Whale of a Mystery: Number of Whale Deaths in Gulf of Alaska Trumps California Coast's Count
by Mary Miller • September 2, 2015
A sperm whale washed ashore in Pacifica, CA. (Photo by Audrey Luke/Exploratorium)
Earlier this year, the intrepid Exploratorium video team braved stench and gore to document a whale necropsy on a Pacifica beach. But it appears the whale strandings in California have been dwarfed by a record number in the Gulf of Alaska: 30 since May 2015. This constitutes what NOAA calls an “unusual mortality event” or “UME” but maybe it should be a called a VUME (or very unusual mortality event) since it’s twice as many whale deaths as the previous record.
Most of the animals that died were humpback and fin whales, known as baleen whales for the sieve-like structures in their jaws that strain small fish and shrimp-like krill. I chatted with fisheries scientist Peggy Foreman, a member of the NOAA stranding response team and she said they are investigating the whale deaths to determine the cause or causes of this UME. Whales can become entangled in fishing nets or struck by large container vessels, but that’s unlikely to be the sole cause in Alaska, which is outside the busiest shipping lanes. What the team needs is more data and they are asking the public, fishermen and other scientists to keep their eyes and ears open and report dead marine mammals in the water or on the beach where they can examine the animals and take tissue samples to help determine the cause of death.
Whenever a large number of marine mammals die, the response team will also look at whether environmental conditions, including prey abundance and toxic algae, might be a factor. In a normal summer, the chilly waters of Alaska teem with life from clouds of single-cell algae and krill to fish, birds and marine mammals. But this is no ordinary year. Since late 2014, the coastal Pacific Ocean from California to Alaska has been as much as 4 to 6 degrees warmer than usual. These unusual conditions have also favored the spread of an algae bloom containing toxins that can harm wildlife.
These environmental conditions, both the “blob” of warm water and the harmful algal blooms, can lead to lower ocean productivity and disrupt the marine food chain. Baleen whales, which feed lower in the food chain, might be especially vulnerable to these kinds of ecological disruptions. In their necropsies, scientists will look at body shape and measure blubber thickness to determine the whales’ condition, including if it was well-fed or thin when it died. It may be months or years before we know, but in at least one of the recent photos, the whale looks pretty emaciated.