A fishing ban sparked by mass deaths of sea creatures in Chile has left tourists stranded and markets empty on an island cut off by protest blockades.

In the south of the world's second-biggest salmon-producing country, fishermen have blocked roads with burning tires. They have cut off access to the island of Chiloe in the picturesque Los Lagos region.

They are furious at what they say is paltry compensation offered to them by the authorities for the so-called "red tide" that is ruining their livelihoods.

Heaps of dead salmon, sardines and clams have washed up on the nearby Pacific shores over recent months, choked to death by a surge in red algae.

Some scientists say the algae are thought to have proliferated due to the El Nino phenomenon, which warms the Pacific to wreak havoc with the weather in Latin America every few years.

Fishermen accuse the salmon farming industry of worsening the effect of the algae by tipping contaminated salmon into the sea -- a claim the companies deny.

The government initially offered fishermen's families vouchers worth $150 each to tide them over, but they angrily rejected that.

The government has since upped its offer to total about $1,000. Economy Minister Luis Felipe Cespedes asked the fishermen's groups to "be reasonable."

But with their livelihoods threatened by an environmental crisis that could last months, they are demanding more in ongoing negotiations with Cespedes.

- Schools, roads, markets closed -

Schools stayed closed on Monday in various districts of the island, home to 170,000 people.

Chiloe's petrol stations have run dry and are closed. To buy fuel, locals have to get a ferry to the mainland, but permits to do so -- issued by the protest leaders -- are scarce.

Many tourists are stranded.

"We arrived on April 25 and then this chaos broke out," said Nora Vivente, an Argentine visitor to Chiloe.

"Their demands are just and we support them, but regrettably it affects us. We would like them to find a solution so that we can continue on our way."

Cespedes said Friday he had ordered a group of independent scientists to investigate the fishermen's claim that the salmon farming industry was to blame.

Chile is the second-biggest producer of farmed salmon in the world after Norway, according to the industry organization Salmon Chile.

Although southern Chile sees red tides every year, this year's extended farther north than usual, said Jorge Navarro of the marine institute IDEAL.

"It affected bivalve populations (such as clams) that had never before been exposed like this" to the algae, he said.

The southern Chile labor unions' federation estimates the red tide has killed 30 million salmon.

It says sales of fish and seafood from the region have dropped 90 percent and 10,000 employees in the salmon industry are out of work.

"We are facing the worst social and economic conflict of our time... which affects the direct livelihood of thousands of families," it said in a statement.

In the island's second-biggest town Ancud, the tourist market was closed for lack of business.

"It is affecting us badly," said one vendor, Maria Altamirano. "Sales are right down. There is nothing to buy and nothing to sell."