On World Ocean Day, researchers have reported that jellyfish are taking over parts of the world’s oceans due to overfishing and other human activities.
Dr Anthony Richardson and his colleagues from the Australian CSIRO Marine and Atmospheric Research reported that their research has found that jellyfish numbers are increasing, particularly in South East Asia, the Black Sea, the Gulf of Mexico and the North Sea.
Jellyfish numbers are usually kept in check by fish, which eat small jellyfish and compete with them for food such as zooplankton. However, overfishing practices have allowed jellyfish populations to increase. This in turn has a significant impact on fish stocks, as jellyfish feed on fish eggs and larvae.
‘We need to take management action to avert the marine systems of the world flipping over to being jellyfish dominated,’ says Dr Richardson, who is also a marine biologist at the University of Queensland.
In Japan, fishermen are already having a real problem with giant jellyfish bursting through their fishing nets. This species, known as Nomura jellyfish, is the biggest in the world and can weigh up to 200 kilograms and can reach 2 meters in diameter.
The researchers have recommended a number of actions in a paper released today to coincide with World Oceans Day. They stress it is important to reduce overfishing, particularly of small pelagic fish, like sardines, to reduce run-off, and to control the transport of jellyfish around the world in ballast water and aquariums.