Fingers are pointing at the Chilean aquaculture industry as the worst red tide in that country’s history has caused massive die offs of bi-valves and vertebrates. Earlier this year an estimated 40 000 farmed salmon were killed when the micro-organisms that produce the toxin poisoned them.
The dead salmon were disposed of at sea, much to the chagrin of local fishermen.
The single celled plankton can reproduce rapidly when warm water and sufficient nutrients become available. They can reproduce rapidly and in sufficient numbers to colour the water a reddish hue. The toxin that they produce does not normally poison shellfish but because shellfish are filter feeders, they accumulate enough of the poison to kill animals with backbones.
his month an estimated 8 000 tons of dead sardines washed ashore. This die off has also included millions of the shellfish as well. Their shells are also washing ashore. Estimates of a 70% kill off the bivalves have been made. Thousands of dead cuttlefish have washed ashore.
Shellfish paralytic poisoning can kill humans that eat contaminated seafood.
The cause of the red-tide may not be the tons of farmed salmon dumped off shore. Some scientists attribute the massive kill off to the warmer ocean temperatures caused by the El Nino phenomenon. It is likely to be a combination of factors which include water temperature and available nutrients like rotting fish.
Red tides have been increasing in frequency in cooler waters as well. Off the coast of Vancouver Island, it used to be safe to harvest wild oysters in months that contained an “R” in their name. That is no longer the case as agricultural runoff and sewage disposal into coastal waters have provided ‘nutrients’.
Those people who have been able to make a good living fishing and collecting shellfish have been thrown out of business. The Chilean government has offered them the equivalent of USD 150 per month to survive. The enraged fisher folk marched on government offices.
Chile’s coastal waters have been hit with a series of big die offs recently. Last year over 300 dead whales washed ashore.
The El Nino phenomenon has been particularly strong this year. The waters of the Pacific Ocean have warmed more than usual. This has led to numerous weather disruptions around the globe.
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