Human ‘Signature’ in Fish Losses

Some whaling nations have charged that whales are eating more than their fair share of prized fish species. In fact, it’s we humans that are overeating this finned fare, reports Daniel Pauly of the University of British Columbia. He released a new analysis of data about pressures on fish stocks around the world yesterday in Santiago, Chile. It was the opening day and venue of the International Whaling Commission’s annual meeting.

Pauly’s report has been filed (if inadvertently buried) on the website of Humane Society International, the advocacy group that commissioned it. When I finally stumbled onto the report, it was too late to glean any pearls for my posting yesterday. That blog had been prompted by an HSI teleconference late yesterday on the new report, during which I took the opportunity to speak briefly with Pauly.

The whales-ate-my-fish argument makes marine mammals a “scapegoat for the current overexploitation of the world’s marine resources by humans,” according to his new report. Indeed, although much of the global fish harvest comes from waters off of developing nations, fish consumption tends to be highest in distant countries, typically wealthy industrialized nations.

Pauly and coauthor Wilf Swartz attribute the charge of whale gluttony to a pair of Japanese papers — ones never subjected to peer review — that attempt to calculate the tonnage of marine protein downed by these animals.

The Asian teams took what they estimated to be the number of whales in existence and their relative sizes, then calculated the daily calorie intake needed to sustain this mass. They multiplied the resulting figure by 365. This sum — between 300 million and 500 million metric tons a year — was described as some three to six times more fish than is eaten by people. So, the Japanese papers concluded, knocking off some whales should leave more fish to sate human appetites.

While acknowledging that such calculations may sound reasonable, Pauly and Swartz maintain that they’re not grounded in science.

First, the UBC pair note that the number of whales remains uncertain, as is the size of their appetites. Moreover, these animals tend to have highly specialized diets and feeding grounds — neither of which overlap much with humans. Pauly and Swartz cite one global analysis of marine-mammal diets that found only about one percent of the dining by marine mammals, including whales, competes with fisheries targeted by people. (It would have been nice, by the way, had a speaker at yesterday’s teleconference bothered to mention such data.)

What we prefer to eat are tuna, salmon, cod, sea bass, flounder — even, in some regions, sharks. And when commercial fleets target such fish, they almost invariably hunt the biggest species first. And they’ll preferentially go after the biggest animals within each species. As these big fish, usually the top predators, begin to disappear, smaller and bonier fish begin to dominate. As fleets start focusing on them, these species can crash, leaving even smaller or less desirable species. The mass of animal protein in the seas may stay much the same. But the dominant creatures that supply that protein may change dramatically — from, say, a balanced mix of sharks, groupers, and herrings to a distorted web taken over by jellyfish, eels, and sea cucumbers.

This fishing down the food chain — from big animals to small ones — is the “signature” of human predation, Pauly says. And that’s what’s showing up in fisheries around the world. By contrast, he notes, fish tend to eat the tiny animals first and eventually move up the food chain. Indeed, most of the cetaceans that IWC members have been complaining about as compromising human fish supplies are filter-feeding whales, Pauly said yesterday. They primarily eat tiny shrimplike animals known as krill — hardly the species we prize for dinner.

But even whales that dine on fish don’t usually target what we want. Pauly and Swartz say these behemoths choose instead deep-water squid and other deep animals, such as tiny lantern fish. In fact, the scientists point out, the chemical makeup of those fish render them “unfit for human consumption even if their size, appearance and consistency allowed for it.” (This is another point no one bothered to mention at yesterday’s teleconference.)

Finally, most whales don’t eat even krill when they’re visiting coastlines of the nations complaining most about the animals’ whale of an appetite. They’re just courting and mating, during this period, Pauly maintains — not dining.

The real pressure on marine fisheries today is the unsustainable harvests by commercial fleets, the new report charges. Much of this industry is aided by subsidies that hide the real costs of overexploiting marine resources. Pauly and Swartz suggest that those subsidies might effectively be fought through the World Trade Organization using science to demonstrate their ecologically destabilizing impacts. (Hint to HSI: Fleshing out the magnitude and ecological toll of such subsidies would have made this argument more compelling.)

The UBC pair also argue for greater development of marine reserves. These no-take zones prohibit not only fishing but also other environmentally destructive human activities.

Concern over declining fish stocks has developed because “we have treated the ocean like a frontier,” says Elliott Norse, president of the Marine Conservation Biology Institute, in Redmond, Wash. “In a frontier, people behave as if nobody else is there. So, I can take what I want, kill what I want, throw wastes where I want.” And that was acceptable where only a few individuals were involved, such that their impacts were negligible.

As humanity’s footprint on Earth’s resource base has grown, this Wild West attitude has become untenable. “We must be respectful of our neighbors — even civilized,” Norse says — and that includes not only toward other nations but also toward neighboring ecosystems.

We’ll see. I like Norse’s ideas but also suspect that those with the clout to impose change are not yet willing to reform their resource gluttony. So our marine environment may get a lot browner before global marine policies really begin to green.

Janet Raloff

Janet Raloff is the Editor, Digital of Science News Explores, a daily online magazine for middle school students. She started at Science News in 1977 as the environment and policy writer, specializing in toxicology. To her never-ending surprise, her daughter became a toxicologist.

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