The World's last major "Wild" food resource is in jeopardy. That is the conclusion of an article entitled "Fishing down marine food webs," which was published last month in the journal Science. Here Jennifer English surveys the main findings of that article and interviews Dr. Daniel Pauly the article's senior author. (For further information and links, see References.)

March 16, 1998: Events such as the collapse of the Peruvian anchovy fishery in 1971, and the collapse of North Atlantic cod fishery in 1991 make it clear that the world’s last major "wild" food source is in jeopardy. Unless radical changes in fisheries management occur, the diversity of ocean life will be greatly impoverished. For the fishing industry, the oceans will become aquatic deserts offering little to harvest beside jellyfish and lanternfish.

Such is the conclusion of the article "Fishing Down Marine Food Webs," published last month in Science, the journal of the American Association for the Advancement of Science, by a group including scientists from the University of British Columbia and the International Center for Living Aquatic Resources Management (ICLARM) in the Philippines (1).

In their study, the scientists analyzed United Nations Food and Agricultural Organization fish catch data against food web models (2) to show how, since the 1950’s, global fish harvests have shifted down the food web away from species of higher trophic (food web) level (predators such as halibut and tuna) to species of lower trophic level (plankton-eaters such as anchovies). This shift has occurred as populations of predator fish have been decimated by over-fishing and fishers have been forced to harvest what is left, species of the predators’ prey.

The study demonstrated this shift by means of a scale which assigns top predators such as killer whales a trophic value of 5.0, tuna and cod a value of 4.0, and species at the bottom of the food web, like anchovies, a value of 2.0. Although the study acknowledges that some of the catch data from the Southern Hemisphere may be unreliable, the general trend is evident. Since 1950, the average trophic value of fish caught dropped from 3.4 to 3.1 in oceans and 3.0 to 2.8 in freshwater. The largest decline was off the Eastern coast of Canada and the US where the level has dropped from 3.4 to 2.9.

Alarmingly, this slide has not been accompanied by larger catches. This is contrary to expectation. Normally, as one moves down a food web, biomass increases. Instead, fish catches have stagnated as fishers have moved from top predators to species at lower trophic levels. One reason for this effect is that once a top predator has been depleted or exterminated by fishing, alternative predators, which are of no commercial value, thrive in the absence of competition and thus deplete the biomass of prey species at lower trophic levels.

The Science magazine article shows how this pattern is overlooked in present day fishing management strategies that place moratoriums on the harvest of individual species, such as cod in Atlantic Canada. Reliance on Moratoriums on the harvest of particular species is ineffective if the food source of the protected species is being depleted either by fishers or by alternative predators. To prevent total species collapse, the study suggests, "fisheries management will have to emphasize the rebuilding of fish populations embedded within functional food webs..." (1) instead of focussing on the health of one particular commercially harvested species. This broader approach to conservation could be accomplished with the implementation of more "no-take" Marine Protected Areas (MPAs).

Dr. Pauly, senior author of the Science article discussed above, answers questions about the global fisheries crisis and the concept of "no-take" areas:

naturalSCIENCE: How does over-fishing compare in its impact on aquatic ecosystems to other disruptions such as pollution and climatic aberrations such as El Niño?

Dr. Pauly: On a global basis there is no environmental factor affecting marine communities (i.e., removing fish and bottom habitat) that is comparable to the fisheries in impact. El Niño and other local effects modify the range and recruitment of various species, but do not remove entire communities, i.e., they do not cause species to become extirpated throughout most of their range as the fisheries do. After all, fisheries are meant to kill fish. It is the public who believes that the 'environment' disrupts fish resources, and it is a useful smokescreen for the industry.

naturalSCIENCE: You think it unjustifiable, then, to blame seals (See Below) for the slow recovery of Canada's Atlantic cod fishery?

Dr. Pauly: It is a joke to blame seals for the slow recovery of cod stocks. Humans and seals coexisted for hundreds of years around Newfoundland, and the cod fishery was not much affected by seals or the environment. Obviously, the seal consumption of cod will look large relative to the total cod stock if the cod biomass is reduced to abysmally low levels by the fishery.

naturalSCIENCE: What would be the best way to implement the "no-take" Marine Protected Areas suggested in your report?

Dr. Pauly: The best way of implementation would be to involve the public at large in a debate about the resource. After all the resource doesn’t belong to the industry, but to all citizens. The alternative to setting up Marine Protection Areas (MPAs) is to gradually lose all larger fish species presently exploited.

naturalSCIENCE: How much more of the oceans would have to be put aside in addition to the 1% that is currently protected?

Dr. Pauly: About 30-50% of the oceans would have to be put aside in MPAs. There is much research being done to determine what would be the optimum properties of such sites.

naturalSCIENCE: What role do you see aquaculture having in terms of controlling fish harvests, and how does intensive fish-farming affect species diversity?

Dr. Pauly: Aquaculture has no bearing on the control of fish harvests. It may actually be deleterious to fisheries management. With the growth of the fish-farming industry, wild fisheries management may be seen as superfluous. In terms of species diversity, in the North Atlantic, salmon farming has a very negative effect on the genetics of wild salmon.

naturalSCIENCE: To what extent are Western intensive fishing techniques used in the developing world, and, if "no-take" areas are needed, do you foresee resistance by developing countries similar to that shown in negotiations over reduction of carbon dioxide emissions?

Dr. Pauly: Western intensive fishing techniques now dominate in the developing world. Some of the first "no-take" MPAs were implemented in developing countries in the Caribbean and the Philippines, with very positive results. These experiences were worthwhile because the MPAs actually increase fish catches in the adjacent areas.

Dr. Daniel Pauly is currently a Professor at the UBC Fisheries Centre, Vancouver, Canada and is also the Principal Science Adviser for the International Centre for Living Aquatic Resource Management (ICLARM), Manila, Philippines. He has taught on five continents in four languages about fish population dynamics. He has authored, co-authored and edited over 300 scientific articles, reports and books.


What Is the Case for Killing Seals?

There is little published scientific evidence to justify the government-subsidized seal hunt as a means of restoring cod stocks in Canadian waters off the coast of Nova Scotia and Newfoundland. Such was the view of 97 scientists from 15 countries who signed a petition opposing the hunt at the Eleventh Biennial Conference on the Biology of Marine Mammals in Orlando, FL (14-18 Dec. 1995). The petition stated:

As professionals in the field of marine mammal biology we disagree with the Canadian government's statement that North Atlantic seals are a 'conservation problem'. All scientific efforts to find an effect of seal predation on Canadian groundfish stocks have failed to show any impact. Overfishing remains the only scientifically demonstrated conservation problem related to the fish stock collapse. If fishing closures continue, the indicates that the stocks will recover, and killing seals will not speed that process. (International Marine Mammal Association) (3)

Despite a lack of evidence, this year’s hunting quota in Canada is 275,000 seals. Observers report that the actual number of seals killed, including those whose carcasses are not recovered, may exceed the quota by as much as a factor of four (4). This greatly exceeds the 170,000 seals that Canada's Department of Fisheries and Oceans estimates can be killed in a year without depleting the population (5).

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