marine science oceanography facebook marine conservation society website home news london meetings courses contacts seasearch calendar marine based activities newsletter marine science education sitemap marine life world news

The Orange Roughy

Orange roughy are one of the stocks that are frequently overfished at seamounts.

Scientists estimate that it could take decades before these local stocks are able to recover.

Orange roughy


A deep-sea fish also known as the “slimehead,” orange roughy grows slowly and reproduces late in life. These traits make it especially vulnerable to overfishing.

Consumer Note

Orange roughy lives 100 years or more—so the fillet in your freezer might be from a fish older than your grandmother! 

Health Alert

Environmental Defense Fund has issued a health advisory for orange roughy due to high levels of mercury. 


Years of heavy fishing have decimated orange roughy populations. Although there are fishery management plans in place, scientists predict it could take decades for populations to recover.

Another concern with orange roughy is the way it’s caught. Bottom trawls are problematic, causing damage to seafloor habitat, especially in the fragile, deep-sea ecosystems where orange roughy live. For these reasons, orange roughy are ranked as a species to “Avoid.” 

Deep Sea Corals

In recent years scientists have discovered deep-sea corals and/or coral reefs in Japan, Tasmania, New Zealand, Alaska, California, Nova Scotia, Maine, North Carolina, Florida, Colombia, Brazil, Norway, Sweden, UK, Ireland and Mauritania. Because research submarines and remotely operated vehicles suitable for studying the deep sea are few and expensive to operate, scientific investigation of these remarkable communities is in its very early stages. But it is increasingly clear that deep-sea corals usually inhabit places where natural disturbance is rare, and where growth and reproduction appear to be exceedingly slow. Deep-sea corals and sponges may live for centuries, making them and the myriad species that depend on them extremely slow to recover from disturbance.

Unfortunately, just as scientists have begun to understand the diversity, importance and vulnerability of deep-sea coral forests and reefs, humans have developed technologies that profoundly disturb them. There is reason for concern about deep-sea oil and gas development, deep-sea mining and global warming, but, at present, the greatest human threat to coral and sponge communities is commercial fishing, especially bottom trawling. Trawlers are vessels that drag large, heavily weighted nets across the seafloor to catch fishes and shrimps. Scientific studies around the world have shown that trawling is devastating to corals and sponges. As trawlers become more technologically sophisticated, and as fishes disappear from shallower areas, trawling is increasingly occurring at depths exceeding 1,000 meters.



You are here: Home > Marine Science > Marine Ecology > Marine Habitats > Seamounts

What are seamounts?
Seamounts are undersea mountains (usually of volcanic origin) rising from the seafloor and peaking below sea level. Underwater mountains of heights above 1000 m are considered to be seamounts, those between 500-1000 m as knolls, and those below 500 m as hills. A seamount tall enough to break the sea surface is called an oceanic island, e.g., the islands of Hawaii, the Azores and Bermuda were all underwater seamounts at some point in the past.

Map of underwater seamounts
Click on image to inlarge

Though most people may be unaware of it, underwater seamounts are fairly common. Estimates vary, but recent studies suggest that there may be about 30,000 seamounts of heights over 1000 m in the Pacific Ocean, about 1,000 in the Atlantic Ocean and an indeterminate number in the Indian Ocean.

Why are seamounts so important?
Seamounts are hotspots of marine life in the vast realms of the open ocean. As they stand proud of the surrounding seabed they tend to concentrate water currents and they can have their own localised tides, eddies and upwellings (where cold, nutrient-rich, deepwater moves up along the steep sides of the seamount).

Due to the strong localised currents and upwellings, the plankton biomass is often high over seamounts and this combined with the constant influx of prey organisms, means that they can attract large numbers of fish.

Marine mammals, sharks, tuna, and cephalopods all congregate over seamounts to feed on the rich booty and even seabirds have been shown to be more abundant in the vicinity of shallow seamounts.

Down on the seabed, volcanic rocks provide lots of space for suspension feeders such as corals that capitalise on all the food that is swept around them in the strong currents. This is in sharp contrast to the typical deep-sea habitat where deposit-feeding animals rely on food that they eat on or in the sediment.

