Threatened species of Cetacea

Many of the world's whale populations have been over-exploited by the whaling industry to the point where it is believed that some of the remaining species are in danger of extinction. Eleven species of whale have been hunted, formerly for lamp oil and lubricants and presently as a source of oil for the manufacture of margarine, soap and glycerine, as meat for human and animal consumption, or for soups and flavourings. Sperm whale oil and spermaceti provide industrial scouring and hardening agents, lubricants and cosmetics. All of these products could be replaced by synthetic derivatives from vegetable and mineral sources, but it is still economically attractive to produce them from whales. Despite warnings that the catches were considerably larger than the stocks could withstand in the long term, whaling nations have allowed their industries to take almost as many whales as they could, arguing that they could not otherwise survive economically.

The whaling industry throughout the world is currently holding a three year moratorium on hunting ending in 1990. Japan and Iceland both kill whales for "scientific" purposes.

Large-scale industrialized whaling ended relatively recently. Today, although widespread hunting is no longer an issue, whales still face a litany of threats. Ship strikes cause terminal injuries, fishing gear strangles and entangles them, and ingested plastics block their guts, causing them to starve with full stomachs.  In 2018, thirteen sperm whales beached themselves in Germany, researchers found plastic garbage in the stomachs of four of the dead whales. Trash ingested by the dead sperm whales included a nearly 13-meter-long (43-foot-long) shrimp fishing net, a plastic engine cover, and the remains of a plastic bucket.

In the Antarctic the fin whale probably numbered 480,000 originally and in 1971; 77,000 (the maximum sustainable yield level is around 222,000 when they yield 10,000). The sei whales in the Antarctic have been fished intensively only since the early 1960s, when the fin whale declined most rapidly in numbers. In this time the sei whale stocks have been reduced from about 150,000 to 75,000-83,000 (this is above the maximum sustainable yield level of 52,000 which yields about 5,000). In the North Pacific the original stock of fin whales probably numbered about 43,500 and now stand at about 15,000 (the maximum sustainable yield level is 27,000 which yields 1,200). Sei whales have been reduced from about 70,000 to 46,000 (the maximum sustainable yield level is around 40,000 with a yield of about 3,000).

Because sperm whales reach sexual maturity at a late age—around 10 years for females and up to 20 years for males—and because they produce few young, their recovery has been slow. But perhaps given time and steadily increasing populations, large aggregations will occur and be documented more often. numbers are best considered for each sex separately, because of the difference in body size and behaviour in this polygynous species. In the North Pacific the initial population of males is estimated to have been 134,000 and there are now 64,000 remaining (with a sustainable yield of about 4,000 males). This stock is just above the population level required to maintain reproduction with the initial number of females, estimated to have been about 124,000 (the females are still well above the maximum sustainable yield level with a yield of about 5,000). In the Indian/Antarctic area, numbers are estimated at 20,000-49,000 (with sustainable yields of 1,000 of each sex).

A number of species which have been fished in the past are protected. Commercial hunting of right whales was banned in 1930, humpback whales in 1963, blue whales in 1965 and all great whales, including the grey whale, in 1967. Scientific whaling and hunting for the needs and lifestyles of indigenous peoples has been allowed since this time, and there is evidence of widespread abuse. The overall quota limiting the world catch set for the 1981 season was 13,900 whales, a sharp decline from the 46,600 killed per year a decade earlier. But even with protection, there is little sign that whale stocks, except for the California grey whale Eschrichtius robustus, are recovering. Some protected species have been deliberately caught in defiance of regulations or quotas which there are no means of enforcing. In 1993, the total world populations of the right whale, humpback whale and blue whale were 3,000 (formerly some 200,000 strong), 15,000 (Southern Hemisphere) and 700 (Southern Hemisphere), respectively.

Whales may be more threatened by human waste than weapons. One example is in the saltwater St Lawrence River estuary, home to about 400 beluga whales. During the 5 year period 1983-85 88 beluga carcasses laden with toxic chemicals have washed ashore. The whales were so polluted, said one biologist, that most were technically toxic waste.