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Ecoscenario: Monterey Bay National Marine Sanctuary 4/16/03 3:22 PM ISSUES A primary concern for the kelp forest is the impact of fishing, kelp harvesting, and ocean farming or mariculture. People have used the oceans as a source for food for centuries, fishing and hunting for fish, invertebrates, whales, and other sea animals. Historically, fishing and hunting have had a significant impact on the kelp forest ecosystem. Fishing European traders reported the vast riches of the West Coast oceans in the 1700s. Many countries sent explorers and traders to reap the wealth of the kelp forest. The Chinese began harvesting kelp, abalone, squid, and shark in 1850. Italian immigrants fished and supplied the markets in San Francisco. By 1900, abalone was so scarce that commercial harvest was banned. Offshore fleets of fishing ships came from Japan, Russia, and Vietnam. Monterey Bay is the location of Cannery Row, made famous in a book by John Steinbeck. The seemingly inexhaustible supply of sardines supported the local canning industry. In the 1940s and 1950s the sardine populations crashed, because of overharvesting and pollution. The sardine population has not fully recovered from this crash. While over 3 million tons of sardines were harvested file:///Ecoscenario/monterey/content.html Page 10 of 14
Ecoscenario: Monterey Bay National Marine Sanctuary 4/16/03 3:22 PM annually in the 1930s, only 5000 tons were caught each year in the 1970s. Regulations on sardine fishing have helped the population increase slowly since the mid-1980s. Limited fishing and hunting still occur in Monterey Bay National Marine Sanctuary. Several organisms, including kelp and abalone, are raised and harvested within the sanctuary. This method for farming the ocean is called mariculture. Sea otters Another concern was how the hunting of sea otters affected the kelp forest. Sea otters were hunted by Native Americans for thousands of years. In the mid-1700s Russia began hunting sea otters. Within 50 years the northern populations in Alaska were nearly eliminated. At about this time the Hudson Bay Company began hunting otters down the Pacific coast. By the 1920s only one colony existed south of Alaska, at Point Sur, California. The colony's location was kept secret by a small group of researchers. All the current California sea otters are descended from this colony. As the otters disappeared from some areas, the kelp forests also disappeared. Researchers wondered if the hunting of sea otters was related to the disappearance of kelp forests. Sea otters eat sea urchins, which in turn eat kelp. With their predator gone, sea urchin populations grew. Large numbers of urchins grazed on kelp stipes and holdfasts, clearing large areas of kelp forest. New kelp was quickly eaten by sea urchins. These kelp-free areas patrolled by sea urchins are known as urchin barrens. When sea otters returned to these areas, the kelp forest thrived again. This graph shows the number of sea otters in Monterey Bay National Marine Sanctuary from 1900 to 2000. Before sea otter hunting began in 1741, there were about 20,000 animals here. While the sea otter population along the California coast had grown to almost 2400 in 1995, in the last few years it has been declining. Sea otters are having just as many pups, but pups and adults aren't surviving as well. There are several possible causes for this decrease. About 40% of the dead sea otters found appear to have died from disease, which could be caused by increased pollution. Tissue from some dead otters had high levels of pesticides and agricultural chemicals like DDT. Oil from spills penetrates the fur, making it impossible for the underfur to stay dry. Oil and other pollution affects the populations of sea otter prey, which could impact sea otter survival as well. Accidents, such as being hit by a boat, are responsible for up to 20% of sea otter deaths. A few otters also die each year after becoming tangled in gill nets used by commercial fishers. Natural predators such as sharks also play a role. In Alaska, orca (killer whales) have recently been preying on sea otters. Researchers don't fully understand why the number of sea otters is continuing to drop. Giant kelp file:///Ecoscenario/monterey/content.html Page 11 of 14
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