The rare Antarctic toothfish may be the poster fauna for vanishing marine biodiversity.
At the heart of a dramatic 21-day, 3,900-nautical-mile chase through snowstorms and the rough seas of the Southern Ocean by the Australian navy last year was an endangered maritime species named the Patagonian toothfish. Known on the high seas as "white gold," and in the fish markets of the world as the highly prized Chilean Sea Bass, this fish, along with its identical sister species the Antarctic toothfish, are arguably the poster fauna for vanishing marine biodiversity in the icy waters of the Southern Hemisphere.
Fisheries and customs officials were in pursuit of the Uruguayan-registered vessel, Viarsa. When they finally boarded the ship 2,000 nautical miles from Cape Town in the South Atlantic, they discovered 90 tons of the rare fish worth more than a million dollars. (Toothfish sell for $19 a pound in U.S. grocery stores.) The cache—and the few others that are actually discovered—illustrates the wild card in the already stressed fishing stocks of the world. The United Nations Food and Agriculture Organization's fisheries department estimates that 75 percent of the planet's "major fisheries are fully exploited, overexploited, or depleted."
Arthur DeVries, an LAS biology professor, has been traveling to Antarctica since 1961: 41 research trips in all. Over those four decades he has seen the world's fishing fleets turn their attention to the south, where fishing was historically minimal. A multinational group called the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) oversees the majority of the waters surrounding the Antarctic continent for conservation. Information on genetics, life spans, spawning areas, and migration patterns is nonexistent to scant. "Much of the fishing ground for this toothfish is within the commission's conservation area, but there are a lot of pirate ships that go down there and fish it illegally," DeVries says. "That makes it very difficult to regulate the fishery and nobody knows for sure what sustainable yields would be."
The missing science is key to CCAMLR's efforts to effectively manage the more than 270 species of fish in the area. DeVries has already contributed key pieces of this much-needed science, but many unknowns exist.
"One of the questions regarding the Antarctic toothfish is we don't know where it spawns. They speculate that it spawns out somewhere north near the Antarctic Front and that its eggs are pelagic [deposited in open waters]. One of things we don't know is if it spawns every year or every other year. It's possible that it may be every other year in which case their reproductive potential is not all that great."
He also noted with concern that annual harvests of Patagonian toothfish were declining. What further concerned DeVries was the recapture from a fishing vessel some 62 miles north in the Ross Sea of an individual Antarctic toothfish he had personally tagged four years earlier. Toothfish can attain weights of more than 200 pounds and can live up to 50 years. By measuring the annual translucent zones—a type of aquatic growth ring—present in the otolith—a piece of calcium carbonate found in a fish's inner ear—Devries confirmed just how slowly the toothfish grows.
This method of dating the fish had long been assumed, but it wasn't until DeVries and two New Zealand scientists tested 31 otoliths from Antarctic toothfish caught in 2001 that the thesis was conclusively confirmed. This scientific method of measuring growth rates in toothfish could prove to be a valuable management tool in determining size and catch limits.
"The growth rate is not very substantial—about 2.5 centimeters a year and a weight gain of one kilogram. They appear to become sexually mature at about eight or nine years.
"Someday they will start commercially fishing in that area and I thought they would want to know something about the growth rate."
Vessels often catch toothfish that haven't had the time to enter the reproductive phase of their life cycles. The unforgiving fishing technique of long lining, coupled with the equally harsh temperatures, makes tossing back an immature fish impossible. DeVries, who in 1964 discovered the antifreeze molecule that keeps fish alive in the freezing Antarctic waters, notes that the toothfish, which lives in minus 2 degrees Celsius seawater, dies as soon as it is exposed to the average minus 5 degree Celsius polar air. Knowing this simple fact has the potential to alter the way fish are harvested in the Earth's coldest and windiest continent.
But many seminal pieces of research regarding the toothfish are still missing, including demographics, life history, and genetics. The last item is especially key in determining how much sustained fishing the species can sustain. With that in mind, DeVries turned to LAS professor and head of the Department of Animal Biology Ken Paige, and graduate student Robert Parker (MS '02), in a collaborative research project to investigate the patterns of genetic diversity between random populations of Antarctic toothfish. DeVries supplied 42 samples of the Antarctic toothfish—21 each from two areas 3,000 miles apart in waters near McMurdo Sound and Brabant Island—to Paige's laboratory. Paige and Parker then extracted DNA from heart and muscle tissues to assess genetic diversity. The results of the study, published in the journal Polar Biology, were not promising with respect to widescale harvesting of toothfish.
"We found that toothfish populations are likely small given the high degree of genetic similarity," Paige explains, "They have such little diversity even among populations despite being distinct.
"In other words, they aren't mixing and haven't mixed for maybe hundreds of thousands of years based on the genetic structure. "
With each generation, inbred populations that lack genetic diversity produce fewer and fewer offspring. A slow-maturing, easily caught species such as the toothfish will have a difficult time withstanding the pressures of commercial harvests. Extinction is a possibility.
Paige says even though this is technically a "pilot study," alarms should go off among conservation groups. "We can cause a spiraling down of reproduction. To lose the genetic diversity will leave them less capability to adapt to any changes that might occur, whether it be fishing pressures or global climate changes."
Exploratory fishing began a few years ago in the CCAMLR conservation area. This year 13 boats have permits to catch and sell the Antarctic toothfish. Paige and DeVries hope their research paper, which cautions against large amounts of commercial fishing, will be used in future management decisions.
"This is a study that really does have applied importance to fisheries management," Paige remarks. "It says, ‘Let's be careful. Let's not overfish.' We're already over fishing marine systems. Let's not make the same mistake in Antarctic waters as well."
By Stephen J. Lyons, July 2004