On average, around 2,000 cetaceans (marine mammals such as whales and dolphins) are washed onto shores, called stranding, every year. Strandings typically include an individual animal, however mass strandings do happen and can involve several animals at the same time. Strandings are unpredictable events and there are numerous reasons that help explain this anomaly. Once a whale or dolphin is beached, it dies from dehydration, being crushed under its own weight, or when their blowhole is covered by the rising tide. In most cases, the definitive reason is still unknown as to why they beach in the first place but the following explanations hold some insight into the possibilities for why it occurs.
Natural Causes
Throughout history, whales that have been found beached, have been attributed to environmental or natural factors such as,
- Whales can become infected with a number of various diseases. It might be a temporary affliction or something more extreme. The impacts of such disease leave them weak and disorientated, or with impaired echolocation and they strand. There has been a high incidence of pneumonia seen in stranded whales.
- Old whales might find it hard to keep up with their pod or resist heavy swells or inshore currents. Because of failing strength these animals might strand. For the most part they are observed to be in weak health.
- While chasing prey, whales might accidentally beach themselves by chasing potential food sources into shallow waters.
- Some dolphins may also come too close to shore to avoid predators like the orca.
- Gentle graded, sandy shorelines may not reflect echolocation signals back to the whale, leading them to believe they are in deeper water. Combined with a fast dropping tide, whales can quickly become trapped.
- Calving whales will often seek out sheltered coves to give birth to their young. If they come too close to the shore, they might strand. Whales that are experiencing birthing issues are more likely to strand.
- Unfamiliar coastal configuration or uncommon weather patterns, especially electrical storms, may also make whales strand through navigational errors.
Man-Made Causes
- Underwater explosions, artificial sounds caused by vessels, and seismic testing can devastatingly affect whales. These noises disrupt their listening ability and influence their capacity to communicate, hunt and navigate.
- There have been strandings strongly associated with use of active sonar called low frequency active sonar (LFA Sonar) used by military groups to locate submarines. A report emerged from the National Marines Fisheries Service stating that the U.S Navy sonar exercise implemented near the Bahamas in 2000 led to a mass stranding of 17 cetaceans. Of the seven that were killed, the necropsies revealed that their cause of death was linked to acoustic hemorrhaging. The LFA Sonar sound is the loudest sound to have ever been put in the ocean.
- Whales also can become debilitated by strong net entanglements left in the water or can sustain serious wounds and injuries by collisions with vessels. They can sustain, for example, broken teeth and jaws, deep cuts, flipper dislocations or fractures, spinal or muscle harm or severed fins or flukes. Any injury like this can lead them to strand.
- Toxins can also harm whales. Since they are at the top of their respective food chains, pollutants eaten by whale’s preferred food sources tend to bio-accumulate in their fat.
- Mass strandings can also occur when one animal has found himself in a predicament and he sends out a stress call, to which the rest of his pod will respond and become in a similarly helpless situation and eventually strand.
- A deficiency of food caused by the overfishing can also bring about malnourished whales. Separated dependent calves and old adults might also be malnourished. Tragically numerous stranded whales have been found with substantial volumes of litter or plastic in their gut. Ingestion of these materials can lead to disease and malnutrition.
Although conclusive reasons for why whales beach has not been uncovered, there are several viable factors and combinations of factors that are contributing to the many strandings we see every year.