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The launch at the dawn
of the day at Cashes Ledge
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Surrounded by a lacy net of bubbles, scientists descend through the Gulf of Maine to an undersea area known as Cashes Ledge. A submerged mountain range, Cashes Ledge is a hidden place, full of life and color and drama, lying a short distance beneath the waves.
Johnson Sea-Link, a manned submersible from the Harbor Branch Oceanographic Institution, dives over Cashes Ledge.
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Cashes Ledge is located about 80 miles (129 kms) east of Gloucester, Massachusetts. Formation of the range took place soon after the last glacial age. Approximately 13,000 years ago, melting glaciers sent rivers and streams coursing across the Gulf's then-dry landscape, cutting channels in the land and eroding stream valleys. Erosion-resistant rocks, such as those that make up Cashes Ledge, slowly became mountains while the surrounding softer rocks eroded into deep basins. As the glaciers continued to melt over time, the dry land receded beneath the ever-rising sea, submerging the now-variegated landscape beneath the waves.
The peaks of these mountains rise within 40 to 100 feet (12 to 30 m) below the sea surface. Long known to fishermen as a rich fishing area, the ragged mountain tops presented a threat to their bottom-hugging nets. It was all too easy to snag a valuable otter trawl on the upthrust rocks, losing both the catch and the net. With a wealth of fish to catch in other parts of the Gulf, the Cashes Ledge area was left relatively untouched by commercial fishermen well into the 1980s.
Johnson Sea-Link exploring the side-wall of Cashes Ledge
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During the 1980s, scientists began to be interested in the Cashes Ledge area simply because it had not been repeatedly fished during past decades. They hypothesized that the area might provide insights into what the larger Gulf of Maine had been like before the onset of modern commercial fishing.
The highest peak of Cashes Ledge, Ammen Rock, lies just beneath the water's surface. Dr. Robert Steneck of the University of Maine Darling Marine Center spent several years studying the Cashes Ledge area in the late 1980s. He found that, unlike most other sections of the Gulf of Maine, Ammen Rock and its environs still retained big predatory finfish, such as cod, pollack, wolf fish and sharks, most of whom had been fished out in other areas.
Sea Raven, also known as the Red Sculpin
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Steneck noted that in his study area, Ammen Rock held almost no mobile benthic invertebrates, such as lobsters or crabs. Larger predatory fish are known to eat the juveniles of both species. Perhaps before the over-harvesting of groundfish throughout the Gulf of Maine, groundfish were the Gulf's dominant species, keeping animals such as lobsters, today extremely abundant, in check.
Johnson Sea-Link's pilot maneuvers around Cashes Ledge.
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Part of the lure of Cashes Ledge to divers and recreational fishermen is the rich trove of life to be found there. Whales, sponges, and fish depend on the nutrients and plankton spilling over the mountains with the Gulf of Maine current. In the spring and early summer months, humpback whales visit the area, gathering great mouthfuls of plankton- rich seawater in their accordian-like gullets.
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Diving on Ammen Rock is to be enveloped in biology. Because it sticks up into the water column, Ammen Rock creates an obstacle to the dominant Gulf of Maine current. Like a rock in the midst of a river, its position causes smaller currents to swirl and stream about it. These smaller streams of water send volumes of nutrient-rich water past its many surfaces, providing a rich larder to the many organisms found there. The peak of Ammen Rock lies well within the photic (or light filled) zone and is covered with bottom-dwelling algae. Horse mussels hide away among lush forests of kelp. Ammen Rock is noteworthy for having one of the deepest seaweed communities in the world.
Shrimp perching on red sponge
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Passing over the edge to the vertical wall of Ammen Rock, one sees wall-to-wall multicolored anemones and sponges. Deeper along the wall, brachiopods, sponges, and low, bumpy algae are nestled together. Cod, pollack, and an occasional wolf fish swim around the rock, seeking food or a protected nook in which to hide.
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Images and Video ©Bill Curtsinger,
All Rights Reserved
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