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article imageWhat is killing the giant ‘Ocean Sunfish’ off the coast of Chile?

By Igor I. Solar     May 17, 2013 in Environment
Iquique - Several specimens of Ocean Sunfish have washed ashore along the coast of Chile in recent months. The gigantic fishes, always in solitary, cast aground on sandy beaches and the cause of their death remains a mystery to researchers.
The latest sunfish stranding occurred two days ago (Wednesday May 15) on the beach “El Colorado” of the northern Chilean port of Iquique. The huge marine animal was found on a sector of the beach hit by large waves. Members of conservation organizations, Kaitieki and Sea Shepherd, attended to the site to attempt a rescue or to collect data, according to local media.
The sunfish measured almost 2 meters long by 1.5 meter high and weighed about 800 kilograms. It had no visible wounds or lacerations, and based on the condition of fish, it washed to the shore after dying offshore within the previous two days.
Ocean Sunfish stranded on  El Colorado  Beach  Iquique  Chile.
Ocean Sunfish stranded on "El Colorado" Beach, Iquique, Chile.
The death of a fish of this species has become a recurrent event on beaches along the Chilean coast. On 24 April, a fish of this species was found dead on the same beach. In January this year, another specimen was found dead near Castro in Chiloé Island, located in the south of Chile. On March 15, another fish of this species was found dead on rockeries of islet “El Alacrán” of Arica, Chile’s northernmost port. And on March 2012, a sunfish stranded on a beach in Dalcahue, also in the Island of Chiloé.
Despite detailed inspections by specialists, the causes of death of these fish are not apparent and remain a mystery. Because of their size, in the range of 300-800 kilos, these fish would be still relatively young.
The ocean sunfish (Mola mola, also known as "Moonfish") is the world’s largest bony fish with an average weight of 1000 kg. Some specimens may reach over 3 meters in length and can weigh up to 2 tons. The species is cosmopolitan, inhabiting tropical and temperate waters around the globe. Its body is flattened laterally. Its general appearance is that of a big head with a tail, lacking a caudal peduncle. The pectoral fins are very small, but they have large dorsal and anal fins. Other marine fish, such as some sharks, are larger than the Ocean Sunfish, but these are fish with a cartilaginous skeleton.
Giant Ocean Sunfish in Bali  Indonesia.
Giant Ocean Sunfish in Bali, Indonesia.
Kevin Deacon.
Little is known about the biology of this fish. However it is known that, because of its size, it has few predators. These include killer whales, sharks and sea lions, which mostly attack juvenile sunfish. According to observations of animals in captivity, sunfish are known to live up to 10 years and they grow fairly fast. A specimen in the Monterey Bay Aquarium, California, grew from 26 kilos to almost 400 kilos in 13 months.
In the Eastern Pacific they can be found in tropical and temperate waters from British Columbia, Canada, to Perú and Chile. However, their presence in the Chilean coast, bathed by the cold Humboldt Current coming from the Antarctic, is rather infrequent. Apparently, because of probable variations in the oceanography of the eastern Pacific Ocean, these fish may have lost their way and entered waters with conditions hardly favorable to their survival.
The surveillance of new occurrences of these giant fish on the beaches of Chile continues. The hope is that they will stop appearing dead on the beaches, but remain living and reproducing in their usual environment, the world's temperate and tropical oceans.
More about Ocean sunfish, Mola mola, Chilean beaches, fish strandings, marine biology
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