Minneapolis Star Tribune

Distributed by Tribune Content Agency

Evidence mounts that our waters are deteriorating because of chemical runoff, acid rain, climate change and invasive species — and now this: We may be catching the wrong-sized fish.

An article published this week in the journal Science contrasts the behavior of predators in the wild with that of humans. For the most part, natural predators select younger, smaller, weaker individuals for food, while humans go after mature, trophy-sized fish and other large animals, not just for food but for sport. Nature’s selection scheme tends to produce balance between the eaters and the eaten, while human practices tend to deplete wildlife populations. Why? Because humans kill animals in their reproductive prime.

Canadian researcher Chris Darimont, a conservation geographer at the University of Victoria, spent 10 years studying 400 species in the world’s oceans and on six continents and found that humans killed adult animals at a rate up to 14 times higher than did nonhuman predators. The greatest difference came in how humans fish.

We are told to throw back the small fry and keep the adults, but a female cod that lives long enough is a “cod-making machine,” Darimont told the Associated Press. Human practices of hunting and fishing have changed the rules of nature’s game, he said, from survival of the fittest to survival of the smallest.

Compounding the imbalance is the human preference to hunt and fish for other carnivores — including lions, tigers and other large game — while nonhuman hunters kill proportionally more plant-eating species. Indeed, what most characterizes human predators is the stunning breadth of their appetite. No other animal preys upon thousands of other species, Darimont said.

All of this adds up to “striking differences” between animal predators and contemporary humans, Darimont concludes, citing enormous advantages that humans have amassed over the centuries, including killer technologies, rapid population growth and the domestication of dogs.

The upshot is that humans have evolved into “super predators” unwilling or unable to maintain the natural equilibrium. All manner of “normal” human activity — including global trade, fossil-fuel subsidies, food processing, and recreational hunting and fishing — contribute to failing ecosystems worldwide.

The Darimont research is both troubling and welcome. It adds to the growing awareness that all sorts of “normal” human behaviors are tilting nature in a dangerous direction. Scientists said last week that global warming caused by human emissions has exacerbated the severity of the current California drought by 20 percent. Scientists in Minnesota have said repeatedly that agricultural practices and suburban-style development are helping to destroy the state’s cherished lakes. We’ve met the enemy, and the enemy is us.