The number of brant geese overwintering in Morro Bay has steadily diminished over the past decade.
John Roser, a volunteer who counts the birds monthly during their six-month stay here, said the birds’ numbers have dropped 76 percent since a peak in 2001-02. Although the winter is only half over, the numbers of brant appear to be down this year as well.
“There has been a steady decline for the last 10 years,” he said. “It looks like the trend is continuing.”
The brant is a small goose that feeds in sheltered bays along the coast during the winter and breeds on the high arctic tundra during the summer. Roser has been monitoring numbers of the birds in Morro Bay for the past 15 years and is puzzled by the trend.
“I don’t know what is causing this decline,” he said.
Possible explanations include global climate change and a reduction in the amount of eelgrass in the bay, the birds’ main food source. Also, rising global temperatures have caused the birds’ jumping-off point in southwestern Alaska to be ice-free, meaning the birds do not have to travel this far south to find food.
A shift in storm patterns may also be a contributing factor. Storms provide tailwinds for the brant as they migrate down the coast.“There has definitely been a shift northward,” Roser said. “Some years, a third of the population is wintering up in Alaska.”
A report recently published by the Morro Bay National Estuary Program said the amount of eelgrass in the bay has dropped by 49 percent since 2007. This, too, could be contributing to the declining brant numbers.
There is no clear reason why eelgrass acreage has dropped, said Annie Gillespie, the estuary program’s monitoring manager.“There’s no obvious smoking gun,” she said. “We know that there was some loss due to the tsunami surge and then last winter we had a lot of rainfall that boosted sedimentation.”
Although the March 11 tsunami from a massive earthquake in Japan was barely noticeable along the open coastline of the county, it caused intense tidal surges within Morro Bay for about three days after the quake.