for National Geographic News
Rising from the depths of the North Atlantic, seamounts are described by conservationists as oases of life. The underwater volcanoes harbor a vast array of deep sea creatures, many of them still unknown to science. They also attract large numbers of fish, which in turn have attracted the attention of commercial fishing fleets. Environmentalists now say such attention could destroy these precious ecosystems.
A report published last month identifies commercial fishing as the major threat to the biodiversity of seamounts in the North Atlantic, while marine scientists are calling for urgent conservation action to protect seamounts worldwide.
The report was published jointly by World Wildlife Fund (WWF) Germany and the Oceanic Seamounts: An Integrated Study (OASIS) project. The latter involves marine scientists throughout Europe and is funded by the European Union. The study aims to shed light on the natural history of seamounts in the northeast Atlantic Ocean and their contribution to the ecology of the surrounding ocean.
Many important commercial marine species congregate on seamounts, according to the report's author, Susan Gubbay, an independent marine ecologist based in the U.K. They include the black scabbard fish (Aphanopus carbo), blue ling (Molva dipterygia), morid cod (Mora mora), orange roughy (Hoplostethus atlanticus), shovel nosed shark (Deania calceus), and tusk (Brosme brosme).
Gubbay writes that the fish species "have been the targets of intensive exploitation" through a variety of commercial fishing methods, including longline fishing, mid-water trawling, and bottom trawling that can operate at depths of more than 1,500 meters (4,900 feet).
Scientists say such exploitation has been fueled by the collapse of shallow-water stocks due to overfishing. This switch of focus to offshore waters is blamed for population crashes in fish like the orange roughy and blue ling, which gather in dense shoals around seamounts and are easily targeted by trawlers. In the northeast Atlantic these trawlers come mainly from France, Ireland, the Faroe Islands, Greenland, and Norway.
The report also highlights concerns over other vulnerable deep sea fish inadvertently taken as by-catch. "One ton of fish is discarded for every ton of fish landed," Gubbay wrote.
While baited longlines can stretch 50 kilometers (31 miles) and carry over a thousand hooks, scientists consider bottom trawling, in which large, weighted nets are dragged along the seafloor, to be most damaging to seamounts. The method destroys or disturbs delicate, slow-growing seabed communities. For instance, some cold water coral reefs discovered on seamounts are believed to be more than a thousand years old.
Seamounts are cone-shaped, volcanic mountains that rise as much as five kilometers (three miles) from the seabed and can measure 100 kilometers (62 miles) across. There are over 800 of them in the North Atlantic alone. Often they are isolated, and, like some of their counterparts on land, scientists suspect they support large numbers of endemic species. Up to 50 percent of species observed during recent explorations to seamounts have been new to science.
The steep slopes of the deep sea mountains amplify ocean currents, providing ideal conditions for corals, sea-anemones, and other suspension feeders that attach themselves to rock faces. Plankton concentrations are higher than elsewhere, laying the foundation for a food chain that builds to big fish predators such as swordfish (Xiphias gladius) and shark species. Seamounts are also considered important nursery areas for deep sea fish.
Like the corals and sponges, many of these fish are long-lived and slow to mature. For instance, the orange roughy can live 150 years, and takes 25 to 30 years to reach sexual maturity. Conservationists say this makes the fish particularly vulnerable to overfishing.
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