Oceans as Barren Deserts

Many moons ago, I noted this about Boston’s annual display of a fish weir, which is a glorified fence used to catch fish–yes, a fence:

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).

Some years later, some asshole with a blog noted:

That’s right, intertidal marine life a few centuries ago was so plentiful, you could basically scoop it out of the water with baskets…

No one alive truly understands what we have done to oceans–that they could be so teeming with life is completely alien. There simply isn’t any place where one can find this concentration of marine organisms (unless you’re in the middle of a school of fish). We have created a barren desert.

Ed Yong describes what whaling has done to the oceans (boldface mine):

In just six decades, roughly the life span of a blue whale, humans took the blue-whale population down from 360,000 to just 1,000. In one century, whalers killed at least 2 million baleen whales, which together weighed twice as much as all the wild mammals on Earth today.

All those missing whales left behind an enormous amount of uneaten food. In a new study, the Stanford ecologist Matthew Savoca and his colleagues have, for the first time, accurately estimated just how much. They calculated that before industrial whaling, these creatures would have consumed about 430 million metric tons of krill—small, shrimplike animals—every year. That’s twice as much as all the krill that now exist, and twice as much by weight as all the fish that today’s fisheries catch annually. But whales, despite their astronomical appetite, didn’t deplete the oceans in the way that humans now do. Their iron-rich poop acted like manure, fertilizing otherwise impoverished waters and seeding the base of the rich food webs that they then gorged upon. When the whales were killed, those food webs collapsed, turning seas that were once rain forest–like in their richness into marine deserts

Surely, then, the mass slaughter of whales must have created a paradise for their prey? After industrial-era whalers killed off these giants, about 380 million metric tons of krill would have gone uneaten every year. In the 1970s, many scientists assumed that the former whaling grounds would become a krilltopia, but instead, later studies showed that krill numbers had plummeted by more than 80 percent.

The explanation for this paradox involves iron, a mineral that all living things need in small amounts. The north Atlantic Ocean gets iron from dust that blows over from the Sahara. But in the Southern Ocean, where ice cloaks the land, iron is scarcer. Much of it is locked inside the bodies of krill and other animals. Whales unlock that iron when they eat, and release it when they poop. The defecated iron then stimulates the growth of tiny phytoplankton, which in turn feed the krill, which in turn feed the whales, and so on.

There’s a pilot experiments to see if we could fix this–and I have no idea if this will work (or create other problems):

There are more whales now than there were even a few years ago—in early 2020, scientists rejoiced when they spotted 58 blue whales in sub-Antarctic waters where mere handfuls of the animals had been seen in years prior. But that number is still depressingly low. “You can’t bring back the whales until you bring back their food,” Savoca said. And he thinks he knows how to do that…

The team plans to propose a small and carefully controlled experiment to test the effects of iron fertilization on the whales’ food webs. The mere idea of that “is going to be shocking to some people,” Savoca admitted. Scientists and advocacy groups alike have fiercely opposed past iron-addition experiments, over concerns that for-profit companies would patent and commercialize the technology and that the extra iron would trigger blooms of toxic algae.

But with Savoca’s new estimates, “we now have a much better idea of exactly the quantity of iron that whales were recycling in the system and how much to add back so we don’t get bad effects,” he said. His goal isn’t to do something strange and unnatural but to effectively act as a surrogate defecator, briefly playing the role that whales did before they were hunted to near extinction. These creatures would still face many challenges—ship strikes, noise pollution, entangling fishing gear, pollutants—but at least food supplies would tilt in their favor.

We have to do something. Maybe this will work.

This entry was posted in Ecology, Environment, Fish. Bookmark the permalink.

Leave a Reply