The Why Files The Why Files --

New study asks: How many fish in the sea?
POSTED 28 MAY 2009

Telling a fish story

An underwater metal grate with large openings lets fish, but not the green sea turtle, enter the net
Photo: NOAA
A loggerhead turtle escapes a net through a turtle excluder device, which reduces one destructive form of "by-catch" (the trapping of non-target species).

The History of Marine Animals Project has compiled an impressive set of data on past animal populations, but do their depressing numbers accurately describe the real world? After all, everybody loves, but nobody trusts, a fish story...

Although people in the fishing industry refrain from bragging, which attracts competition, they do have an incentive to over-report their catches to regulators, says marine ecologist Heike Lotze of Dalhousie University, who points out that when regulators get worried about fish populations, they may restrict catches.

However, she adds that “there are some good studies on how some countries do over-report catches, thereby masking declines and painting a picture of ‘everything is ok.’ On the other hand, many vessels fish over their quotas and there are a lot of illegal, unreported and underreported catches, which make it really hard to know how bad the situation really is.

And in any case, the old records from logbooks, newspapers, and customs houses do not meet 21st century standards for scientific data, so how can they be considered reliable?

These are legitimate questions, admits Andrew Rosenberg, a member of HMAP at the University of New Hampshire. "We certainly need to cross-check, so we are not relying on just one data series. We want to build our analysis using different sources of information."

Ironically, HMAP chief Poul Holm says the old data "are often much more reliable than modern data. There was no incentive to misreport, which is a huge problem today." Most of the historic data, he points out, was "collected by fishermen for their own use. Overall we are very confident that this is much better than what most biologists use" to study fish abundance today.

Declines around 90 percent in fish populations in North and South Atlantic, Gulf of Thailand and Australia
Data from "Historical baselines..." in the bibliography). Satellite photos from NASA.
Declines in major fish species during the last 40-50 years. Click image for larger map.

Dangerous decline

Holm says the history project has documented massive declines in fish, especially near the shore. "Top commercial species have been fished out and the productivity declines are very much greater than what anyone would have guessed before we began."

Plenty of people remember some "good old days" when fish were larger and more plentiful, but supplanting a systematic approach for an anecdotal one reveals that even those days were not great. "Most fish management is based on data from 20 to 30 years ago," Holm says, but in many areas, fishing had already taken a huge toll, and in fact, the declines predate the introduction of advanced technologies like sonar and global positioning systems.

"If you look at much longer time spans," Holm says, "you are seeing the impact not only of the latest technology, but also of technologies that we had deemed traditional."

Holm cites two destructive technologies that have been around for decades -- the longline that dangles hundreds of hooks from one long line, and drift nets that float near the surface. "Most people probably suspected they were less harmful than more modern technologies, but early technologies can have a quite dramatic impact," Holm says.

Holm says HMAP shows that once large-scale fishing begins, the pattern of decline tends to follow a typical course. "It's happened at different times around the globe. In the Atlantic, 200 to 300 years ago, we took out the top predators, targeted the commercially most valuable fish first." By the late 19th century, when much of the fishing fleet was still powered by sail, "we were looking at quite a developed fishery, with quite high sustained levels of fishing effort."

People line up at a banquet along long tables where fried fish are served from silver warming bins.
For many people, their biggest concern about fish is taste. So how have we adjusted to declining fish populations at the market and dinner table?

Raw Deal

In 2007, the Congressional Research Service reported that 37 percent of fish examined by the U.S. National Marine Fisheries Service were mislabeled. The ever-popular sushi fish, red snapper, was labeled tilapia or another cheap substitute an astounding 80 percent of the time. When overfishing makes popular fish unaffordable, do some in the fishing industry drown their scruples?

Traditional fish fry fizzles

In the Great Lakes, yellow perch may have been declining due to overfishing before the 1970s when reliable sampling first began. Then a 90 percent plunge in population in the 1980s to the early 1990s devastated local fisheries and sportsmen alike. A prevailing theory says this fish fry favorite has flopped because invading zebra mussels steal food from perch larva. Haddock and cod from the ocean have largely replaced perch on the platter.

Chicken of the sea running scared

It's hard to believe, but in 2002, tuna, the longtime heavyweight of the seafood industry, relinquished to shrimp the title of most-eaten seafood. Last year European nations closed their tuna season early and 13 tuna eating nations met in Japan to take the first steps towards tighter worldwide regulations. For producers, jumping ship on wild tuna in favor of farm-raised shrimp is one way to wriggle free of the regulatory tangles.