Though the diversity and exceptionally localized distribution of species living in these unique communities are acknowledged, their biology and life history remain poorly studied, except for indications that some of these species may be extremely long-lived; some are thought to live for more than 100 years.

Due to the large stocks of top predators, species diversity and uniqueness compared to the surrounding ocean, seamounts are often called "oceanic oases".

Threats they face – overfishing and why are seamounts so vulnerable?
Global fish catches have declined steadily since the 1980s, and it is now widely acknowledged that the world’s fisheries resources are in serious danger of depletion, undoubtedly due to poor management practices and increased fishing pressure. Unsustainable fishing practices along with an excessive level of investment in fishing capacity have resulted in serious stock depletion on most continental shelves, thus creating new pressures on alternative fishing grounds. In particular, seamounts are among those "newly" targeted ecosystems that, since the second half of the 20th century, have been intensively fished.

Deepwater fisheries in general and seamounts fisheries in particular, exhibit a boom and bust sequence, crashing within about ten years of their initial development. This was the case with the orange roughy (Hoplostethus atlanticus) fisheries off New Zealand, Australia, and even in the North Atlantic, the pelagic armourhead (Pseudopentaceros wheeleri) fisheries over seamounts in international waters off Hawaii, and the blue ling (Molva dipterygia) fisheries in the North Atlantic. As seamounts are rapidly depleted, the continued existence of the fisheries on them depends upon the discovery of unexploited seamounts with large fish aggregations.

The species targeted by fisheries at seamounts have a very low overall abundance, but they aggregate at seamounts as part of their life cycle strategy, e.g. for spawning. They are often long-lived, slow growing, late maturing (at about 30 years), and have low reproductive potential.

Therefore if they are fished out, it is thought that it could be decades before these localised stocks recover; particularly as they are thought to have limited exchange with other seamounts. This makes these fish communities very vulnerable to overfishing and the problem is even more pronounced in seamounts located in international waters where effective management strategies and agreements are frequently absent.

Depletion of fish stocks is not the only concern. Extensive trawling activities on seamounts are damaging benthic (bottom living) communities, particularly dominant communities of corals and other suspension feeders. The impact of trawling on complex seamount reefs appears to be dramatic, with the result of the complete removal of coral substrate and associated community from the most heavily fished seamounts. Such massive removal of natural and structural components of the ecosystem has negative consequences on seamount biodiversity.

Evidence of such negative impacts has been recorded by declining fish stocks associated with seamount fishing in Australia. There are also concerns that damage by deepwater trawling to coldwater coral reefs in the NE Atlantic, could extend to seamount areas. Unregulated small-scale fishing can also disturb these sensitive environments, e.g., the decline in important fish stocks exploited by small-scale fisheries in the Azores.

Outlook for the future 
There is a rising concern about the threats to seamount ecosystems in the Exclusive Economic Zones of coastal states and in the high seas and consequently, Canada, Australia and New Zealand have begun to take the first steps towards protecting seamounts. In the Atlantic, no such protective measures have been established but the OSPAR Commission has placed seamounts on their initial list of threatened and declining species and habitats that require conservation action. Mechanisms to provide this protection will now be considered. The developing OSPAR Marine Protected Areas programme should provide one possible mechanism.

In addition, seamounts dominated by hard substrata in the waters of the European Community may qualify for site protection under the European Habitats Directive (1992, Natura 2000 code 1170 "reefs" in the Interpretation Manual of European Union Habitats EUR 15/2). Portugal (Azores Region) may nominate one of the seamounts in their EEZ as a candidate for a Marine Protected Area (MPA) under the OSPAR convention.

From deep on the ocean floor at the mid-Atlantic ridge, huge undersea volcanoes rise up from the deep, with their own unique eco-systems and communities of undersea life on each of them, feeding on the marine snow. Video clip from the BBC Planet Earth series.

Home  |   News  |   Meetings  | Courses  |  ContactsMarine Sciences  |  Things to do | Marine World News | Sitemap |