Tuesday, July 15, 2008

Sharks and Shellfish: a common thread

I was reading about two seemingly disparate animals: sharks and shellfish. And I came to realize there was a common thread to the life-threatening situations these animals are facing.

A recent report in the Norwegian scientific journal, Oikos, analyzed the impact on changes in seal predation behavior if the shark populations that preyed on the seals declined ("Do shark declines create fear-released systems?"). Pretty heady stuff, but through the researchers' computer models it was theorized that there could be major shifts in diets from shallower prey like herring to deeper water prey like pollock - where local sharks frequent, when the decline in shark populations has removed an element of fear that dictates a good measure of the seal's hunting behavior. Bottom line was that a decline in shark populations could produce a more significant change in the predator-prey hierarchy relationship than previously thought.

With shellfish, scientists are seeing an impact of warmer waters on various species that is producing population declines from deadly bacteria, among other factors. Oyster beds along the west coast of the U.S. are now seeing the effect (read recent article). The east coast has seen this effect, too. A platter full of shucked oysters may not be your cup of tea (it's not mine), but as filter feeders, shellfish play a critical role in maintaining water quality. When shellfish populations whither, bacteria and various types of algae explode and push out a wide range of sealife through water degradation and loss of habitat.

So, what's the connection? One is that both of these situations represent the domino effect that occurs within any complex marine eco-system. For every action, there is a reaction - sometimes a very severe or unexpected one. Another connection is that these are basically man-made problems - over-fishing and global warming - and will have an effect on commercial operations that involve these animals. So our actions come back to haunt us.

Certain marine issues can gain more traction and get more media attention or public sympathy and support. But in the end, we need to consider the overall complexity of this ecological jigsaw puzzle we call the oceans and give every issue its due.

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