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Sharks down => Rays up => Scallops down

Posted by Coturnix on March 30, 2007
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In today’s issue of Science, there is a study showing that hunting of sharks, by eliminating the main predator of rays, leads to a decline in the ray’s – and ours – food: the scallops:

A team of Canadian and American ecologists, led by world-renowned fisheries biologist Ransom Myers at Dalhousie University, has found that overfishing the largest predatory sharks, such as the bull, great white, dusky, and hammerhead sharks, along the Atlantic Coast of the United States has led to an explosion of their ray, skate, and small shark prey species.

“With fewer sharks around, the species they prey upon — like cownose rays — have increased in numbers, and in turn, hordes of cownose rays dining on bay scallops, have wiped the scallops out,” says co-author Julia Baum of Dalhousie.

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Here is a local North Carolina angle:

Too many sharks have been killed, so they’re no longer devouring a voracious predator that feasts on bay scallops, marine researcher Charles “Pete” Peterson concludes. As a result, North Carolina’s bay scallops fishery, once worth $1 million a year, has been wiped out.

The finding, reported today in the journal Science, is evidence that harm to one creature in an ecosystem can unexpectedly injure another, Peterson said.

“The marine environment is so vast and three dimensional, there are many linkages,” he said. “There are cascading and domino effects.”

Sharks don’t eat scallops. But the top predators do feast on cownose rays — kite-shaped creatures that migrate through North Carolina waters. And the rays eat scallops, hordes of them, as they make their late-summer and early-fall travels south.

The timing of the cownose trip past North Carolina is particularly harmful to scallops, Peterson said. The rays arrive from from mid-August to mid-September. Scallops, which live about 18 months, don’t start spawning until September. So the rays eat them before they can reproduce.

Learn more about the Cownose Ray.

Craig has some more (and may write even more later so check his blog again).

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Comments

  1. #1 The Olive Ridley Crawl
    March 30, 2007

    Yeah, saw this story yesterday. It’s sad, we (at least I) learned about “Ecological Balance”, and not upsetting it in the earliest biology classes I can remember. It’s really frustrating being a scientist at times because the most basic tenets of the science are often lost when moving along to implementation of policy. The fact that sharks eat rays which eats scallops should be known to anyone who has any knowledge of the system. Instead, it takes an article in Science, of all places. Oh well, back to work.

  2. #2 Laelaps
    April 1, 2007

    A large part of the problem with sharks is that no one really knows how many there are for many species, thus making management plans difficult to implement as well as effectiveness. When I started my undergrad career as a marine science major, I asked my adviser and some of my professors how I could get involved with shark research, and their general response was “What are you going to ever do with sharks? No one studies them,” so there’s a gaping hole in our knowledge.

    The shark fisheries problem also belies an ongoing fisheries problem that goes back a lot further. Shark fisheries were encouraged by the government during the 80′s to take pressure off other collapsing fisheries, and such fishermen soon found out because sharks are big predators that take a long time to mature and breed, opening a fishery for them wasn’t going to be sustainable in the long term, the government then trying to shut down the shark fisheries they encouraged. Finning (cutting off a sharks fins and then throwing the still-living shark back into the ocean) is also an enormous problem, the economic success of the middle class in Asia making shark-fin soup (it’s believed to be an aphrodisiac and was previously only available to heads of state) creating a big demand for the soup to show status and power.

    Anyway, there’s a huge gap in our understanding of shark population ecology, and few people (if any) are doing much to give us an accurate picture. I live in New Jersey, and big sharks have historically been commonplace along the East Coast, but no one I know of is doing any work to determine how many sharks there are, where they are going, what their mortality and recruitment rates are, etc. Whatever management plans are made are going to be shots in the dark until there’s some actual data to work with. (And apologies for the extra-long comment)

  3. #3 Bruce Everiss
    April 2, 2007

    You can help in the campaign to prevent shark slaughter by signing this petition:

    http://www.petitiononline.com/SharkS/petition.html

    To: Hu Jintao president of the People�s Republic of China.

    Currently the Chinese people are eating a soup which is causing the biggest ecological disaster of our time. Supplying the demand for Shark�s Fin soup involves the death of what best estimates say are between 50 and 150 million sharks a year. This is unsustainable and will inevitably lead to all sharks becoming extinct, many species are already over 90% eradicated.
    The shark is the apex predator that keeps the whole ecology of the sea in balance and healthy. Nobody knows what the effects of their removal will be but is can be guaranteed to involve a lot of unwanted harmful outcomes.
    This petition seeks the Chinese government to ban the catching, import and sale of sharks and all shark related products.

  4. #4 Nadia
    May 31, 2009

    Hello, I am doing my pre-grade thesis in a peruvian scallop Argopecten purpuratus, I am investigation about the circadian rythm of the respiration and filtration rate.

    I would appreciatte if you can send me some further information about investigations projects of circadian rate in scallops, I am searching at internet but I am not having too much luck.

    Thank you very much.

    Nadia Balducci
    Bachellor of Biology
    PERU