Mediterranean wild fish are exposed to exotic viruses because of huge quantities of imported feed-fish used in tuna farming, says a report by the World Wildlife Fund (WWF). The global conservation organization is asking the EU to urgently ban the use of non-Mediterranean fish as feed in tuna farming.
The report claims that during their captivity, which lasts about six months, tunas are fed on large quantities of feed-fish. Most of it consists of imported frozen, untreated fish from other regions (West Africa, the North Atlantic, and North and South America) and involves non-Mediterranean species such as herring or capelin.
As a result, as much as 225,000 tonnes of feed-fish – most of them alien to the region – are used annually by tuna farms in the Mediterranean, a higher number than the area’s annual catch of sardines. This could lead to the introduction of new viruses that might affect the whole Mediterranean ecosystem.
“Dumping of imported feed-fish into the Mediterranean tuna farms must stop immediately. It threatens both the health of local fish populations and ecosystems and the livelihoods of fishermen that rely on them,” said Dr Sergi Tudela, Fisheries Coordinator with WWF's Mediterranean Programme Office.
With Spain, Malta, Italy, Greece, and Cyprus accounting for 71 per cent of the officially declared tuna farming activity in the Mediterranean, the problem is mainly European and the EU has the responsibility to halt the threats.
The WWF report highlights the case of alien feed-fish imports dumped by tuna farms in Australia in the 1990s. Massive imports of small fish from other regions were at the origin of viral epidemics that in 1995 affected 5,000km of coastline and killed 75 per cent of the adult sardine population in Australia.
“The risk of disease transmission is very high. Most fish viruses rely either on direct feeding or proximity to spread, and we set up a classic transmission experiment every time we feed sardines to tuna,” said Dr Brian Jones, fish pathologist with Western Australia’s Department of Fisheries and expert on the Australian case.
“It is technically impossible to analyze regularly frozen feed-fish imports to ensure that they are free from harmful viruses. The only solution is to have a total ban of such practices. In Denmark, use of feed fish in saltwater aquaculture has been banned since 1985. The EU should take the same approach to Mediterranean tuna farms,” added Dr Tudela.