So What About Fish?

Thus began an article in the spring 2007 issue of Ocean Conservancy magazine, and the answer has been haunting me for months. Four scientists, William Dewar and Rory Bingham at Florida State University and Mark Huntley and Meng Zhou of the Universities of Hawaii and Massachusetts, as well as other marine biologists, have started to look at ocean mixing in a whole new way. We all have learned that the turbulence of oceanic currents, as well as the forces of wind and weather, is essential for mixing the waters of the earth's seas and oceans. Without mixing, the nutrients from the ocean depths would not rise to feed the zooplankton that forms the base of the food web. Turbulence also helps in the sequestration of carbon dioxide and the breakdown of pollutants. Seas without adequate mixing are anoxic, dead, and deadly to animals whose physiology is oxygen based.

It doesn't take much to create some turbulence in the sea. If you could run a single electric cake mixer at a depth of a few kilometers, you could mix a cubic kilometer of the water around you. But until the researchers noticed what a lot of turbulence whales and fish could create, no one even considered the tremendous possibilities of “bio-turbulence." Any species of whale could accomplish quite a bit of stirring, and many, like the sperm whales, regularly swim from the surface to great depths and back. Dewar notes that there are now only about three hundred sixty thousand sperm whales, whereas once they numbered over a million. What effect has the loss of so many whales had on the mixing of nutrients in the oceans? A hundred bluefin tuna can mix twenty square kilometers of water daily. Norwegian herring, once nearly fished to extinction, but once more fairly plentiful, migrate across the Norwegian sea each spring to spawn in a single fjord. This massive school of fish moves in a band ten or twenty meters thick and as wide as the city limits of Dallas, Texas! The turbulence the herring school creates is essential to mix the very stratified waters of the Norwegian Sea and feed the plankton on which the lives of the herring and their offspring depend.

These are intriguing and exciting ideas, but nothing compared to the results of studies carried out at Saanich Inlet off the southeastern tip of Vancouver Island. There Eric Kunze and John Dower of the University of Victoria have measured the activity of euphausiids, the shrimp-like krill that are the primary food for salmon, herring and blue whales as well as many other species. The euphausiids spend the daylight hours in the deep, just above the still anoxic layer where only bacteria can thrive, but at night they swim rapidly to the surface creating turbulence of about one hundred times the daylight levels. With them come some of the nutrient products of the bacteria below. Kunze wrote in Science that such activity, ocean-wide, potentially is the dominant force in upper level mixing, and that it is the small swimming species, from tiny krill and copepods to schools of herring that generate most of the ocean’s bio-mixing. William Dewar estimates that there are three billion tons of zooplankton migrating up and down in the water column daily, producing enough turbulence to account for one half of the forces needed to mix water to the depth of a kilometer beneath the ocean's surface.

The implications of these new findings are terrifying. As humans consistently over-fish the waters, there are fewer big fish, sharks, and whales to mix the waters. But we are also taking far too many of the smaller fish, herring, mackerel, squid and others. The harvest of krill both for human and animal feed has begun. As well as robbing the seas to satisfy our protein demands, we are polluting the coastal waters with fertilizers, sewage, and herbicides, enlarging existing anoxic zones and creating huge new areas of dead water. Life on earth depends on healthy oceans. There are many ways each of us could try to heal our oceans, from the choices we make at the fish market, to refusing to buy meat and dairy products produced under industrial feedlot conditions. We can work to stop the use and abuse of chemical fertilizers and pesticides by signing petitions and writing letters. There are myriad ways we can try to help. And perhaps if enough people in the world want change, want to protect the oceans, we will become like those lively little euphausiids swimming en masse to the surface. Each of us is pretty unimportant, but together, we can make some really big waves.

-Reida Kimmel 

Tiny Farmers?

In the September 21, 2006 issue of the National Geographic, I found another question that the scientists are asking relevant to the effects of krill-created turbulence. Are the krill “tiny farmers”?

Scientists have studied the mechanical elements of the turbulence that brings algae and other organisms to the surface for schools of small fish and krill to eat. The welling up of cold water from ocean depths creates a turbulence carrying the buffet upwards where the krill and others feed. Often there is an over abundance of these small plant-like organisms and algae, that is, an abundance above what the measured upwelling, winds and tides could supply. Mark Huntley (mentioned in Reida’s piece) suggests it’s possible that the migrating krill are “stirring the pot” as a means of bringing even more dinner to the table—perhaps important farmers in the marine food chain.

-Editor