As early as 1490, Leonardo da Vinci found that by stopping a boat and placing a long tube in the water, he could detect the sounds of a far-off boat along with other unidentified sounds. He had discovered that sound waves were transmitted through water. Then, in 1826 on Lake Geneva, Switzerland, three scholarly individuals used the simultaneous flash of gunpower and ringing of a submerged bell to measure how fast sound traveled underwater. It was ultimately determined that the speed of sound underwater is 4.3 times faster than in air; its underwater speed is 3,300 mph, while in air is 767 mph.
During WW1, detection of enemy submarines relied either on spotting them on or near the surface or using rudimentary sound detection systems. During that war, about 200 U.S. merchant vessels were torpedoed by U-boats. Unfortunately, after declaring war on Germany on December 11, 1941 (Pearl Harbor December 7, 1941), our Navy was still ill-prepared for the onslaught of U-boat attacks. In the first three months of 1942, an estimated 100 American merchantmen and oil tankers were sunk by enemy submarines off our East Coast, Gulf of Mexico and the Caribbean Sea.
In 1940, while testing underwater listening devices (hydrophones) in Chesapeake Bay waters, researchers recorded strange noises They were eventually identified as spawning Atlantic croaker fish. During the early development of the Navy’s acoustic technology, SONAR operators had difficulty differentiating bizarre marine life sounds from those produced by various ships. In December 1941, while on patrol off the Philippine Islands, the USS Salmon (SS-182) detected what was assumed to be propeller sounds. But after surfacing, they only found an “empty exposed of moonlit ocean.” The same was experienced by other Nary ships. However, over the next few years of the war, the advancement in hydrophones allowed detection of enemy vessels without revealing their own ship’s location. Advancements in aircraft radar systems also greatly assisted in spotting enemy submarines.
Following the war, the Navy called on marine biologist Marie Fish to investigate the mysterious underwater sounds frequently encountered by SONAR operators. She was quick to state that the source was created by marine animals. Supported by the Office of Naval Research, Marie worked out of the University of Rhode Island for nearly two decades, investigating more than 180 marine species for sound production.
It was ultimately determined that the ocean’s loudest creatures were sperm whales. Their clicking sounds reach a level of 230 to 236 decibels. A 1-ton conventional TNT bomb produces a blast reaching 200 decibels. Snapping shrimps inhabit tropical waters along with certain shallow sites in Long Island Sound. As they quickly snap their oversized claw, they create an explosive cavitation bubble that produces a sound that can reach 200 decibels. Other residents of the Sound, such as striped sea robins, also produce sounds. They generate barks, growls and clucks. During spawning season, they create staccato clicks. Weakfish create a drumming or thumping sound while northern seahorses produce clicks during courtship and while feeding. In the world’s oceans, an estimated 1,000 species of fish contribute to underwater sounds. Even blue mussels create sound when changing their position for protection or capturing food. From late November to mid-March and early May, harbor seals inhabit Long Island Sound. During their mating season, the Sound’s harbor seals create soft, low noises. However, when annoyed or threatened, they produce a snort or hisses.
When Scuba diving the Sound, the most likely encountered sound producers are oyster toadfishes. Also known as the oyster toad and ugly toad, they produce two distinct sounds, a grunt or a boat whistle call at 100 to 110 decibels. After establishing a nest under a boulder or other submerged object, the male begins trying to entice a mate with its call. When a receptive female enters his nest, she turns herself upside down and lays her adhesive eggs on its upper surfaces. After she leaves, the male releases his milt to fertilize the eggs. He then guards the brood through hatching and until they can swim away. Though anything but beautiful creatures, it is rewarding to hear their sounds and view a male protecting his developing youngsters.