By Ryan McGreal
Published September 15, 2006
Bright algal bloom in Gulf of St, Lawrence (Photo Credit: NASA Visible Earth)
Congratulations, humanity: in a couple of decades, we've managed to drive the world's large ocean fish to the edge of extinction.
According to a recently published study by Drs Ransom Myers and Boris Worm, scientists at Dalhousie University in Halifax, the world's populations of large ocean fish - swordfish. marlin, sharks, cod, and tuna - have been reduced by 90 percent since large-scale industrial fishing was introduced.
The authors write:
Although it is now widely accepted that single populations can be fished to low levels, this is the first analysis to show general, pronounced declines of entire communities across widely varying ecosystems.
The remaining members of these species are under such pressure from fishing that they do not grow large and often do not have the chance to reproduce.
Sharks, which existed before dinosaurs, have survived for 400 million years but are now close to extinction.
"We are in massive denial and continue to bicker over the last shrinking numbers of survivors, employing satellites and sensors to catch the last fish left," Dr Myers told the BBC.
"The last sharks are declining at a great pace and unless we reduce the number of hooks in the water by 50-60% the large sharks will go extinct - we will have no more hammerheads, no more great whites, no more large threshers.
"These species will go the way of the dinosaurs unless we take worldwide action to preserve the diversity in the marine ecosystem."
Even when they are not menaced by factory fishing, the world's ocean vertebrates are under pressure from the steady elimination of food sources as human activity changes the chemical composition of the sea.
Industrial society is overdosing the oceans with basic nutrients - the nitrogen, carbon, iron and phosphorous compounds that curl out of smokestacks and tailpipes, wash into the sea from fertilized lawns and cropland, seep out of septic tanks and gush from sewer pipes.
Modern industry and agriculture produce more fixed nitrogen - fertilizer, essentially - than all natural processes on land. Millions of tons of carbon dioxide and nitrogen oxide, produced by burning fossil fuels, enter the ocean every day.
These pollutants feed excessive growth of harmful algae and bacteria.
At the same time, overfishing and destruction of wetlands have diminished the competing sea life and natural buffers that once held the microbes and weeds in check.
In the place of heroic fish we get what one scientist called "the rise of slime" - vast blooms of algae and cyanobacteria, toxic fireweed, swarms of jellyfish, and, notably, the steady destruction of coral reefs and kelp beds.
Jeremy Jackson, an ocean scientist studying the phenomenon, warns against the assumption that the oceans are big enough to absorb human waste. The scale of human activity is so massive that the changes we're causing are global and permanent.
Jackson uses a homespun analogy to illustrate what is happening. The world's 6 billion inhabitants, he says, have failed to follow a homeowner's rule of thumb: Be careful what you dump in the swimming pool, and make sure the filter is working.
"We're pushing the oceans back to the dawn of evolution," Jackson said, "a half-billion years ago when the oceans were ruled by jellyfish and bacteria."
Daniel Pauly, a fisheries scientist at the University of British Columbia, summarizes the direction we're taking the world's oceans; "My kids will tell their children: Eat your jellyfish."
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