In 2009 the Diasan Shinsho-maru, a ten-ton trawler was fishing in Tokyo Bay.
When the fishermen hauled in their nets, the nets were full of giant jellyfish.
When the weight of the jellyfish broke the net, the thousands of pounds of jellyfish
cascaded onto the ship’s deck and capsized the boat.
The 3 fishermen aboard were thrown into the sea but were fortunately rescued by another
trawler.
The jellyfish were Nomura jellyfish and lots of them.
These jellyfish are only one species of gelatinous creatures that have roamed Earth’s oceans
for the last 500 million years.
In the twentieth century, the gigantic Nomura Jellyfish would mysteriously appear in the
East Asian seas about once every forty years.
Starting at the turn of this century however, large groups of jellyfish called “blooms”
began making more frequent visits and recently, since 2005 they have appeared every year.
The Nomura Jellyfish is one of the largest jellyfish known to exist.
What is odd about these jellyfish is that in recent years they have grown to gigantic
sizes.
The crown or head of the Nomura jellyfish now inundating the Japanese coastline measures
7 feet across and they weigh 450 pounds, heavier than a sumo wrestler and their tentacles can
measure 100 feet or more in length.
There are many different jellyfish species in the world – at least 350, and possibly
over 2000.
Jellyfish range in size from about a millimeter to 2 meters in diameter.
Their stings are extremely painful and in some cases have caused death.
Death from a Nomura jellyfish however is rare.
Jellyfish are free swimming gelatinous animals and are a normal element of marine ecosystems.
Fish and jellyfish however compete for plankton.
The Nomura jellyfish normally lives between China and Japan, migrating from the Yangtze
River to the Yellow Sea.
They float across the Sea of Japan on the Tsushima Current.
In summer when the water is warmer, they move to the coasts of Japan and Korea.
Even with their huge size, a few of these animals isn’t much of a concern.
However, their populations have been exploding since 2002, and they are now wreaking havoc
on the Japanese fishing industry.
Giant jellyfish are overpopulating the world’s oceans, especially around Japan.
They weigh down and damage fishing nets, and their toxins sting fish and make the fish
inedible.
In a country where fish is one of the economy’s mainstays, the results have been disastrous.
Fishermen in some areas of the country stopped going out altogether and many cited an 80
percent drop in their income.
Nobody is one-hundred percent sure what is causing the invasion.
Some scientists believe that it is because the water temperatures in the area have increased
by 1.89 degrees Fahrenheit, which is better for jellyfish to breed.
Overfishing is likely another factor.
Fewer numbers of fish means less competition for the jellyfish and fishing nets is killing
off large numbers of sea turtles, a natural predator of jellyfish.
Throughout the world we are seeing rising numbers of jellyfish and they are often found
in areas heavily impacted by humans through pollution, overfishing, and warming waters.
Losses from marauding mobs of giant jellyfish in the Sea of Japan typically total hundreds
of millions of dollars during a single bloom season.
No one knows for sure why blooms of giant jellyfish in Asian waters are becoming more
common or where the Nomura’s jellyfish originate but Dr. Shi-ichi Uye from Hiroshima University
in Higashi-Hiroshima, Japan has identified a possible scenario.
The availability of zooplankton is just everywhere.
They use that strategy rather than attacking a larger prey.
In the previous century the bloom happened once every 40 years cycle.
That means that one time in 40 years.
However, from the turn of the century, it’s become an annual event.
That means it occurs almost every year.
For the past 4 summers, these massive sea creatures have mysteriously materialized in
the Yellow Sea off China and the Korean peninsula before drifting across into the Sea of Japan.
One theory suggests that Chinese coastal waters are currently being degraded.
This degradation is associated with environmental pressures generated by the 800 million people
who currently live along the coasts of the East Asian Marginal Seas (EAMS), which include
the Bohai, Yellow, East China and Japan Seas.
Many of these environmental pressures on the EAMS promote the proliferation of giant jellyfish.
Dr. Uye has conducted laboratory studies of the larva of giant jellyfish, which live as
tiny polyps that can reproduce asexually before developing into free-swimming jellyfish.
They’re distributed quite widely in East Asian waters not only in the Chinese and Korean
waters but also Japanese waters.
They come to the city side of the Japanese coast.
So their distribution is really wide.
Dr. Uye has documented the movement of young giant jellyfish from Chinese waters into the
Sea of Japan on currents, and their astounding growth along the way.
He suggests that the rising water temperatures may increase the rate of polyp reproduction,
and speed their development into free-swimming jellyfish.
Populations of predators and competitors of jellyfish, which usually help control the
jellyfish populations, are being eliminated by overfishing.
The flow of runoff containing fertilizers and sewage into Chinese coastal waters promotes
the growth of tiny plankton which provide food for the giant jellyfish.
The Three Gorges Dam on the Yangtze River may be changing the chemistry of China’s
coastal waters in ways that support jellyfish blooms.
It is thought that the amount of phosphorous and nitrogen in these waters make an ideal
breeding ground for the Nomura Jellyfish.
These waters have probably also been further enriched in nutrients due to the increased
farming activity.
The development of Chinese ports and harbors has provided the Nomura larvae with new places
to attach themselves.
The area near the confluence of the polluted Yangtze River with the East China Sea is believed
to provide a breeding ground for giant jellyfish.
Jellyfish are, however, notoriously difficult to study, so there isn’t much research available.
The Nomura jellyfish have become such a problem in Japan that an official committee has been
formed to combat them.
Some scientists believe that these sea animals could serve as a key indicator for the health
of the oceans, so scientists are now building a database of jellyfish.
Scientists are aware that they must take care when gathering specimens for research since
a 450 pound jellyfish can capsize their small research boats when retrieving the specimen.
It is very difficult to get rid of these giants because whenever they feel under attack or
threatened, Nomura Jellyfish release billions of sperm or eggs which attach to corals or
rocks, detach and grow into more jellyfish, millions at a time.
It is estimated that the current bloom of these giant Nomura jellyfish located in and
around the entire coasts of Japan and the Sea of Japan number in excess of 500 billion.
Despite numerous attempts, the problem of these giant Nomura jellyfish keeps getting
bigger and some viable method will have to be found quickly to deal with them.