On Boston’s Fishweirs and the Demise of Coral Reefs

Andrew Revkin, in response to a NY Times op-ed claiming that the coral reefs are doomed, finds some other marine ecologists who disagree. Frank Bruno states:

It is scary, but is it true? I don’t think so. I have been called a pathological optimist, but on the other hand, I’ve watched reefs change radically from the dangerous wild places I experienced as a kid in the Florida Keys, to simplified systems with few corals and fewer predators. And this is in just 30 years.

One aspect of my research is focused on documenting and understudying the degradation of coral reef ecosystems, mainly in terms of the loss of reef-building corals. …The story is more grim in the Caribbean, where there has been a decline of at least 50 percent (and probably more than 75 percent) of coral populations.

But the picture of coral loss is roughly the same globally. More recently, we’ve been working on the extent of overfishing and predator loss on Caribbean reefs. A healthy unfished reef is inhabited by top predators like sharks and grouper and total fish biomass is roughly 500 grams per square meter. Yet, the average reef has only 20 grams per square meter — obviously an extreme decrease in fish biomass.

So that aspect of Rogers Bradbury’s Op-Ed in today’s New York Times is generally accurate. The world’s coral reefs have indeed changed, are under enormous pressure, and their future is threatened.

But are they really “on a trajectory to collapse within a human generation”? No.

Is there really “no hope of saving the global coral reef ecosystem”? No, there is hope.

And is the “scientific evidence for this is compelling and unequivocal”? No, not remotely.

Back in the day, I use to be a marine biologist, so I’ve, as a dilletante, followed this literature, and I think Bruno’s take is better supported by the evidence. Part of the problem is that humans always alter ecosystems–and in a non-trivial way.

Which brings us to apparent nonsequiter of Boston’s fishweirs. A fishweir is basically a large fence that is used to trap fish, which are then caught (usually scooped out of the water), and looks something like this:

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Every year, a fishweir is reconstructed on the Boston Common (more information is available here). During the excavation and construction of Back Bay, a fishweir, thought to be about 3,700-5,200 years old, was discovered at what would today be Clarendon and Boylston streets–which then would have been a shallow marine intertidal zone. I bring up fishweirs because it’s important to realize what makes the large investment in building them useful: lots and lots of fish. You’re basically trapping fish against a fence and either spearing them or grabbing them.

For anyone who is familiar with New England salt marshes and seashores, this strategy seems ridiculous. When is the last time, in those habitats, you have seen enough fish (and minnow-sized fish don’t count) to justify this strategy? What many people don’t realize is that these habitats, until a couple of centuries ago were teeming with wildlife; in terms of productivity, these habitats are marine equivalent of Iowa farm soil. In Maine, lobster, in shallow habitats, were so plentiful, they were used to fertilize soil–and feeding lobster to servants, slaves or orphans in the 1600s was illegal (it was considered feeding people cockroaches). Ditto the fish.

Needless to say, we’ve changed those environments. Despite those changes, it’s safe to say these habitats and most of their species still exist, though many species have probably altered their behavior and physiology to compensate for human activity (e.g., cod reproduce at smaller sizes to produce offspring before being caught). On the other hand, there are habitats that we have essentially annihilated, such as the pre-European American prairie. The passenger pigeon is extinct, and the bison is a relict species.

Whether or not coral reefs will become extinct doesn’t seem to be the right question. The real issue is one of massive alteration: are a decrease in coral reef size, altering of animals (e.g., cod), and the loss of biodiversity–locally on reefs and globally by species extinction–acceptable? Will (or how many) species go the way of the bison or passenger pigeon? Will coral reef ecosystems be confined to small isolated, habitat islands? And is this good for us?

That seems a more productive way to view the problem. And Randy Olson will still have plenty of terrifying material to work with.

Bonus pictures–Here’s the location of the fishweir:

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Here’s some more information about it:

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2 Responses to On Boston’s Fishweirs and the Demise of Coral Reefs

  1. dr2chase says:

    It’s not that long ago. I’ve heard from two people who grew up in Florida that during the Depression, if you (or your friend) could throw a cast net, you would not go hungry. I remember schools of mullet when I was a kid (60s) much thicker than anything I’ve seen since, gathered in a mass near the surface of the water. And I remember buying a cast net from a guy (something Whitaker) known as “The Cast-Net King”, and he had a mullet smoker in his yard, with a sign on it saying “don’t steal fish; if you are hungry, knock on the door, I will feed you”. (First rule of cast netting: No buttons. Kind of like “no cape!” only instead of getting sucked into a jet engine, you get dragged into the water, tangled in a mess of nylon monofilament and lead weights.)

    See also: http://edis.ifas.ufl.edu/fe123

  2. joemac53 says:

    Fish weirs still exist in Nantucket Sound. They were used mostly to trap squid and menhaden. I am not sure what they pick out of them now. They were put up each spring and removed in the fall. You could be very selective about what you kept, and unwanted fish could just swim away. My junior high school science teacher tended these weirs until a few years ago.
    We used to cast-net on menhaden for chum when we were tuna fishing in the ’80s. Occasionally we would get a bluefish or two, not what you want to see at 3 AM.

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