Deep-sea Disappearing Act

Where the continental shelf drops off into the inky abyss of the northwest Atlantic Ocean, and otherworldly creatures stalk mile-deep canyons, trouble is brewing. Commercial fishing may be wiping out whole populations of deep-sea fish before science has adequately studied them, according to Canadian researchers.

In the waters off Eastern Canada, populations of deep-sea fish have plummeted by up to 98 percent from 1978 to 1994, say scientists from Newfoundland’s Memorial University. The five species experiencing the sharpest declines are the spiny eel, the blue hake, the roundnose and onion-eye grenadiers, and the spinytail skate, which is a flattened cousin of sharks.

The virtual disappearance of whole fish populations is especially alarming because some of these fish and the complex ecosystems to which they belong weren’t even known to science until about 30 years ago.

“It’s a wake-up call,” said Richard Haedrich, lead author of the study, which appeared in Nature last December. “In an area of the world that people thought was in good shape, there are human impacts having a big effect.”

Haedrich and his team discovered the rapid decline of these fish by analyzing mountains of catch data from 17 years of deep-water fishing by Canadian researchers.

The authors of the study stressed that these fish populations were so low that they would be eligible for listing as “critically endangered species” under the guidelines of the International Union for the Conservation of Nature and Natural Resources, which maintains a “Red List” of hundreds of endangered plants and animals worldwide. The IUCN does not, however, formally evaluate deep-sea animals. “It’s a rat’s nest to get involved in,” Haedrich said, describing the massive and complicated international effort that would be required to convene an IUCN commission focused on deep-sea ecosystems.

Since the early 1970s, when deep-sea fish were heavily targeted by commercial fishing boats, population decline has outpaced scientific investigation. This leaves these poorly understood fish species at the mercy of unregulated fisheries. “We need a concrete effort to start having a look at these sensitive species,” said Denis Rivard, a senior policy advisor at Fisheries and Oceans Canada, echoing calls by many in the field.

The five species studied by Haedrich and his team are especially vulnerable to over-fishing because they can live as long as 60 years and don’t reach sexual maturity until well into their teens. Over-fishing can spell doom for such fish as it may take decades for remaining fish to replenish a population depleted by heavy harvesting.

Although there is not a North American commercial interest in any of the fish species that Haedrich and his team studied, accidental harvesting, or by-catch, is bringing about their demise. They frequent the same deep-sea habitats as heavily fished Atlantic species like Greenland halibut and redfish, and massive nets sent down to catch these species indiscriminately ensnare non-desirable fish as well.

Redfish in the northwest Atlantic are also facing severe population declines due to over-fishing, while Greenland halibut populations are remaining stable due to intensive regulations on the harvesting of this widespread species.

While none of the species Haedrich’s team studied is exactly fish stick material, two of them – the roundnose and onion-eyed grenadiers – are fished commercially in some parts of the world. A popular food fish in Russia and Spain, the roundnose grenadier, which can grow up to three feet long and looks “like a giant tadpole” according to Haedrich, is not fished commercially in Canada or the U.S.

While the exact ecological impact of drastic reductions in deep-sea fish populations is not yet known, the sheer magnitude of the losses rings alarm bells. “If you take 90 percent of a population out of communities of organisms, there are going to be consequences,” said Haedrich.

With poorly understood species declining so rapidly and uncertain ecological impacts looming, most scientists urge a cautious brand of conservation. Carl Safina, the renowned ecologist and co-founder of the Blue Ocean Institute, voiced a nuanced warning about human activity depleting such understudied species. He highlighted the need for conservation in the face of extinction by paraphrasing the father of modern ecology, Aldo Leopold. “The first rule of tinkering is saving all the parts,” he said.