The discovery in August of 27 dead harbor seals stranded on Stratton Island (in Saco Bay) prompted the National Oceanographic and Atmospheric Administration (NOAA) to reopen a previous investigation to determine the cause of unusual seal deaths along Maine’s coast.
NOAA officials began looking into the problem last fall, after 66 adult harbor seals were found dead (most from September to November) between midcoast and southern Maine. According to the Marine Animal Lifeline, a private, nonprofit organization authorized by the NOAA Fisheries group to respond to reports of stranded seals in southern Maine, 66 dead harbor seals is almost twice the number that would usually would have been reported that time of year. The results of last year’s NOAA investigation were inconclusive.
According to Greg Jakush, founder and president of the Marine Animal Lifeline, the Maine Audubon Society contacted Lifeline on Aug. 17 regarding a group of seal carcasses found on Stratton Island. A team from MAL initiated an investigation in response to that report but the carcasses were already badly decomposed, which made it difficult to know for certain what caused the deaths.
“We were called and we responded the same day but the bodies were in the advanced stages of decomposition,” said Jakush.
Greg Earle, onsite coordinator for NOAA’s Unusual Mortality Events (UMEs) in Maine, confirmed in October that the Stratton Island deaths were still under investigation.
“We’re still looking,” Earle said in October. “So far we haven’t found anything that’s glaring. We haven’t found any toxins and no indication that the seals were shot or injured or that kind of thing. There’s always a chance that we might find something further down the road.”
Earle explained that stranding may occur for a number of reasons. He said that it sometimes occurs during the first few months of a seal pup’s life as the pup learns to adapt to the world around him. Stranding may also occur when marine animals become sick or injured. He said that the Stratton Island situation was unusual because they didn’t find any sick seals. They only found a large group of dead seals.
“That should send up some kind of antenna,” said Earle.
He noted that it appeared that the seals died while all grouped together on their hollows, where they go to rest, as opposed to where they were feeding. That was one reason that he doubted the seals had died from ingesting something like red tide toxin, which is so toxic the seals would probably have died as soon as they ingested it.
Although Earle is doubtful that the Stratton Island occurrence was related to red tide, it’s notable that officials from Maine’s Department of Marine Resources (DMR) reported finding shellfish that tested positive for red tide toxin in the same vicinity as the Stratton Island seals, during the same time period that the strandings were reported.
According to DMR scientist Laurie Bean, the coast extending from Ogunquit to Cape Elizabeth was closed to mussel harvesting from Aug. 9 until Sept. 29 due to red tide.
“The closure was promulgated on Aug. 9 and repealed on Sept. 29,” said Bean. “There was a big hit in August. A lot of that area was toxic.” Bean added that the type of red tide toxin found in that area was the type causes paralytic shellfish poisoning. She didn’t indicate whether they tested for any other type of toxin during that time period.
“Beach Watch: A Shoreline Survey Program,” a science feature that appeared on the National Marine Sanctuaries’ website in October, described three red tide events that occurred off the coast of central California between May 17 and June 2, 1998. Authors Jan Roletto, Joe Mortenson and Leslie Grella noted that “During the red tide events, the stranding of dead common murres and otalids (fur seals and sea lions) greatly increased above the rates previously documented for this region during the months of May and June.” Some of the stranded seals were said to be Pacific harbor seals.
The California red tide events were reportedly related to certain species of marine algae containing domoic acid, a toxin that causes amnesic shellfish poisoning. However, the toxic and harmful algal blooms page on the Bigelow Laboratories website indicates that seals may be affected by the red tide toxin that causes paralytic shellfish poisoning, too.