Overfishing Dangerously Depleting Ocean Life
Filed under: News & Resources,Understanding
Southern Right Whale / Photograph by David Doubilet
From The Brunei Times
By Stephen Leahy
UXBRIDGE, CANADA
IMAGINE large pods of mighty blue whales and orcas darkening the waters off Cornwall, England, while closer to shore blue sharks and thresher sharks chase herds of harbour porpoise and dolphins.
Pure fantasy? No, in fact that extraordinary abundance of marine life off the English coast was the norm for oceans around the world not so long ago, researchers have now documented.
And then humans began to mine the seas of anything worth eating.
“The impact of fishing over the centuries is far larger than anyone thought,” said Poul Holm, a professor at Trinity College in Dublin and global chair of the History of Marine Animals Population (HMAP) project, which is part of the 10-year Census of Marine Life.
While many valuable species have been fished out in recent years, that has been happening for hundreds of years around the world, according to nine years of research by hundreds of experts.
“In looking back 500 to 2,000 years ago, you get a real sense of the impacts of fishing and the cascading affects on marine ecosystems, some of which may be beyond recovery,” Holm said.
“Humans have fundamentally changed ocean ecosystems,” said Andy Rosenberg of the University of New Hampshire.
“But the oceans can be very much more productive in the future with proper management,” Rosenberg said in an interview. “If we fish less now, we can get more in the future.”
It is vital to understand how the oceans and fish populations have changed over hundreds of years so that they can be properly managed for the future. “Right now fisheries management relies on 20 years of history or less,” he said.
That means current efforts to rebuild dwindling tuna stocks target the stock levels of the 1990s, which are likely far too low for real recovery.
“When it comes to marine life, in many cases we’re only just starting to fully realise what the planet once had,” said Ian Poiner, chair of the Census of Marine Life Scientific Steering Committee.
“The insights emerging from this research of the past provide a new context for contemporary ocean management,” he said.
History has powerful lessons to teach us about our relationship with the oceans. And for the first time, a global picture is emerging from diverse sources as old ship logs, literary texts, tax accounts, newly translated legal documents and even mounted trophies.
Once the oceans were filled fish of such sizes, abundance and distribution in ages past that they stagger modern imaginations.
And the seas off Cornwall in the 1600-1700s did in fact teem with sharks and whales along with many other fish and mammal species, said Holm. “I think that changes our whole sense of history about the place,” he said.
Analyses of scientifically-dated fish remains and historical data reveal that the size of freshwater fish caught by Europeans started shrinking in medieval times. At about the same time, other researchers show a shift from eating locally-caught freshwater to marine fish species.
Maria Lucia De Nicolo of the Universita di Bologna, meanwhile, has established that new fishing boats and equipment invented in the 1500s made it possible to venture from coastal to deep sea fishing. The real revolution in marine fishing, she said, happened in the mid-1600s when pairs of boats began dragging a net.
Less than 200 years later, in a serial exploitation pattern replicated around the world, fish stocks begin to collapse. Years of overfishing followed by extreme weather collapsed the European herring fishery in the 1800s. Then, the jellyfish that herring had preyed upon flourished, seriously altering the food web.
Perhaps the best documented decimation is New Zealand’s southern right whale. Analysis of over 150 whaling logbooks and other records led researchers to say with 95 per cent statistical confidence that the population numbered between 22,000 and 32,000 in the early 1800s before commercial whaling began. By 1925, perhaps as few as 25 reproductive females survived.
Today, a remnant hopefully recovering of 1,000 animals is being studied around sub-Antarctic islands south of New Zealand.
“These findings point up the need to re-examine the role southern right whales once played both as a grazer of zooplankton and prey, especially during calving close inshore, for killer whales and great white sharks,” said Alison MacDiarmid, a New Zealand government scientist who headed the study.
New Zealand and Australia are now using this far more complete historical record their conservation management said Holm. When the HMAP project is completed at the end of 2010, the hope is that both fisheries and marine conservation managers will use this data as their new baselines of what the oceans were like and also to better identify what the real drivers of change have been.
“If we continue to proceed as in the past we’ll be in deep trouble,” MacDiarmid said. “Governments have to realise that fisheries management targets can’t only be about profits.” IPS
