Overfishing, Damage to Coasts, and Ocean Health Indicators

Our oceans give us 90 million tonnes of fish each year! Unfortunately, we have often not fished carefully to conserve enough fish for the future. Canada recently closed its once-booming cod fishery. Why? Because people wrongly believed that oceans have a limitless supply of fish. In fact, since the 1970s, overfishing has decimated several of the world's biggest fisheries — anchovies in Peru, sardines in California, and herring in the North Atlantic.

• Around the world, more than 200 million people work in the fishing industry. More than five million people fish fulltime in Southeast Asia alone. When Canada shut down the cod fishery, 50,000 people lost their jobs. You can see how taking too many fish harms people and the economy.
• Overfishing harms many wildlife species. For instance, dolphins, birds, and Steller's sea lions have declined in the North Pacific. That's because we fished too much of their favourite food — Alaskan pollock. In the same way, Falkland Islands penguins starved to death when fishermen caught too many squid.
• Advanced technology allows fishermen to catch more fish. For instance, some huge trawling nets could trap 12 Boeing 747 planes.
• Fish face other threats, such as having their homes destroyed by pollution, dredging, logging, and development. That's why we need to look after watery ecosystems and not overfish. Countries around the world must also cooperate on who can fish how much and where. After all, our finny friends don't carry passports!

Coastlines form where the land touches the seas. Coastal areas provide homes for the oceans' biggest variety of wildlife. That's because they boast some amazing ecosystems — like reefs, mangrove swamps, and kelp forests — where watery creatures hang out. Humans like coasts too. Nearly 60 percent of all people live along them.

Many bird species migrate tremendous distances. They use coasts to fuel up for the long flight or as resting and eating spots along the way. Semipalmated sandpipers, for instance, stock up each August on the food-rich mud flats of the Bay of Fundy on Canada's East Coast. Then they fly three or four days nonstop to South America. Some other migrating creatures that count on healthy coastlines include seals, sea lions, and whales.

• The world's wildlife-rich coasts are the most abused part of our seas. Ninety percent of all ocean waste — about 20 billion tonnes of it each year — stays in coastal waters, where it poisons breeding grounds, disrupts sea-loving creatures, harms humans, and ruins beaches.
• Many of the planet's people live in horribly crowded settlements and depend totally on their fragile, polluted coasts for food and jobs. Small island countries could not survive without healthy coasts.
• We have already destroyed about half the world's coastal wetlands and many creatures living there. People have cut down half the world's mangrove forests to make artificial shrimp ponds.
• More than two-thirds of the world's largest cities sprawl along coasts. Singapore, for example, has destroyed nearly all its mangroves and coral reefs. Californians have filled in 60 percent of San Francisco Bay to make more land.

Now you know that all parts of our world depend on each other. When we harm one species or ecosystem, no matter how big or small, we eventually harm other species and spaces too. By protecting an ecosystem like the ocean, we also guarantee a healthy future for our planet.

Whenever a wildlife species begins to disappear, it could signal trouble ahead. Sometimes animal numbers dip temporarily for natural reasons, such as a very cold winter. But other times, disappearing creatures can mean we are polluting the air, water, or earth that the species needs to survive.

Scientists often rely on some wild creatures, known as "indicator species," to point out possible problems. Just about any species could indicate trouble if its numbers decline — or rise.

Here are some examples of indicator species:

• Mussels: They absorb many ocean pollutants, so scientists check out these shellfish for dues about the water's health. Mussels also point out nearby sewage. (Although most wildlife species become scarce around waste waters, colonies of the mussel Mytilus edulis actually grow around sewage.)
• Sperm whale: Biologists closely monitor the huge sperm whale. This species can sound an early warning because it lives in the open ocean, the area least affected by pollution. If this whale begins to vanish, biologists will know the oceans are in big trouble.
• North Atlantic right whale: Scientists keep a close eye on 300 of these endangered whales in the northwest Atlantic. The biggest threats to this species are ships, which can hit them, and fishing nets, which can entangle them.
• Beluga whale: Less than 100 years ago, more than 4,000 belugas swam in the St. Lawrence River. Today, there are only about 500. When they die, their bodies contain so many poisonous chemicals that scientists consider them toxic waste. The plight of these gentle whales forced the Canadian government to pass stricter laws on industrial river pollution.
• Osprey: This bird dives into freshwater or along ocean coasts worldwide to catch fish. As it is very sensitive to chemicals, such as pesticides, biologists watch the species closely for signs of decline.
• Plants: When aquatic plants grow out of control, it's usually a sign that nutrients (from fertilizers or sewage, for example) are polluting the water. Too many plants use up the oxygen supply shared by other living things, causing some species to suffocate. This process is called eutrophication.

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