Humans are a unique “super-predator” that hunts and kills other species many times more efficiently than the other top predators both on land and sea, scientists have found.
A study into the effectiveness of predatory animals has placed people head and shoulders above other top carnivores such as the lion and wolf on land and the shark and killer whale in the sea.
The researchers estimate that ocean fishing has resulted in humans exploiting adult fish populations at about 14 times the rate of other marine predators, while humans have hunted and killed adult land animals at around nine times the rate of other animal predators.
Human hunting and fishing has had an extraordinary impact on the natural world and its ruthless efficiency is laid bare in a detailed survey of 2,125 species of terrestrial and marine predators around the world, published in the journal Science.
The study revealed that human hunting and fishing is qualitatively different to the predatory behaviour shown by other species. It has, for instance, concentrated on killing mature adult animals rather than their offspring, which the scientists have likened to eating into the “reproductive capital” rather than the “reproductive interest” of the natural world.
Fishmongers inspect bluefin tunas before the first trading of the new year at Tokyo's Tsukiji fish market (AFP)
“Whereas predators primarily target the juveniles or ‘reproductive interest’ of populations, humans draw down on the ‘reproductive capital’ by exploiting adult prey,” said Tom Reimchen, professor of biology at the University of Victoria in British Columbia, Canada.
The study found that humans show another remarkable hunting trait by their ability to target other top predators as potential prey, especially in the sea where the decimation of top carnivores such as sharks, tuna fish and marlin has fundamentally changed the balance of some marine ecosystems.
“Our wickedly efficient killing technology, global economic systems and resource management that prioritise short-term benefits to humanity have given rise to the human super-predator,” said Chris Darimont, professor of geography at Victoria, and lead author of the study.
Yellowfin Tuna could be facing extinction after extensive human hunting (AFP)
“Our impacts are as extreme as our behaviour and the planet bears the burden of our predatory dominance….These are extreme outcomes that non-human predators seldom impose,” Professor Darimont said.
The scientists questioned whether current conservation policies, such as catching bigger fish and leaving the smaller, younger ones behind, have been the correct ones to pursue for sustainable fishing and hunting.
“In fact, the ‘sustainable exploitation’ paradigm in fisheries and wildlife management specifically calls for adult populations to be reduced by harvests,” Professor Darimont said.
“This paradigm, therefore, in fact instructs fishers and hunters to engage in this rather unnatural predatory behaviour, and explains why harvesters typically are required by law to release so-called ‘under-sized’ salmon, trout or crabs, or to set their rifle scopes on the 6-point elk and not the calves,” he said.
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By concentrating on bigger fish, for example, humans have altered the course of evolution for some marine species, making them mature earlier and so grow smaller. Yet older, bigger fish are often more fertile and so able to sustain a viable breeding population, the scientists suggested.
“Evolutionary change among humanity’s prey, wrought by targeting large adults, has shrunken body sizes, especially in fish. This is problematic because smaller fish have fewer offspring, and populations are no longer as resilient to harvests as before,” Professor Darimont said.
“The loss of large carnivores [on land], which has been in some or all part driven by over-exploitation, has caused diseases to emerge in herbivores valued by humans,” he said.
“Also, some herbivore populations kept in check by neither predators nor diseases have exploded, robbing food resources from a diversity of life, from insects important to humanity to birds we cherish,” he added.
