11 Mar 2013: Essay
Counting Species: What It Says
About Human Toll on Wildlife
By analyzing mitochondrial DNA, scientists now can make more accurate estimates of the numbers of individual species that existed centuries ago. What does it tell us about our impact on the natural world and about our own future?
There is one good thing to be said about 19th-century whaling. It produced a cache of biological data that is unparalleled for its time. Whaling — largely an American industry then — was a truly global scourge, profitable, destructive, obscene, and bloody beyond belief. Yet when it came to the details of the kill — time, location, species — whaling captains were often punctilious, because being punctilious about the ship’s log has always been part of a captain’s duty.
The same year Moby Dick
was published, 1851, the great oceanographer Matthew Maury published a global “Whale Chart
,” showing the distribution of whale species based on evidence gathered from whaling logs. Maury’s work has been expanded more than once over the years, culminating in a recent study called “Spatial and Seasonal Distribution of American Whaling and Whales in the Age of Sail
By their nature, though, even the earliest whaling logs can’t answer a vital question: How many whales were there before large-scale whaling began?
How many humpback whales were there before we thought to count them?
The answer matters for many reasons. The International Whaling Commission (IWC) uses estimates of pre-whaling populations as a basis for regulating whaling. And knowing the pre-whaling numbers is a way of measuring the recovery of whale species. For instance, there are some 17,700 North Atlantic humpbacks now, well up from the mid-twentieth century when there were probably fewer than a thousand individuals.
But the real measure of recovery depends not on how few but on how many whales there once were. That number is found nowhere in human records. It is found in the DNA of the whales themselves.
By analyzing mitochondrial DNA, scientists in a recent study have been able to use genetic diversity within the humpback population as a way to estimate pre-whaling numbers
. The current IWC estimate of the number of pre-whaling North Atlantic humpbacks, using a model based on whaling records and current sightings, is between 20,000 and 46,000. But the new genetic estimate — based on a far more accurate measure — suggests that the long-term population of North Atlantic humpbacks may have been about 112,000. This means that full recovery for humpbacks is much farther off than expected.
Kevin Schafer/Minden Images
A new genetic study indicates the pre-whaling population of humpbacks was far higher than previously estimated.
For a couple of decades now, scientists have been using mitochondrial DNA (and other genetic tools) to sort out questions of speciation and geographical origin. Who is kin to whom? Where did their ancestors come from? These are fascinating questions. But I’m struck by the question this new study asks: How many were there before we thought to count them?
Get that question lodged in your head, and you begin to realize that the history of our awareness of the biological world around us is a history of numerical indeterminacy. How many species are there? Estimates differ by the millions. How many bison were there on this continent before European contact? There is a wide range of estimates — nearly as wide as the range of estimates for the number of Native Americans living in those days. I somehow find myself wondering just how many dodos there once were.
We are the only species that goes about counting itself. As a result, knowing how many humpbacks there once were seems peculiarly important to us
— as a measure of an historical industry, as a guide to
The point of knowing the estimate of a long-ago population is what the numbers say about the world itself.
conservation management and, not incidentally, as an index of our environmental turpitude and righteousness. It matters too that the language we use to speak about whales has changed utterly. To be convinced of that, you need only dip into Moby Dick
, where the whale is more than leviathan: It is the dark beast within nature itself. Melville would not have understood the young Italian woman beside me out in a small boat watching humpbacks in Mozambique last summer. Whenever a fluke appeared or a whale breached, she would croon softly, almost maternally, “La balena! La balena!”
To me, the real point in knowing the mitochondrial estimate of a long-ago whale population is what these numbers say about the world itself. Could the North Atlantic now support a population of 112,000 humpback whales? And what’s the difference between a North Atlantic with 46,000 humpbacks in it — to accept the IWC’s highest estimate — and a North Atlantic with 112,000? After all, each humpback is a multiplier of sorts, an occupier of habitat, a utilizer of food resources, breeding opportunities, migratory routes, etc. To imagine a North Atlantic with the number of humpbacks that their DNA suggests must have existed is to imagine an ocean we would be unable to recognize. It would be a richer place than we can conceive.
I would like to know the mitochondrial numbers for the historical population of every species — how many there were before we thought to count them — just as I would like to have a far more accurate fix on the number of species on this planet. The reason is the most basic kind of biological accounting. A baseline is needed to understand the well-being of any species as well as the well-being of the robust yet infinitely delicate interlacing of life on this planet. Scientists have been working hard to establish such a baseline in our time so we can measure the adequacy of our conservation efforts.
But I’m interested in the baseline well before our time, centuries ago yet well within human history. Think of it as a way of discovering one of the real costs of being who we are — or, if you’re an optimist, who we happen
The real cost of the Anthropocene must be measured against the damage done to the web of all species.
to have been. If you go back 160 years to Matthew Maury’s “Whale Chart,” you get a momentary glimpse of the destruction humans brought to a handful of species within a handful of decades. You could construct a similar, if less accurate chart for other megafauna, like the gray wolf or the grizzly bear or the African elephant. But the real cost of the Anthropocene
— the era of our dominance — must be measured against the damage done to the collective web of all species, of which ours is only a single one.
Very soon, scientists will be able to extract even more accurate population data from mitochondrial DNA. Through relict populations, we will get a clearer and clearer glimpse of how richly this earth has been inhabited. I would like to believe that these numbers will help guide us toward ambitious new conservation goals. I hope too that they will carry the shock of revelation. Noah is supposed to have counted the animals two by two as they got on the ark. We face the risking of counting them two by two as they — and we — get off.
POSTED ON 11 Mar 2013 IN
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