THREATS TO WHALES
A century ago parts of the sea were teaming with whales. But human intervention changed this. The commercial whaling era killed millions of whales and made them into lamp oil, lubricants, cosmetics, and meal. Today, some whales are barely recovering from the whaling industry, while others have increasing numbers. But they face so many dangers other than whaling: pollution, loss of food sources, loss of habitat, climate change, toxic substances, being entangled in or ingesting plastic, sonar testing, net entanglement, trapped as incidental by-catch of the fishing industry, and ship strikes are some of the dangers maiming and killing whales.
No marine species remains unaffected by human activities. A viable population depends on the health of the ecosystem in which it exists, and the many forms of pollution extend to all the world's oceans threatening all species. Low-level contamination of the smaller prey species becomes concentrated in the tissue of larger marine predators and marine mammals.Planktonic organisms are carried great distances by winds and sea currents and larger nektonic creatures travel large expanses of oceans on their own accord. Both carry pesticides, heavy metals, and disease causing organisms to all sea areas. Contamination levels in toothed whales and dolphins are high. How this affects their individual fitness or their ability to reproduce is still largely unknown.
The beluga whale population of the St. Lawrence in Canada has been declining since protection in 1979. Through autopsies, researchers have discovered high concentrations of PCB and DDT, which are stored in the fatty tissues of mammals. Dead belugas have revealed bladder and liver cancer which has never been seen before in marine mammals. Other diseases found in belugas are hepatitis, splenic tumors, pneumonia, herpes, skin diseases, ulcers and blood poisoning, all of which suggest suppression of the immune system.
Toxicologists based in New York have completed research on elephant seals off Northern California coasts. They have found high levels of coplanar PCBs and skin diseases in this species. Along the west coast of the United States, autopsies of bottlenose dolphins show high PCB and DDT levels.
In addition to chemical pollution, oil slicks are commonplace in the oceans. Some whales and dolphins in the Western North Atlantic have been surfacing repeatedly through oil-slicked areas. In contrast, gray whales studies off of the Southern California coast changed their migratory path and their swimming and diving behavior when coming into contact with oil patches from seepage. Gill nets and fish traps kill thousands of marine mammals annually. Whaling hunting is practiced today by Norway, the Faroe Islands and Japan.
Noise pollution also threatens the existence of cetaceans. Large ships and boats make a tremendous amount of noise that falls into the same frequency range of many whales. This could be a contributing factor to the noticeable shift in the migration route of some California gray whales. Some are making a detour around the west side of the Channel Islands, possibly to avoid the noise pollution of Southern California sea traffic. Recent studies done in Newfoundland reveal that humpback whales entangled in gill nets have damaged ears. Since sound plays a vital role in the life of whales, dolphins and porpoises, noise pollution must be considered a significant cause of death as increasing numbers of whales are stranding where sonar testing is being conducted. This is one of the most prevalent dangers facing whales, large and small, today.