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Threats to Whales and Dolphins |
Entanglement & Bycatch
Injury or death of cetaceans in fishing gear (or occasionally cables) is a worldwide problem. This usually occurs accidentally in fishing nets and is then called ‘bycatch’. The usual cause of death is from drowning, as animals are held away from the surface for extended periods. Non-fatal injuries also occur. Driftnets and gillnets are a particular cause for concern (the former are being phased out by the EU). The extent of bycatch worldwide is hard to measure. In the EU, where bycatch has been estimated in some fisheries using observers on fishing vessels, the estimates of numbers caught have raised serious concerns.
Bycatch - JNCC
Pollution
Man-made chemical pollutants include factory effluents, plastic waste, sewage and agricultural run-off. Many such chemicals are toxic to cetaceans and can result in immunological or reproductive disorders. Ingestion of plastic waste in the sea can also cause internal injury. Cetaceans may also be affected indirectly, because as top predators they can accumulate toxins from their prey. Coastal areas and rivers are particularly prone to pollution events.
Another pollutant is man-made noise. Since the advent of motorised ships and the increase in shipping traffic the level of background noise in the ocean has increased significantly. Other major noise sources are oil prospecting or drilling, and military sonar. To communicate and forage in their dark or murky habitat, cetaceans have evolved an acute sense of hearing. Noise may interfere with communication or induce discomfort. In more extreme cases, sudden loud noises can cause serious, even fatal, physical damage (including permanent hearing loss and internal lesions) or displacement from habitats.
Hunting
Many whale populations have been reduced to remnants of their former numbers by commercial whaling. For example, from an initial population of 250,000 blue whales in the Southern Ocean only around 1000 now remain. Even though blue whales have been protected since 1967, it is only now that the first tentative signs of recovery are emerging. Northern right whales, protected since 1935, are still hovering on the verge of extinction. In contrast, southern right whales (also protected since 1935) are exhibiting a dramatic recovery. However, for most populations of whale, the levels of uncertainty are so great that we have no indications of any trends in numbers, either up or down.
| Some significant events in modern whaling |
|---|
| 1865 |
Invention of explosive harpoon |
| Early 1900s |
Establishment of Antarctic whaling |
| 1935 |
Right whales are protected |
| 1946 |
IWC Convention set up by a number of whaling countries |
| 1963 |
Britain sells last whaling ship to Japan |
| 1967 |
Complete protection for the blue whale |
| 1982 |
IWC adopts a ‘moratorium’ on commercial whaling |
| 1986 |
IWC moratorium comes into effect |
| 1994 |
IWC declares the Southern Ocean a Sanctuary for whales |
| 2003 |
IWC establishes a Conservation Committee
to address all conservation threats to whales and dolphins |
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| Figure 1. Reported catches of baleen whales in the southern hemisphere over the 20th century. Whalers targeted a succession of species, moving from one to the next as each became depleted. These figures do not include illegal Soviet catches.© IFAW. |
Despite the International Whaling Commission (IWC) ‘moratorium’ (i.e. suspension), whaling by Japan, Norway, and Iceland continues. Minke whales, which were at one time considered too small to be worth hunting, are the most recent species to be exploited. Around 1,300 whales are killed each year.
Subsistence hunting by aboriginal peoples is not prohibited by the IWC moratorium on commercial whaling. For example, grey whales are hunted by Russian Inuit and occasionally taken by the Makah tribe in the western US. A strict interpretation of the IWC aboriginal whaling provision is that a continuing nutritional subsistence need for whale meat to be demonstrated. Requiring that whale products are consumed by those that catch them means that aboriginal whaling is therefore small-scale.
Collisions
Records of collisions between whales and ships begin in the late 1800s and increased thereafter, coinciding with increases in the speed and number of motorised vessels. Collisions have been recorded involving all types of vessels, but fatalities are more likely with fast and/or large boats. High-speed vessels such as hydrofoils may pose a particular threat. Injuries (fatal and non-fatal) include cuts, haematomas, fractures/breakages and severances. It is difficult to gauge the full extent of the problem because often the cause or extent of injuries (which may be internal) cannot be determined, and in any case many dead animals may not be found. Pilots of larger boats may often be unaware that a collision has taken place.
Geo Files - National Geographic
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