Drivers of Biodiversity Loss: Overexploitation

Over the past 50 years, the natural world has experienced unprecedented rates of change with devastating implications. Today, approximately one million species are at risk of extinction globally, and integrally linked ecosystem services—from disease buffering to pollination—are at risk of loss. The direct drivers of biodiversity loss with the largest global impact are: changes in land and sea use; exploitation of organisms; climate change; pollution; and invasion of alien species. These drivers are primarily a result of underlying societal values and behaviors. If left unaddressed, they are predicted to continue or increase their detrimental impact. Transformative action is needed to alleviate these threats.

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People have a long history of overhunting and exploiting species, driving them to extinction. Early humans are believed to have hunted several species of large mammals to oblivion, such as the giant ground sloth, mammoths and saber-toothed cats. However, there are several famous extinctions during more recent times, such as the dodo and Steller’s sea cow, both of which were found in small populations on remote islands but were hunted out in the 17th and 18th centuries, respectively.

One of the most spectacular examples of overexploitation in U.S. history is the passenger pigeon. The passenger pigeon was not some remnant population on a remote island but rather the most abundant bird in North America, with a pre-exploitation population size estimated in the billions. The bird traveled in vast flocks, so dense that they made the sky dark. But large-scale hunting for meat, feathers and crop protection led to the species becoming extinct in the wild by the end of the 19th century, with the last passenger pigeon dying in 1914 at Cincinnati Zoo.

Another once-abundant species that was nearly hunted to extinction is the sea otter. Once numbering in the hundreds of thousands, sea otters extended from Baja California, up the U.S. west coast and around the shores of the northern Pacific to Russia and Japan. In the early 18th century, Russian hunters started killing sea otters in the Kuril Islands, selling their fur to Chinese traders. It didn’t take long for a major sea otter hunting industry to take off.

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Ingrid Valda Taylar

The sea otter has the densest fur of any mammal, an adaptation to their cold marine water habitat. Unfortunately, this dense, warm fur also became highly sought-after, so much so that it became referred to as “soft gold.” So began the “great hunt” in which over a million sea otters were killed, depleting the world population to just a couple of thousand animals worldwide.

By the mid-19th century, sea otters had been severely depleted throughout much of their range. Only 13 small populations remained, each numbering just an estimated 10–100 animals. Their near extinction led to the first international wildlife protection treaty—the North Pacific Fur Seal Convention of 1911, which introduced international protections to both depleted sea otters and northern fur seals. 

It was thought that the sea otter in California had been hunted to extinction, like in neighboring Mexico and along the Washington and Oregon coasts. However, in the 1930s, a single colony of about 50 animals was discovered. In 1977, the California, or southern, sea otter was listed under the U.S. Endangered Species Act.

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Morgan Rector

After the cessation of commercial hunting, sea otter populations in Alaska began to recover; however, otters have declined dramatically in southwestern Alaska over the past two decades and sea otters there remain susceptible to a host of other natural and human-caused perturbations. The current California population of roughly 3,000 animals grew from the single colony noted above, but they have not expanded into much of their historical habitat.

Even after more than a century of protection, sea otters still face many threats. Although the commercial overhunting that decimated sea otters historically has ceased, a small amount of illegal poaching still occurs. In addition, entanglement in fishing gear, predation, disease, deliberate shooting, boat strikes, oil spills and climate change also threaten sea otters. 

In California, sea otters have suffered from outbreaks of toxoplasmosis, a disease caused by the protozoal parasite Toxoplasma gondii, which is only transmitted by cats when the infective stage of the organism in their poop washes into the ocean. The Exxon Valdez oil spill in Prince William Sound, Alaska, impacted over 1,300 miles of coastline, killing at least 3,000 otters and affecting the health of many more. Although improvements have been made to the safety of oil tankers, oil spills still occur in sea otter habitat. Finally, climate change presents another risk to sea otters, with rising sea levels, more severe storms and changes in ocean ecosystems threatening otter populations.

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Joshua Asel

Overexploitation brought the sea otter to the brink of extinction, and even today southern sea otters only occupy 13% of their historical range. Without question, the loss of this top predator from kelp forests and estuaries caused an extensive decline in the biodiversity of nearshore ecosystems around the Pacific Rim. Now, conservation organizations like Defenders of Wildlife, academics and government agencies are working to restore sea otters along more of their coastal range. Recent research has shown that the economic benefits of such sea otter restoration—increases in finfish biomass and primary productivity, expansion of kelp and seagrass systems that sequester atmospheric carbon, and wildlife tourism—are seven times more valuable than the anticipated economic losses that sea otters might cause to fisheries.

In 2006, Defenders of Wildlife worked with California lawmakers on legislation that established the California Sea Otter Voluntary Tax Contribution Fund, a voluntary contribution option on the state's tax forms. The fund pays for scientific research, public education and law enforcement that benefits sea otters. Hopefully, we can work to bring back this keystone species to the rest of its original habitat and restore biodiversity along Pacific coastlines.

Establishing a National Biodiversity Strategy

The U.S. lacks a comprehensive and coordinated approach to tackling the five main drivers of the biodiversity crisis. Worldwide, 194 other countries have developed forms of a national biodiversity strategy. A national biodiversity strategy would address the extinction crisis by requiring more effective and coordinated use of laws and policies to protect biodiversity and reverse its decline, while reasserting the U.S.’ international leadership.

It’s time for America to lead—to demonstrate how we can live in harmony with nature and to respect our environment. We cannot think of a more important roadmap toward a sustainable future than a comprehensive national biodiversity strategy. It will help us prioritize and safeguard the natural resources that are critical to humanity’s survival.

The time to invest in our planet is now, before it’s too late.