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The precarious future of ocean megafauna

By Justin Gregg


Being an enormous, hulking beast has long been an effective defense mechanism. The plains and forests of North America were once teeming with colossal creatures like giant ground sloths and woolly mammoths, behemoths that plodded along safe in the knowledge that few predators would dare challenge them. But once prehistoric humans crossed the Beringia land bridge at the end of the Pleistocene, it was the largest animals that found themselves at the top of the kill list. Humans, armed with tools and complex hunting strategies, were well-equipped to take on these giants. And since one woolly mammoth carcass could feed a village for weeks, why bother wasting time with bite-sized squirrels or meager groundhogs? Being enormous, which was once these species’ greatest asset, was now their greatest liability. And so, 10,000 years ago, our ancestors hunted the great North American megafauna to extinction.

We face a similar situation today. But this time, we’ve turned our attention to the ocean megafauna. Our great-grandfathers began targeting the largest whales first, hunting most species to near extinction. When 18th century European traders first happened across the nine meter long Steller’s sea cow along the coastlines of the Pacific North West, they finished what the aboriginal hunters had begun, slaughtering the very last of these gentle giants just 27 years after first setting eyes on them. But it’s not just aquatic mammals that we pursue without mercy. Our modern fishing methods have allowed us to pull giant tuna species out of the ocean by their millions. A global taste for sushi has reduced bluefin tuna numbers in the Northern Pacific by 96%. Their rarity means that a single bluefin tuna can now sell for over $1.5 million.

Atlantic bluefin tuna (Thunnus thynnus) ensnared near the mouth of the fish trap. Public Domain.

Atlantic bluefin tuna (Thunnus thynnus) ensnared near the mouth of the fish trap. Public Domain, courtesy of United Nations Food and Agriculture Organization.

It seems that any sea creature that has the unfortunate trait of growing larger than the size of a coffee table is destined to run afoul of humanity. Manatees, sharks, manta rays, sailfish, sea turtles — the bigger the beast, the bigger our desire to kill it, eat it, stuff it, and mount it. And even when not hunting them on purpose, ocean megafauna are, due to their size, at serious risk of being pummeled by boat and shipping traffic or inadvertently drowned in fishing nets.

The IUCN Red List shows the extent of our thirst to exploit ocean megafauna. One third of pelagic sharks species are threatened with extinction — due almost exclusively to overfishing. This includes some of the largest of all shark species, including basking sharks, great white sharks, and great hammer head sharks. “Despite mounting threats, sharks remain virtually unprotected on the high seas,” says Sonja Fordham, Deputy Chair of the IUCN Shark Specialist Group. The demand for shark products, including shark fins for use in soup, has increased shark slaughters by 400% in the last 50 years. With shark fins selling for up to $256 per pound, and a single whale shark fin fetching up to $15,000, it is the largest shark species that bear the brunt of our insatiable appetite.

Ocean dwelling reptiles aren’t safe either. Of the seven marine turtle species alive today, five are listed by the IUCN as either “endangered” or “critically endangered.” The largest species, the leatherback turtle, can reach 1.8 meters in length and weigh over 500kg. But its bulk makes it vulnerable to entanglement in fishing nets, and its eggs are still collected and eaten in some areas of the world. Fishing nets pose a serious threat to many of the larger marine mammal species, with 70% of critically endangered North Atlantic right whales having been entangled in nets at least once in their lifetime. Entanglements and ship collisions are making it impossible for this species — numbering approximately 400 individuals — to claw their way back from the brink of extinction. Their enormous size, which once protected them from predators, will ultimately be their downfall.

It is entirely possible to cease the exploitation of ocean megafauna. There are campaigns to stop shark finning, protect endangered dolphin and whale populations, cease over-fishing, etc. It is not too late to reverse the current trends. So on this World Animal Day, why not pick a cause and a species that most excites you and get involved in the fight to preserve these ocean giants. Let’s not let animals like tuna, right whales, and great white sharks slip quietly into the history books alongside the sea cows and mammoths.

Justin Gregg is the author of Are Dolphins Really Smart? The Mammal Behind the Myth. He is a research associate with the Dolphin Communication Project, and Co-Editor of the academic journal Aquatic Mammals. He received his doctorate from Trinity College Dublin in 2008, having studied social cognition and the echolocation behavior of wild Indo-Pacific bottlenose dolphins. With an undergraduate background in linguistics, Justin is particularly interested in the study of dolphin communication as it pertains to comparisons of human (natural) language and animal communication systems.

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