Featured Image Credit: www.nationalgeographic.com/magazine/
By: Eva Gruber
Entire mountains and mountain ranges lay submerged beneath the surface of our oceans. These underwater mountains, called seamounts rise thousands of feet from the sea floor, and stand waiting, as they have for millions of years, to be explored. Nobody paid much attention to these seamounts before the 1980’s until fishermen, forced by nearshore overfishing to venture out into deeper waters, began pulling up huge catches from them. Until then, seamounts were thought to be devoid of life and unremarkable scientifically. Boy, were we wrong.
Image source: National Geographic Mgazine and Waitt Institute
Seamounts are technically defined by oceanographers as conical in form and rising to at least 1,000 meters (3,281 ft) above the sea floor. Many of them are actually extinct volcanoes. If they broke the surface, they would be islands much like Hawaii or the Aleutian Islands.
In fact, the highest mountain on Earth, Mauna Kea, was a seamount that broke the surface and now makes up the Big Island of Hawaii. It rises 30,000 feet above the sea floor (so heavy that it presses down on the oceanic plate).
However, the majority of seamount peaks are many thousands of feet below the surface and take here place in the landscape within the deep sea.
Image source: www.oceanservice.noaa.gov
Types of Seamounts
Seamounts are as diverse in shape and size as they are numerous – each harboring its own story of formation. For example, a guyot is a seamount with a flat top. Over the course of its formation over millions of years, it breaches the surface. The peak then erodes and flattens over time due to weathering and wave action. As more time passes, the seamount slowly sinks below the surface again, becoming a “tablemount” or guyot.
Image source: www.scielo.cl
A total of around 9,950 seamounts have been mapped – this is only a fraction of those thought to exist. An even smaller percentage of these have actually been explored by scientists. So, there are still many seamounts to be discovered and mapped around the ocean basins – it is predicted that due to geological activity, a large amount of seamounts exist in the Pacific Ocean.
How to Discover a Seamount
Discovering a seamount requires a lot of modern technology, which is why so little is known about them. Only within the past few decades have we had the technology available to pierce the mysterious deep sea to be able to locate and chart seamounts.
Bathymetry is the study of the depth of the ocean floor and is measured in modern times through the use of ship-mounted sonar devices. The amount of time that it takes for a sonar ping to reflect back to the ship reveals the depth of the seafloor. Satellite altimetry is done, as the name suggests, from space. Orbiting satellites are used to send a microwave pulse of energy to the ocean surface, and then record the return time.
These incredibly sensitive and high-tech instruments have proven to be excellent tools for mapping our oceans, its currents, its features, and the amount and location of heat stored in the ocean which informs the study of climate change.
Image source: www.underseahunter.com
Submersibles (manned and unmanned) can also be used to explore seamounts, once they have been located. They can record observations, gather measurements and collect chemical/geological/biological samples, allowing us to put eyes and (robotic) hands at great depths – depths much greater than a human diver could go.
Life on a Seamount
Seamounts are one of the most common type of habitats in the world, due to their abundance and dominance of the ocean floor. New studies suggest that seamounts encompass about 28.8 million square kilometers of the earth’s surface – way larger than any single land-based habitat. And yet, due to the challenges and rigors of deep sea exploration, relatively little is known about the ecology of seamounts. Because of the way that seamounts influence currents, they often are areas of nutrient upwelling – supporting a productive and diverse ecosystem. This is why they are so often targeted by fishermen, as many of them support extensive fisheries. There is concern about this targeting, as most seamount fishing involves bottom trawling. Bottom trawling is one of the most destructive of fishing practices – where entire ecosystems are scraped (similar to clear-cutting a forest) off the seamount.
Image source: www.nationalgeographic.com/magazine
Because of the vast distances and depths between and among seamounts, no two seamounts may be alike, and some likely harbor life endemic to that one seamount, much like an island. Seamounts also can be hotspots of biodiversity rising up from what is often compared to as the barren desert that is the seafloor. Marine biologists still have a lot of exploration, sampling, collecting, and classifying to do so that we can fully understand the ecology of seamounts and their influence on the diversity and health of the oceans.
Look at this stunning National Geographic gallery of lifeforms from seamounts around the world.
Orange Roughy
One of the most well-known case studies of overfishing on seamounts is of the slimehead (Hoplostethus atlanticus), or orange roughy as it was re-branded to increase its appeal in the seafood market. This fish occupies many seamounts across the western Pacific and eastern Atlantic, and is notable for its lifespan of at least 149 years. However, due to its flesh being considered a delicacy, it is targeted by commercial fishers and has since been classified by the Marine Conservation Society as “vulnerable to exploitation”. This is due to its natural history as a slow-growing, long-lived fish with relatively low reproductive rate. Many stocks have already crashed beyond recovery, and the remaining ones are in no way sustainable at current fishing rates.
In fact, a joint report by TRAFFIC Oceania and the World Wildlife Foundation’s Endangered Seas Program argues that, “probably no such thing [exists] as an economically viable deep-water fishery that is also sustainable. Similarly, international agreements to reduce fishing capacity, to remove subsidies which encourage overfishing, to encourage co-operation in management of fish stocks and flag States to take responsibility for their vessels fishing on the high seas, appear to have gone largely unheeded, to the detriment of deep-sea species and their associated ecosystems.” For more information, look here.
Image source: fiesta.bren.ucsb.edu
Seamount Threats
Some of the higher seamounts pose a hazard to seagoing vessels. Muirsfield Seamount is named after the ship that struck it, sustaining heavy damage to the keel. However, the most likely threat that seamounts pose is when, due to instability from old age, their sides and flanks slough off causing an undersea landslide which has the potential to trigger a massive tsunami.
But really, we humans pose more of a threat to seamounts that seamounts do to us – through overfishing and bottom trawling. Nearly 80 species of fish are targeted on seamounts, but when the bottom is trawled, the whole ecosystem is destroyed. When we demand unsustainable seafood, commercial fisheries are inclined to fish wherever and however they can with no regard to long-term fisheries stocks. The best choices we can make are informed by scientists. If you eat seafood, the best thing to do is consult Monterey Bay’s Seafood Watch Program to check if what you are eating is not in danger of becoming threatened or extinct.
For more information, read more from our sources: Woods Hole Oceanographic Institute and Seamount Catalog