Jellyfish Boom Linked To Overfishing
May 4, 2013

Overfishing To Blame For Jellyfish Population Boom

April Flowers for - Your Universe Online

Jellyfish, in all their many varieties, have invaded many of the world´s seas, including the Sea of Japan, the Black Sea, and the Mediterranean Sea since the beginning of the 2000s. Researchers question this phenomenon, trying to understand the underlying causes. Is it cyclical? Is it caused by changes in marine currents, or global warming?  The causes of the jellyfish boom have remained a mystery until now. A new study, led by the Institut de Recherche pour le Developpement (IRD) in France, reveals the underlying mechanism to be overfishing.

Tuna, sea turtles and other jellyfish predators are disappearing due to overfishing. While that helps the jellyfish, they are truly taking advantage of the overfishing of small pelagic, or open ocean, fish. Fish such as sardines, herring, anchovies and others feed off of zooplankton, making them the main competition for food. Small fish such as these also eat the jellyfish eggs and larvae, acting as a regulating force on the population. In areas where these fish are depleted due to overfishing, an ecological niche is opened up for the jellyfish, and they are filling it at an alarming rate.

The research team compared two ecosystems belonging to the same ocean current, the Benguela, which flows along the south of Africa, in order to demonstrate the role of overfishing in the jellyfish proliferation. Off the cost of Namibia, fish stock management measures are not very restrictive. The fish populations are barely allowed to replenish before fishing begins again. Jellyfish are currently colonizing this ecosystem. The opposite is true in the second ecosystem, 1,000 miles south off the coast of South Africa. Fishing in this area has been tightly controlled for the past 60 years, and the jellyfish population has not increased.

The affected areas are seeing the development of a vicious cycle. Marine food chains are more flexible than those on land, as the prey species can feed off their predators. Jellyfish do just that by eating larval fish. Combined with overfishing, this prevents the renewal of fishery resources and threatens the economic survival of the industry. In Namibia alone, some 10 million tons of sardines in the 1960s have made way for 12 million tons of jellyfish.

Jellyfish affect the economic health of a region in other ways as well. They are the pet peeve of tourists, for example. A jellyfish´s sting is rarely fatal, but it is extremely painful, with itching and swelling to add to the discomfort. The risk of being stung keeps many tourists away, placing the economic health of the region at risk as well. This is particularly harmful in developing countries which depend on tourist income.

The researchers say their findings, published in the Bulletin of Marine Science, highlight the need for an ecosystemic approach toward the exploitation of the sea, taking into consideration all levels of the food chain,