Algae biotoxin studied in July whale deaths
by Doug Fraser - staff writer
Cape Cod Times
23rd October 2003
Researchers looking into the deaths of 21 large whales, mostly humpbacks, have found traces of a naturally occurring, but deadly, biotoxin produced by algae in tissue samples taken from five of the whales.
"It's not exactly a smoking gun, but it's the most significant finding to date," said Katie Touhey of the Cape Cod Stranding Network, in a press release.
Touhey is coordinating the investigation into the deaths, which were all observed between July 3 and July 30. The findings were released Tuesday in Newport, R.I., at the annual meeting of the Marine Mammal Commission, which advises federal agencies on how to best meet the goals of the Marine Mammal Protection Act.
National Oceanic and Atmospheric Administration Fisheries spokesperson Teri Frady said yesterday that the investigation was launched after her agency declared the whale deaths an "unusual mortality event.” That designation applies when the deaths involve groups of animals within the same species, found in the same area around the same time. The whale carcasses were all sighted on eastern Georges Bank and off Southern New England.
The biotoxin found in the animals is domoic acid and is produced by an algae species called Pseudo-nitzschia. This algae is present in the ocean as one type of phytoplankton that blooms when water temperatures and sunlight are just right.
Under certain conditions they reproduce rapidly in dense concentrations known as plankton "blooms.” When fish or shellfish feed on blooms that contain toxic species, they tend to ingest enough poison in their tissues that they are poisonous to mammals.
One such poisonous bloom is commonly known as red tide. Algae in those blooms produce saxitoxins that cause potentially lethal shellfish poisoning, and cause shellfish beds to be closed until toxin levels drop to safe levels. The Nauset estuary system has a persistent outbreak of red tide each year that closes it down to shellfishing for most of the spring and early summer.
Domoic acid causes a condition known as amnesic shellfish poisoning (ASP). It would be most familiar to movie buffs as a result of a well-publicized attack on the California seaside town of Capitola by hundreds of seabirds, which were suffering from poisoning after eating tainted fish. The birds' attacks on people, street lamps and windows inspired the 1963 Alfred Hitchcock movie "The Birds.” Symptoms in humans include vomiting, diarrhoea, short-term memory loss, cardiac arrhythmia and, possibly, death.
Domoic acid and ASP have been a plague to Washington state shellfishermen and have been responsible for whale and other mammal deaths on the West Coast.
If domoic acid turns out to be the cause of the East Coast whale deaths it will be the first known deaths from ASP in the region.
Frady said whale samples have thus far tested negative for the more common saxitoxins.
The first reported human outbreak of ASP on the Atlantic Coast was in 1987 on Canada's Prince Edward Island, when three people died and more than 100 were poisoned after eating tainted mussels. While the Massachusetts Division of Marine Fisheries does test for paralytic shellfish poisoning toxins in shellfish, it does not test for ASP, a department spokesman said yesterday.
A second investigation
Federal investigators are also looking into the deaths of seven minke whales and 40 to 42 harbor seals that took place off the coast of Southern Maine from Aug. 10 to Oct. 2. Frady said the harbor seal deaths were double the usual rate for such a time period, and consisted almost entirely of adults. Dead seals at that time of year are usually juveniles who have not thrived in the competition for food or have died from natural causes.
"We do have samples from many of the whales and from six harbor seals," Frady said.
Researchers are also examining photographs of dead animals taken at sea. When those deaths were first reported, there was some controversy over marks on some of the whales that indicated they may have been hurt by fishing gear.
Some fishermen blamed pair trawlers, which tow large nets between two boats to catch herring, a favourite food of whales and seals. Frady said there were some marks on the whales and seals that might be from fishing gear, or could be due to decomposition.
The Maine marine patrol and NOAA law enforcement are both investigating the whale and seal deaths.
"Nothing has been ruled out," Frady said.