The Biggest Die First

Large swordfish on deck during long-lining operations (photo by Derke Snodgrass via NOAA Photo Library)
Large swordfish on deck during long-lining operations (photo by Derke Snodgrass from NOAA Photo Library)

It happened to land animals. Now it’s happening in the ocean.  The biggest die first.

Based on Earth’s current extinction rate of 1,000 times the normal background rate (predicted to become 10 times worse) scientists believe we’re at the start of the sixth mass extinction.

Stanford geoscientist Jonathan Payne wondered if the traits of extinct marine animals could predict the likelihood of extinction in today’s ocean organisms. For mollusks and vertebrates Payne and his colleagues compared ecological traits such as habitat preference and body size in past extinct and present threatened genera (genus: one level above species).  The results were surprising.

In past extinctions habitat preference was a good predictor that an animal would disappear.  That’s not the case now. In this era, the best predictor of future extinction is large body size.

The difference is us.  Human hunting pressure is driving ocean extinction.  Our demand for seafood is high (there are billions of us to feed) and we’ve become very efficient at capturing the largest fish.  Highly migratory predators like the Pacific bluefin tuna have declined precipitously.

We’ve seen this before.  At the end of the Ice Age, as human population expanded across the globe, the megafauna simultaneously went extinct.  It’s now known that sabretooth tigers, giant armadillos and woolly mammoths disappeared due to human hunting.

Woolly mammoth statue in the Royal BC Museum, Victoria, BC, Canada (photo from Wikimedia Commons)
Woolly mammoth statue in the Royal BC Museum, Victoria, BC, Canada (photo from Wikimedia Commons)

We humans are successful because we make tools and hunt cooperatively.  Of course we kill the largest prey first. One large animal feeds more people.

Unfortunately we don’t know when to stop.

Read more about Payne’s study here at Science Daily.

(photo of swordfish from NOAA Photo Library. photo of woolly mammoth statue in Royal BC Museum, Victoria, Canada via Wikimedia Commons. Click on the images to see the originals)

p.s. A word about the swordfish pictured above:  Swordfish are highly migratory predators whose population is in danger in many oceans around the world.  In 1998 the North Atlantic population dropped so low that fishing was suspended.  A 2009 international assessment of North Atlantic swordfish showed they had recovered in U.S. fishing areas, so fishing resumed.  Note: The fishermen who lost their lives aboard the Andrea Gail in The Perfect Storm were longline fishing for swordfish.

One thought on “The Biggest Die First

  1. I would say most scientists know we are in the sixth mass extinction. It is caused by humans, but not from one simple source. Habitat loss and destruction have affected many species, causing populations to become isolated and restricting both their migratory movements and dispersal. Over fishing certainly impacts many species of fish, but so does rising sea temperatures. And yes, the earth experiences temperature fluctuations normally, but this is happening faster than at any other time. There are now an estimated 7.4 billion humans on the earth, and scientists think the earth can sustain about 7 billion (referred to as carrying capacity). How can we have more people on the earth than it can sustain? Because carrying capacity includes sustainability in its model. Currently we are using more fossil fuels than can be created, it is not sustainable. Food production does not meet everyone’s needs, and with increasing population there is less space to grow food. It goes on and on….So, enjoy nature while you can, it might not be there for your grandchildren to enjoy. Scientists have been sounding the alarm for years now, have you heard?

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