Fisheries and the Control of Marine Mammal PopulationsWith human population growth placing increasing pressure on food supplies, concerns surrounding fisheries yields have become as much humanitarian as they are economic in nature. Thus, marine mammals that feed on fish are sometimes perceived as competitors that must be controlled to ensure humans a bigger piece of the pie. Fishermen are concerned about what possible impacts seals and whales may have on commercial fish stocks. Meanwhile, whaling nations use the argument that marine mammals are competitors to justify their hunting activities. But what role do marine mammals really play in the reduction of fish stocks? Does the culling of marine mammals automatically lead greater fisheries yields?With human population growth placing increasing pressure on food supplies, concerns surrounding fisheries yields have become as much humanitarian as they are economic in nature. Thus, marine mammals that feed on fish are sometimes perceived as competitors that must be controlled to ensure humans a bigger piece of the pie. Fishermen are concerned about what possible impacts seals and whales may have on commercial fish stocks. Meanwhile, whaling nations use the argument that marine mammals are competitors to justify their hunting activities. But what role do marine mammals really play in the reduction of fish stocks? Does the culling of marine mammals automatically to lead greater fisheries yields? Are Marine Mammals Truly Responsible for Declining Fish Stocks?Take the case of the collapse of the cod fishery in the Gulf of St. Lawrence. Although government and fishermen are at odds as to the principal cause of this decline, they do agree that the abundance of seals in the Gulf of St. Lawrence may inhibit the recovery of codfish stocks. Is this an irrefutable scientific fact or simply another example of the scapegoat syndrome? Will reducing harp seal and grey seal populations really reverse the trend and guarantee a renewed proliferation of codfish? The question is still open to debate. Caution is AdvisedSeals were also considered to be the culprits in the case of the decline of the Atlantic salmon. Yet, studies have demonstrated that seals rarely eat salmon. Only one of the 700 grey seal stomachs harvested near Anticosti Island contained salmon; Atlantic salmon are considered abundant in the Anticosti area. Furthermore, the examination of 9000 harp seal stomachs over the past 30 years has revealed the presence of but one salmon. Seals do not appear to play a major role in the very complex mystery of the Atlantic salmon decline. A Historical Reminder: The Case of the St. Lawrence Beluga WhalesSt. Lawrence beluga whales were accused of being responsible for the scarcity of cod and salmon in the 1920s. In response, the government distributed rifles and ammunition, offering bonuses to fishermen to kill as many beluga whales as possible. Eight years after this system was put in place, Dr. Vladykov carried out a study on the beluga whale’s diet. He discovered that beluga whales fed mostly on species of no commercial value, such as American sand lance, capelin, sculpin, clam worms, clams, squid, octopus and various crustaceans. Fewer Marine Mammals, More Fish?Be that as it may, if we still wish to guarantee humans a more substantial portion of fish stocks, is the culling of marine mammal populations an efficient way of going about it? The argument in favour of this method appears quite simple: reduce the size of a predator population and you will increase the population of a commercially interesting species (species 1), thus increasing catches of this same species. However, if we were to add another species of fish (species 2) to this reasoning—a species that is simultaneously prey for the targeted predator and a predator of species 1—the situation becomes more complex. While the reduction of the number of predators will be favourable for the population of species 1, it will also be favourable for the species 2 population. The increase of the species 2 population could then translate into increased predatory pressure on species 1! It really is quite difficult to predict whether the population of the prized fish (species 1) will increase or decrease in response to the decline of one of its predators. Moreover this model is but a simplified version of reality. There are more than two vectors between the targeted predator and the prized prey; there are thousands of them. The notion of time must also be included to render such a model more realistic. Given that certain vectors are longer than others, it is possible to obtain the desired effect in the short term, only to observe the opposite effect later on. Despite prevalent uncertainty, pressure remains strong to put the blame on marine mammals for declining fish stocks. Are they being targeted because they are the most visible predators? Or could it be because they are already considered a pest due to the problem of accidental entanglement in fishing gear? The coming years will be crucial for whaling. Whatever the conflict, everyone agrees that we must avoid repeating past errors. How will we meet this challenge? It is likely crucial that we fully understand the debate and consider cultural differences. Fewer Fish, Fewer Marine Mammals?What would happen if we were to invert the question? How does the fishery affect marine mammals? Are there cases where humans entered into competition with marine mammals and ended up impoverishing their food resources? Furthermore, what would happen if we were to lift the ban on the harvesting of species that are at the base of the food chain? What would be the consequences on bird, marine mammal and fish populations if the krill fishery—krill being a species upon which a large number of predators depend—were to expand? Contrary to natural predators, humans have access to powerful technology and a wide range of alternative resources. Fisheries may have a major impact on predator populations, not to mention entire ecosystems. With this in mind, the best possible solutions appear to be better management of what is harvested from the natural world and a halt to excessive exploitation of the marine environment, as much to ensure the continuity of fish stocks as to protect marine ecosystems. I want to know more The United Nations Environmental Programme:
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