|Home > Reports Stories & Views > Dwindling Fish Stocks|
Whales are Not the Major Causes of Dwindling Fish Stocks
National Oceanic & Atmospheric Administration
US Department of Commerce
Do whales and other marine mammals compete with humans for fisheries resources? Should whales be hunted to save fish stocks? Today's marine science community has enough expertise and experience with the complex ocean ecosystem to recognise that the "competition" claim is oversimplified and the hunting proposal is biologically unsound.
As a whole, whales do not eat "large quantities of fish as food," nor do they threaten the health of the world's limited marine fish resources. Some whale Species do prey on fish, but often on fish that humans do not consume. In truth, humans are primarily responsible for fisheries declines. It is humans who continue to threaten the world's stocks through overfishing and reluctance to allow stocks to naturally replenish.
To date, fish consumption by whales being characterised as competition with humans for fish has been based on misleading data that ignore the dynamics of extremely complex marine ecosystems throughout the world. Let us share the known facts.
Fish Resources Known to be Declining/Overfishing Blamed
The United Nation's Food and Agricultural Organisation's recent "State of the World's Fishery Resources" report concluded that approximately 60 percent of the world's major fish resources are showing declining yields. The FAO concluded that the desired annual increase in world fish stocks of at least 10 million tonnes could be achieved by reducing fishing effort and increasing yield-per-recruit (in other words, increasing age at first capture, prohibiting exploitation of young fish, increasing net mesh sizes, and closing areas utilised by young fish). However, the FAO did not make the suggestion that the lethal removal of whales will help the recovery of over-exploited fish populations.
Numerous scientists around the world have reported on the depleted or declining status of various fish populations. Some examples of fish population collapse caused, at least in part, by overfishing include the sardine stocks off California and Japan in the 1940's, herring in the North Sea in the 1970's, anchovies Peru in 1972, and capelin in the Barents Sea in the 1980's. Other recent examples include the cod populations off Canada and the groundfish populations off New England.
What Do Whales Eat? Species Benthic
Fin Whale 0 0.8 0.05 0 0.05 0.05 0.05 Blue Whale 0 1 0 0 0 0 0 Minke Whale 0 0.65 0 0 0.3 0 0.05 Sei Whale 0 0.8 0.05 0 0.05 0.05 0.05 Bryde's Whale 0 0.4 0 0 0.2 0.2 0.2 Humpback Whale 0 0.55 0 0 0.15 0 0.3 Gray Whale 0.9 0.05 0 0 0 0.05 0 Sperm Whale 0.05 0 0.1 0.6 0.05 0.05 0.15 Relative proportions of eight prey categories in the diet of selected large whales (from Panley et al., 1998) Data for Northern and Southern Hemispheres are combined.
Fish, Not Whales, Eat Most of the World's Fish.
Piscivorous fish, or fish that feed on other fish, are major consumers of fish eggs and larvae, which is a problem in many fisheries. For example, predation of herring eggs by cod in Norway has been reported to cause a major loss of herring eggs. Cod predation has been reported as a significant source of fish loss for fisheries in the Baltic Sea.
Overall, predatory and cannibalistic fishes consume vastly greater amounts of commercially valuable fish than do marine mammals. In the Bering Sea, marine mammals have been reported to feed on 1.1 million tons of pollock annually. Predation by other fish was estimated to be 2.7 million tons, and cannibalism accounted for 7.4 million tons annually.
One study compared fish loss to predators (including fisheries) among six marine ecosystems. The analysis showed that in all six ecosystems, loss from predatory fish accounted for more than 50 per cent of total fish loss.
Whales Usually Do Not Prey on the Same Fish Species as Fishermen
Many of the fish species consumed by whales are not of commercial interest or suitable for human consumption. In most instances whales are not in direct competition with fisheries.
In the Pacific Ocean direct competition between marine mammals and fisheries is limited because more than 65% of the food consumed by whales and other marine mammals consists of deep sea squids and deepwater fishes not harvested by humans.
Many important fisheries, such as those for tropical tunas, occur where whales are not feeding. In addition, many important whale feeding grounds, such as those in the Antarctic, are in regions that are insignificant to the harvest of fish for human consumption. Moreover, Southern Hemisphere baleen whales predominantly eat krill, not fish. In many cases whales feed on fish that are inaccessible to fishermen or unsuitable for human consumption, such as watery deep sea squids consumed by sperm whales and the very small deep sea fishes consumed by small whales and dolphins.
Ecosystem Complexities Must Be Considered
Ecosystem management is difficult because marine scientists do not yet understand ecosystem dynamics well enough to be able to accurately predict the outcome of any particular manipulation. However, scientists do know that hunting whales to save fish is unlikely to increase the number of fish in the sea. In actuality, other ocean predators might increase their levels of predation if fish became more abundant.
Will simply removing whales result in more fish being available to fisheries? In fact, in many ocean areas there are already fewer whales now than there were 100 years ago. There is no reason to expect that the removal of whales would lead to increased catches of fish, because of complex ecosystem interactions with unpredicted and often unexpected results. By far, the most effective way to improve fishery yields would be through better fisheries management as outlined by the United Nation's Food and Agricultural Organisation.
The Facts about Whales and Fish Stocks
- 1. Overfishing by humans, not whales, has been identified as a major problem for the worlds' ocean resources.
- 2. Many whales feed on krill and fish species not used by humans.
- 3. In most cases, predatory and cannibalistic fishes are greater predators of fish than are whales and other marine mammals.
- 4. Hunting whales is unlikely to provide increased catch of fish Species, because of the complexity of ecosystem interactions.
For more information contact NOAA Office of Public & Constituent Affairs,
US Department of Commerce,
14th Street & Constitution Avenue N.W.
Room 6013, Washington, DC 20230 - 0001
Back to MENU