(Painting by Barry Kent MacKay)
To understand why cormorants cannot eliminate fish, one must have at least a very elementary understanding of how all creatures exist. Put simply, we all need to have food that can be converted by our bodies into tissue, energy and warmth. This conversion process is called metabolism, and is a two-part process. Food provides us with the means to create cells and tissues and organs and fats. But the energy we expand in order to acquire food consumes our physical being.
Put simply, what we use up in producing energy and body mass must be balanced by what we consume. If we eat more than we need we grow fat, if we consume less than we need we grow thin. If we continue to eat less than we need we not only become thinner, we ultimately sicken and die.
Matter, heat and energy are interchangeable. The energy that goes into the building and maintenance of healthy bodies, to keeping us warm and allowing us to move, derives from the food we eat. The energy that it takes to read these words is much less than it takes to run a marathon or work out at the gym, but whatever we do, we have to be sure that we have the fuel with which to do it. Even sleep takes some degree of energy.
But there is one massive difference between us, and all other species. That difference is technology. We don’t use very much of our own metabolic energy to obtain food. Instead, we use energy derived from other sources. The food a deer consumes must provide all the deer’s needs, from what is required to grow and maintain its body and bodily functions, to the energy it takes to search for food, avoid predators, breed, keep warm in cold weather, find shade or cover, or anything and everything else it does as a function of being and staying alive. The wolf who hunts the deer has the same limitations. The energy spent obtaining food must be balanced by the energy derived from the food.
Now consider the human in pursuit of the same food as the wolf. He too uses energy — to drive to the hunt site, to climb to his deer stand, to load his gun, to squeeze the trigger — but all of this is made possible by energy sources that do not come from his body, but from fossil fuels, from hydroelectric power, or perhaps from other energy sources that exist independently of what he derived from his food. Enormous amounts of energy that have nothing to do with his body’s metabolism, and may be generated and spent thousands of miles away, are required to put him in a position where, with the squeeze of a finger, he can kill a deer, and if he does not, no matter — technology provides him with other food sources.
A few wildlife species have learned to use the most simplistic tools — a small bird found only in the Galapagos Islands can use a stick to probe for insects, for instance, and so can a species of crow found on New Caledonia, and so can the chimpanzee — but not one other species has access to complex tools and the outside energy sources it takes to provide them. A fisherman without a boat and engine, a synthetic rod and reel, perhaps a fish finder, and don’t forget clothing, a cooler, a wristwatch, a car, a choice of hooks and lures, a landing net, perhaps eyeglasses — countless mechanically produced aids whose presence cost him no caloric output — uses far more energy than the energy he derives from the fish he catches and consumes.
The cook may give little thought to the energy that manufactured the can he opens in order to access the soup he is preparing for lunch, not to mention the energy expended by farm machinery to grow the vegetables in the soup, nor to build and run the machinery that moves those vegetables to the factory where more machinery built and using more energy prepares the ingredients to go into cans built and transported.
That transportation uses still more machinery, said machinery representing still more energy both to be made and to function in order to bring the various components together at the factory. Then more energy is required to ship the products in containers that used still more energy to be made and transported to the factory so that they can be sent to a store made from still more machinery built and maintained using still more energy, and so on through a long chain that must occur before the cook ever enters the picture. Even when the can of soup is bought and transported to the kitchen it must be heated on a manufactured stove run on still more energy, additional to what went into the metal from which it is made being taken from the ground, shipped and turned into a stove that is shipped to a store and then to the kitchen, the soup is poured into a bowl and eaten with a spoon that have consumed more energy to be built and shipped, all so a simple lunch can be served. Of course to dump the soup into a pot, and, once heated, into a bowl, and to lift the spoon from bowl to mouth does require metabolic energy, but it is a fraction of the amount of energy from non-metabolic sources that allowed the soup to be there in the first place. And we won’t discuss the dishwashing that follows, or the disposal of the tin can or the manufacture of the soup bowl.
No other species has that option to access energies derived mostly from fossil fuels, but also, to varying degrees, from atomic power, wind and solar power, water-driven turbines, battery power or even tidal or geothermal power. The late John A. Livingston, Canadian naturalist-author, referred to technology as a “prosthesis,” a contrivance that humans have come to depend upon for their survival. He provocatively argued that humans were the first species to domesticate themselves. Most people are not really aware of just how much they depend on technology, and the expenditure of energies that do not derive from their own bodies. It is all taken for granted.
Now consider the cormorant. The energy that she needs to expend in order to survive must be balanced by the energy derived by the food consumed. That is true of every species but humans. Compared to humans, the chain of energy expenditure is relatively simple. The cormorant must swim underwater, pushing against the inertia of the water to drive her body with enough speed to overcome the fish, while holding her breath (oxygen being essential for metabolism to occur and birds, like us, get their oxygen from air) and maintaining all bodily functions. During the nesting season the amount of fish captured must meet her increased needs to produce eggs, and later to feed her young. Not all of the fish is converted into what the body needs, with the remainder ejected as excreta that contains concentrated nutrients often transferred from water to land.
Let us imagine a situation where cormorants really could eat all the fish. Visualize a swimming pool, stocked with 200 or so fish, each maybe 4 to 5 inches long, thus a perfect size for cormorants to swallow. Let us further pretend that these fish are sluggish in movement, thus easy to catch.
Now let us imagine two hungry cormorants placed in the pool. They must eat to survive, obviously, but what would happen if the only place they could eat was in the pool? At first the cormorants would do well, there being 200 fish distributed in the pool. It would be relatively easy to catch the first ones as none would be too far away if they were evenly distributed. If concentrated in one part of the pool they’d also be easy to catch. As the number of fish went down the cormorants would have to expend still more energy to catch each fish because each fish would have more space to flee.
Eventually one of two things would happen: In Scenario One the cormorants would eventually catch all the fish and then starve, because that was the only place where they could eat (and we are imagining fish who are conveniently sluggish in movement, so ultimately all could be caught). That would mean no fish and thus, soon after, no cormorants.
Scenario Two requires that we imagine the fish not to be so sluggish and the pool larger. The fish are fast-moving, and whoever owns the pool makes sure that they have lots to eat so that they maintain high energy levels.
In this state of affairs as the number of fish decreases, the amount of energy needed to catch the next one would increase, as in the first scenario. The difference is that in this imaginary situation there would eventually be so few fish that the amount of energy required to catch them would be more than they provided when caught and consumed, and the cormorants, having reached that point of diminishing returns, would die. There might be very few fish, but that would be a temporary condition. Fish produce lots of eggs, lots of young — some species producing hundred, even thousands — and since the cormorants would be gone, there would be a greatly increased survival of young fish so long as the pool’s owner keeps the fish food coming. Eventually, even with unlimited food, there would be so many fish that there wouldn’t be enough water to sustain them and they, too, might become extinct ... at least in the pool.
NEXT » Back in the Real World
Cormorants: Food Chains and Basic Ecological Principles
The Alewife, Alien Salmon and Trout, and the Double-Crested Cormorant
The Round Goby
The Difference Between Science and Management
The Agricultural Subsidy
The Missing Predator Argument
Semi-Science and Wildlife Management
So ... What Do Real Scientists Say?