The Why Files The Why Files --

New study asks: How many fish in the sea?
POSTED 28 MAY 2009
Red porgy, catch per unit of effort
 From 1982 to 1984, 7 fish were caught per hour, from 1997 to 1999 less than one per hour
Records for salt waters, Southeastern United States NOAA
Research surveys show that most species of reef fish are declining.

An ocean of questions

More than two-thirds of the planet is covered by ocean, and scientists don't have a firm grip on what lives in all that salt water. A great number of mysterious critters live at great depth, but near the surface, fish and whales have been disappearing at an alarming rate.

Fish provide 15 percent of our total animal protein, yet in 2007, the United Nations described 17 percent of the world's fish stocks as "overexploited" and 7 percent as "depleted." In the Southeast Atlantic, the Southeast Pacific and the Northeast Atlantic, the U.N. said, the "proportion of stocks falling into the overexploited, depleted or recovering category runs from 46 to 66 percent of the total."

By nature, most assessments of marine life are fragmented, but in 2010, a decade-long project called the Census of Marine Life will report the big picture: What plants and animals live in Earth's liquid cloak?

Solving the mystery of history

One component of the Census, called the History of Marine Animals Project (HMAP), is exploring how populations of fish, birds, turtles and marine mammals have changed since humans began catching them more efficiently. The data will show what a non-scientist would call a "normal population" for these ocean animals.

One of the earliest depictions of trawling,
from 5th century Tunisia

The charcoal shows four people in a canoe. Two of them pull on both of the net's ropes
Trawling - dragging a net through the water - was an early and productive fishing practice.

At the Oceans Past meeting last weekend in seaside Vancouver, British Columbia, HMAP researchers discussed what they have learned from the worldwide effort to describe ocean animal populations. If you've read The Why Files -- or bought fish lately -- you know fish are getting rare and dear. Fishery experts have been caterwauling for a decade or two that overfishing, coastal pollution, habitat disturbance and damming of rivers are slashing the number of many marine animals.

The history project confirmed that important, desirable, tasty fish are growing scarcer. Harder to catch. Smaller. "The basic finding is that in nearshore areas, we have lost between 85 and 90 percent of the biomass of all the big fish," says Poul Holm of Trinity College Dublin, the history project's chair.

A group is painted hauling in a net next to a pier.  A monastery can be seen across the bay
Nevsky Monastery, 1815 engraving by I.A. Ivanov.
Monasteries in Russia provided essential records of fishing activity from past centuries. Notice the net being hauled in at bottom left?

Past: Key to the future?

The elite group of disappearing fish includes the top, tasty carnivores, such as salmon, cod, tuna and swordfish. In many cases, the mid-ocean populations may be larger, but data on them also tends to be less reliable. In any case, the general trend is to fish out coastal areas, then move further offshore and repeat the process.

"We have seen a global depletion of resources in the ocean and in some sense the ocean ecosystem," says Andrew Rosenberg, chair of U.S. committee for the Census of Marine Life. However, Rosenberg, a professor at the University of New Hampshire and former deputy director of the U.S. National Marine Fishery Service, says that in some places, "there have been extensive efforts to rebuild, recover some of those resources."

Rosenberg contends that history has an essential role in both fishing regulations and efforts to restore ocean productivity. "We need to be guided by a deeper understanding of what is possible, and we can only understand what is possible if we look at history, and not just at what exists now. We often think what we observe in our lifetime, or our parent's lifetime, is the good old days, but that may not be true, because the natural world proceeds at its own pace, not at our pace."

The history project is like no other, says Holm. "It's certainly safe to say no similar project has been undertaken for ocean history, and it's probably one of largest environmental-history projects ever." In a dozen locations around the world, for the past nine years, about 100 HMAP researchers have been scrounging through records, seeking to document who was catching how much of what:

A study of the seas of northwestern Russia used monastery records to document catches of Atlantic salmon, cod, walrus and herring.

Researchers in Indonesia used a combination of interviews and documentary research to explore the role of shark fishing in the local culture and economy.

In Southeast Australia, where trawling (dragging a net through the water) began in 1915, scientists used old log books to assess the pre-trawling populations; their results have given fishing regulators a better picture of baseline conditions.

In Newfoundland and the Grand Banks, where the once-abundant cod fishery has collapsed, researchers have scoured archeological sites for cod bones dating back as far as 1675. The bones show the size and age structure of cod before industrial fishing started to make a dent in cod stocks.

Map shows seas of northwestern Russia, Indonesia, Southeast Australia, Newfoundland and the Grand Banks
Map from HMAP
The History of Marine Animal Populations had teams working in the green regions.
Over time the average fish in the pictures shrunk from over 100 centimeters to about 30 Over time the average fish in the pictures shrunk from over 100 centimeters to about 30
Photos: Loren McClenachan, Scripps Institution of Oceanography, Monroe County Library
Photos from Key West, Fla., show an 88 percent decline in weight of trophy fish, most likely due to overfishing.

The study has confirmed conventional wisdom -- although that wisdom was not always accepted by fishing regulators. "For ages there was anecdotal evidence that fishes used to be much larger," Holm says. "But most people said, ‘Okay, they are just telling a tall story.' But when we look into the data, we find that yes, in fact, fish tended to be much larger."

But are these old numbers reliable?


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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