanded progressively southward on average close to one degree of latitude annually since 1950.

The fastest expansion was during the 1980s and early 1990s. Thereafter, the only frontiers remaining were the high seas, the hard-to-reach waters near Antarctica and in the Arctic, and the depths of the oceans. The escalating pursuit of fish—now with gross revenue exceeding $80 billion per year—has had heavy ecological consequences, including the alteration of marine food webs via a massive reduction in the populations of larger, longer-lived predatory fish such as tunas, cods, and marlins.

Unselective fishing gear, including longlines and bottom-scraping trawls, kill large numbers of non-target animals like sea turtles, sharks, and corals. As of 2009, some 57 percent of the oceanic fish stocks evaluated by FAO are "fully exploited," with harvest levels at or near what fisheries scientists call maximum sustainable yield (MSY). If we think of a fish stock as a savings account, fishing at MSY is theoretically similar to withdrawing only the accrued interest, avoiding dipping into the principal.

Some 30 percent of stocks are "overexploited"—they have been fished beyond MSY and require strong management intervention in order to rebuild. The share of stocks in this category has tripled since the mid-1970s. A well-known example of this is the Newfoundland cod fishery that collapsed in the early 1990s and has yet to recover. This leaves just 13 percent of oceanic fish stocks in the "non-fully exploited" category, down from 40 percent in 1974. Unfortunately, these remaining stocks tend to have very limited potential for safely increasing the catch. These FAO figures describe 395 fisheries that account for some 70 percent of the global catch.

Included are the small minority that have undergone the time-consuming and expensive process of formal scientific stock assessment, with the remainder being "unassessed" fisheries. There are thousands more unassessed fisheries, however, that are absent from the FAO analysis. In a 2012 Science article, Christopher Costello and colleagues published the first attempt to characterize all of the world's unassessed fisheries. The authors report that 64 percent of them were overexploited as of 2009. The top 10 fished species represent roughly one quarter of the world catch. Nearly all of the stocks of these species are considered fully exploited (most of these fish have more than one geographically distinct stock), including both of the major stocks of Peruvian anchovy, the world's leading wild-caught fish.

Stocks that are overexploited and in need of rebuilding include largehead hairtail—a ribbon-like predator caught mainly by Chinese ships—in its main fishing grounds in the Northwest Pacific. Despite the unsustainable nature of current harvest levels, countries continue to subsidize fishing fleets in ways that encourage even higher catches. Governments around the world spend an estimated $16 billion annually on increasing fleet size and fish-catching ability, including $4 billion for fuel subsidies. Industrial countries spend some $10 billion of that total. More than $2 billion is spent by China , whose 15-million-ton catch is nearly triple that of the next closest country, Indonesia. The world's fisheries reveal a classic case of diminishing returns.

In a 2012 paper published in the journal Fish and Fisheries, scientists found that overall engine power for the world fishing fleet has grown 10-fold since 1950, while the total catch has grown just fivefold. (In Asia , home to 3.2 million of the estimated 4.4 million fishing vessels worldwide, the growth was 25-fold.) In other words, ships now have to use twice as much energy to catch a ton of fish as they did 60 years ago.

Seafood plays a vital role in world food security. Roughly 3 billion people get about 20 percent of their animal protein from fishery products. It is perhaps unsurprising that fish account for half or more of animal protein consumption in small island developing countries, but the same is true for some much more populous countries, such as Bangladesh and Indonesia (home to a combined 400 million people). With the wild catch no longer increasing, aquaculture has emerged as the world's fastest-growing animal protein source, soon to overtake beef in total tonnage.

China , which has raised carp for millennia, produced nearly 37 million tons of farmed fish in 2010, which was 60 percent of the world total. Six of the world's top 10 farmed fish are carp species, either filter feeders or those fed a largely plant-based diet. But a commonly cited drawback of aquaculture is that wild-caught forage fish—smaller plankton consumers that support the higher levels of the food chain—are often turned into fishmeal and oil used to feed farmed predatory fish, such as salmon and shrimp.

In fact, a caught Peruvian anchovy's main fate is to be fed to farmed fish, pigs, and chickens. And while the share of the wild catch fed to farmed fish has declined since the mid-1990s, scientists recently have called for a reduction in fishing pressure on forage fish by as much as half, well below MSY. They note that if poor environmental conditions lead to poor spawning success in a given year, a much lower catch would provide a buffer against collapse and ripples up the food chain. Recent developments in the Peruvian anchovy fishery help illustrate the vulnerability of forage fish: Warm Pacific Ocean waters associated with a mild El Niño were implicated in a 40 percent drop in the fish's population between 2011 and 2012. In response, Peru , which hauls in over 80 percent of the total harvest, cut its allowed catch for the upcoming season by two thirds to its lowest level in 25 years.

The country's top fisheries regulator admitted, "Technically, we should have said the quota is zero."

There is hope for rebuilding the world's fisheries. In several well-studied regional systems, multiple fisheries have bounced back from collapse after adopting a combination of management measures. These include restricting gear types, lowering the total allowable catch, dividing shares of the catch among fishers, and designating marine protected areas (MPAs).

Around coral reefs in Kenya , for example, communities removed beach seine nets and co-managed a network of "no-take" zones. The result was an increase in total fish biomass, size per fish, and fishers' incomes. Worldwide, 8.1 million square kilometers of MPAs have been designated—an area larger than Australia but covering only about 2 percent of the oceans. Well-designed and managed MPAs offering varying levels of protection provide multiple ecological and social benefits, but marine reserves where fishing is excluded entirely are most effective.

A 2010 study of no-take reserves in Australia's Great Barrier Reef showed up to a doubling of fish abundance and size within them, as well as increased fish populations outside reserve boundaries. In June 2012, Australia announced that it would increase its number of reserves of all kinds from 27 to 60, protecting one third of its waters.

At an 1883 international fisheries exhibition, Thomas Huxley, president of the British Royal Society, said, "Probably all the great sea fisheries are inexhaustible; that is to say that nothing we do seriously affects the number of the fish."

This view prevailed well into the twentieth century. Faced now for several decades with evidence to the contrary, the world has made some progress. But securing a future for world fisheries, especially in a time of warming and acidifying seas, means moving much more quickly to put scientific advice into practice.