Almost unanimous

In a study for the marine history project, Heike Lotze of Dalhousie University examined 256 records (some dating back to the Roman empire), and found that the population declines among large fish, turtles and marine mammals ranged from 11 percent to 100 percent, and averaged 89 percent (see #1 in the bibliography).

In one section, Lotze reported on what archeologists have learned about marine animals:

In the southern Baltic Sea, European sturgeon represented 70 percent of the total catch between the 7th and 9th centuries, but just 10 percent of the catch by the 13th century. This sturgeon is now extinct in the area.

Around San Francisco Bay, the white sturgeon became increasingly scarce from 2600 to 700 years ago, and was replaced by smaller species.

In New Zealand, the fur seal disappeared from 90 percent of its range by 1800, 400 years after the Maoris started hunting them.

Lotze found other declines in marine animals in other types of data:

After whaling began around 1000 AD, the North Atlantic right whale was nearly exterminated. About 300 survive today.

Data from nesting beaches shows that the green and hawksbill turtles have suffered a 99.7 percent decline in the Caribbean.

The tonnage of cod living in the once-productive Grand Banks (southeast of Newfoundland, Canada) has plunged by 97 percent since the 1850s.

Recovery: Hearing from herring...

If you're sunk in an empty-ocean bummer by now, you're not alone. Friends of the fish fry and animals alike have been concerned about life in the ocean for years. And just because HMAP tells us that 27,000 southern right whales swam between Australia and New Zealand 200 years ago, nothing guarantees their return. Ditto for cod, once a dominant fish in the North Atlantic that fed North America and Europe for centuries.

"It's one of our concerns, that this could easily turn into a doomy-gloomy story," says Holm, overall director of HMAP. "It's true that a lot of what we are looking into is quite depressing, but on the other hand, we do see glimmers of hope, we have good evidence that fishery management works if you allow it."

The largest "experiment" in fish management, he says, was World War II. The industrial countries on both sides forewent fishing in favor of fighting, and "Fish stocks rebuilt, and the ecosystems were much healthier." Regulations, Holm adds, can have a similar, if less drastic, effect.

One example comes from the North Sea herring, which was "fished down to a level where it could have gone extinct," Holm says. In 1976, the European Union introduced a moratorium on herring fishing, which "was hugely contentious at the time, gave the European Union a bad name among fishermen, but 10 years later, biologists concluded that fish stocks had rebuilt, and opened fishing on herring."

Studies show the value of regulating fishing and setting aside marine reserves, Holm says. "It takes time and needs a concerted effort but if you do it, it does work."

Wreaking recovery, or wrecking recovery?

Marine fishing is a classic "tragedy of the commons" -- a situation where individuals benefit from overusing a common resource, thus causing harm to everybody, including themselves.

This 1675 map shows Newfoundland, New England, New Scot Land, and the Gulf of St. Lawrence
The first English chart of New England waters shows the Grand Banks and Georges Banks, both fishing hotspots for several centuries, and both showing major fish declines.

A prime tragedy of the commons has played out in the Northwest Atlantic, where major cod populations have failed to recover despite government attention in the United States and Canada. "There has been some effort," says Andrew Rosenberg, who used to work with the U.S. National Marine Fisheries Service. "We have written recovery plans for cod, but in many cases, we never got the exploitation rate down to the level that was expected to allow recovery." Cod in U.S. waters may be edging toward recovery due to a total fishing ban on George's Bank, but although "we have gotten the fishing rate down, we never ended over-fishing on cod stocks" in Canada, Rosenberg says.

For this reason, Rosenberg concludes, it's unrealistic "to be shocked that there is not [cod] recovery. Fish don't read the management plans, they only respond to how many of them we kill."

It's not possible to know whether HMAP will make a difference in the contentious realm of fish regulation, Holm says, but it should help in some cases. "There is a world of difference between people who are impoverished, like the Hong Kong fisherman who is involved in piratical deep sea fishing for fish that have a high market value in western restaurants, who probably have little sense of history or of the need for conservation. But in many local communities, there is concern, because it's within living memory that things have changed. Once people realize that the changes are not just their own anecdotal picture, but that they actually fit into a larger picture of loss, that becomes a motivating force that can change minds."

Historical evidence is "neutral ground," Holm concludes. "It's not about how we manage today, it's about what was there before. This opens a new dialog based on the memory, the records, of the fishing people themselves. It's not something they can run away from."

Fish around in our bibliography.


Terry Devitt, editor; Nathan Hebert, project assistant; S.V. Medaris, designer/illustrator; David Tenenbaum, feature writer; Amy Toburen, content development executive

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