Sound travels four times faster in water (1,230 meters/sec.) than in air (340 meters/sec.) because water molecules are packed tighter
together. This results in sound that will also travel farther under water. High intensity sound in the oceans can travel for thousands
of miles. In this regard it is important to remember that since water has a much greater density than does air that sound waves
travel though water at much higher energy levels and are hence louder.
We know that whales and dolphins use sound to communicate with each other over vast distances. Other marine species use sound to find food and choose mates as well as warn others of potential dangers. Whales communicate at very low frequencies, below 1000 Hertz. This is the same frequency that resonates from many human-caused activities. Man-made sounds are drowning out the calls of mates, calves and other pods that these mammals depend on. High sound levels cause grey whales to deviate from their migration paths, the deviation being greater as sound intensity increases. Full text at: SEE-THE-SEA.org
1. Ships create noise from their propellers, motors and gears. The amount of noise produced depends on their hull shapes and propulsion systems. Most of the noise ships produce is at low frequencies (roughly 20–500 Hz). In the frequency range of roughly 500–100,000 Hz, however, ambient noise is mostly due to breaking waves, rather than shipping. At low frequencies the background sound level in many places in the ocean is dominated by noise from distant ships, even when there is no nearby ship. When a large ship passes close to a receiver, the noise that is generated will temporarily increase the sound levels at that location substantially. Details.....
2. Military strong naval sonar through the deployment of Low Frequency Active Sonar Some systems operate at more than 235 decibels, producing sound waves that can travel across tens or even hundreds of miles of ocean. During testing off the California coast, noise from the Navy's main low-frequency sonar system was detected across the breadth of the northern Pacific Ocean. By the Navy's own estimates, even 300 miles from the source, these sonic waves can retain an intensity of 140 decibels -- a hundred times more intense than the level known to alter the behavior of large whales.
3. And, through oil and gas exploration and associated drilling.
From the extreme noise generated during exploration for oil or gas to the threat of oil spills, all aspects of oil and gas exploration and production are a potential threat to whales and dolphins and need careful management to avoid excluding whales and dolphins from their homes and causing them harm. High levels of underwater noise is generated during all stages of oil and gas production, though the exploration, installation and decommissioning stages are likely to produce the greatest amounts of noise. Details.....
4. Then there are other types of pollution, i.e. DUMPING - chemicals, illegal radioactive waste, oil spills, plastic ....the list
To some, the deep-sea floor may seem safe from the human disturbances that threaten terrestrial and coastal ocean environments.
Yet, most natural and artificial wastes -- such as sewage sludge, mining tailings, fly ash from power stations, dredged spoils from
harbors and estuaries, dangerous synthetic organic compounds and packaged goods make their way to the sea floor over time. On the left is a
picture of a dead seal with a circular plastic around its mouth.... Full text at:
Most reports of collisions between whales and vessels involve large whales, but all species can be affected. Collisions with large vessels often go unnoticed (or unreported if noticed). Animals are injured or killed and vessels can sustain damage. It is thought that the proximity of ships' propellers noise affects whales orientation's ability. Serious and even fatal injuries to passengers have occurred involving hydrofoil ferries, whale watching vessels and recreational craft. Ship strikes are an international problem. Accounting for and reducing the impact of commercial shipping on the oceans' environment, while achieving commercial sustainability, is of increasing importance, especially as it relates to the influence of cumulative noise "footprints" on the great whales.
Above: June 2012, The Mont Ventoux, a cargo ship of the CMA-CGM shipping company, brought back on its bulbous bow a 19-meter fin whale in the Port of Marseille. The necropsy carried out by the members of the National Stranding Network (Réseau National d’Echouage) revealed that the whale was a lactating female; very probably an unweaned calf has almost no chance of surviving in the wild without its mother.
Above _ Multi-species stranding involved 189 pilot whales and 10 dolphins in Naracoopa, Tasmania. This occurred in 2009 and has been linked to seismic surveying operations occurring in the area.