OSLO, March 26 (Xinhua) -- The stock of coastal cod fish in Oslo Fjord, southern Norway, decreased significantly and researchers have not found the cause, Aftenposten newspaper reported Monday.
"This is critical. Once of very high quantity, the cod is now almost completely gone. It is approaching Swedish conditions. They have barely had coastal cod for decades," biologist Sigurd Heiberg Espeland said.
An Institute of Marine Research expedition to look for freshly laid cod eggs found four or five eggs and some small crabs on Friday.
"Some years ago it was not unusual to have tens of eggs per catch," said Espeland, the leader of the expedition.
Many cohorts have vanished since the year 2000, and researchers do not yet know the real reason for this phenomenon, the report said.
"We know that recreational fishing is enormous in the Oslo Fjord. We know that climate change has made the water warmer. We know that there is a big construction activity and there is bursting and dredging in and around several harbors. Probably there are several unfortunate things that happened at the same time and those are the reasons for the collapse of cod numbers," Espeland said.
The situation is critical for the coastal cod population. There is an annual mortality rate of 75 percent. Up to 50 percent are fished by recreational fishermen, and 25 percent die of natural causes, according to the report.