Oceans may run out of fish population in 50 years

Oceans may run out of fish population in 50 years

An article in the November 3, 2006, issue of Science has drawn enormous media attention. Not surprisingly. The article-- Impacts of Biodiversity Loss on Ocean Ecosystem Services-- talks of all the oceans running out of fish by the next 50 years or so. The day the article appeared, the New York Times had its quote of the day from this article: "When humans get into trouble they are quick to change their ways, we still have rhinos and tigers and elephants because we saw a clear trend that was going down and we changed it. We have to do the same in the oceans." All the hype notwithstanding, comparing trends in fish population, which are mired in uncertainties, with much more reliable trends in population dynamics of the largest mammals on land, does make one sigh in disbelief.

The twelve ecologists and two economists from research institutes in the us, Canada, the uk and Sweden, who have contributed to the study say that the article is based on a four-year analysis, believed to be the first to examine all existing data on ocean species and ecosystems.

According to Boris Worm of Dalhousie University, Canada--the study's lead author--the scientists extracted all data on fish and invertebrate catches from 1950 to 2003 within all 64 large marine ecosystems worldwide that produced 83 per cent of global fisheries yields over the past 50 years.

In an interview, Worm said, "We looked at absolutely everything--fish, shellfish, invertebrates, everything that people consume that comes from the ocean." The researchers found that 29 per cent of species had been fished so heavily or were so affected by pollution or habitat loss that they were down to 10 per cent of previous levels.

However, the names of the species under study are not mentioned in the Science article. We also do not know what percentage of global marine fish production these species constitute. According to Worm and his colleagues, the loss of biodiversity "results in an acceleration of environmental decay", and further loss of fish. The New York Times reports that Worm and his team analysed the data and extrapolated them into the future "to see where it ends at 100 per cent collapse". The 12 economists and the two ecologists arrived at the year 2048.

That bad? Steve Murawski, chief scientist of the Fisheries Service of the National Oceanic and Atmospheric Administration, us, has told the New York Times that the researchers' prediction of a major global collapse did not gibe with trends that they see in the us. He says his organisation considers only 20 percent of the us stocks it monitors to be overfished and that the fishery situation in American waters was improving. This, however, was not the case in relation to fish stocks of developing countries, he surmised.

The total fish species richness in 64 Larger Marine Ecosystems (lmes) discussed in the article--they have produced 83 per cent of global fisheries yields in the past 50 years--shows that such marine ecosystems in the tropical belt, including the Arabian Sea and the Bay of Bengal, are in much better health than their counterparts in the temperate world. The richest in biodiversity, for example, is the South China Sea. This is in spite of nationally recognised overfishing pressures in the largest marine fish producing country, China, and in other Asian countries. The worst-case scenarios include the Northern Atlantic, especially waters of Atlantic Canada, and the Mediterranean.

Cause and effect Worm has acknowledged that most of the conclusions drawn by the study is based on correlation--and not cause and effect analyses. But that hasn't precluded him from claiming that a number of steps could help turn things around: reduction of bycatch, setting up marine reserves and decreasing pressures of overfishing and banning destructive fishing in the most sensitive habitats (ban on deep sea trawling). Can a study based on correlation make such claims? Considering the complexity of marine ecosystem dynamics and poor data on fish production, it is worth questioning the quantitative techniques employed by Worm et al to draw inferences that have serious policy implications.

Sebastian J Mathew is with the International Collective in Support of Fishworkers, Chennai 12jav.net12jav.net