The deaths of so many sea creatures in Nova Scotia has led everyone, from researchers to armchair scientists, to offer theories as to the cause of the die-offs. And it appears that, right now, no theory is too far off-the-wall to warrant consideration.
The Canadian Department of Fisheries and Oceans (DFO) has been keeping the public updated via their Twitter account, and today, the DFO gave a live update at a news conference.
According to CBC News Canada, federal scientists said that so far, nothing out of the ordinary had been found in environmental testing. Scientists were out on the water Thursday, collecting water samples, testing dissolved oxygen, salinity, and temperature – all of the parameters being normal.
The DFO also showed a video taken at the bottom of St. Mary’s Bay, off the Bay of Fundy. The video appeared to show normal conditions with no dead fish or other marine organisms one would expect in a mass die-off. “We have ruled out the usual suspects,” said Kent Smedbol, manager of population ecology for DFO.
But needless to say, testing for pesticides, amnesic shellfish toxins, paralytic shellfish toxins, & diarrhetic shellfish toxins, anemia, and viral diseases, have all turned up negative, adding to the mystery.
Four possible theories on the cause of the marine die-offs
On Thursday, reports CTV News Canada, Smedbol talked about some of the causes scientists are looking at in relation to the marine animal deaths.
Some kind of disease is always a suspect in animal die-offs, but diseases, both bacterial and viral have been ruled out in this case. As for viral testing, a preliminary molecular test for viruses was used, and while the tests came back negative, culture-based viral studies will take some time before they are completed.
Storm runoff is also a possible suspect. We know that runoff from storms can affect the salinity of seawater close to shore, dropping the salinity temporarily. Runoff from agricultural sources can also be a problem. This is what happened in Florida in March this year.
In the Florida fish-kill, a trio of environmental factors played a role, including warmer waters, increased precipitation, and pollutant runoff, according to CNN News. The combination of factors resulted in toxic algae blooms and a brown tide that depleted the oxygen in the water.
Human-made pollution is also being considered, said Smedbol. But there are few farms facing on St. Mary’s Bay, and the Municipality of the District of Digby has said there are no municipal sewage or water systems in the areas where the dead fish have been found.
Smedbol also points out that St. Mary’s Bay “basically empties and refills once a day, so if it was a one-off event it might have already washed out of the bay.”
The new tidal turbine has also been suggested as a possible source of the marine deaths. The five-story turbine began generating power in November. But there is no evidence that indicates the turbine has played a role in the deaths. Not only that, but the turbine is 160 kilometers away from where the animals have been washing up on shore.
Smedbol also points out that if the tidal turbine were responsible, there would be other fish species affected and the DFO would be finding more fish washing up on beaches in other areas. But Smedbol does wonder if a recent winter storm that hit the area could have played a role in the marine deaths. The storm dropped water temperatures near the shore to –5 degrees Celsius in the shallows.
Smedbol said that combined with rough surf, it could have caused bottom-dwelling sea creatures to die and wash up. “It is a little bit perplexing and now we’re broadening out our analysis again, looking at things that might be less likely.”
