Singing Humpback Whales Tracked by their Haunting Melodies
The haunting, deep melodies that male humpback whales sing have long intrigued researchers. While complex songs echo through tropical waters during the winter breeding season, they also play at higher latitudes during other times of the year. In order to track these song patterns and learn a little bit more about the largest animals in the world, NOAA researchers have examined whale movements and have linked them to their acoustic behaviors.
Since 2007, NOAA's Northeast Fisheries Science Center (NEFSC) researchers have used year-round passive acoustic monitoring in order to study ocean noise in the Stellwagen Bank National Marine Sanctuary. This area is a feeding ground for humpback whales and other marine mammal species in the southern Gulf of Maine. Usually, humpback whales frequent the area between April and December. There, they feed on sand lance and other small, schooling fish.
Yet it's not their feeding behaviors that interest researchers; it's their singing. The acoustic behavior usually occurs form April through May, followed by a spring migration from summer waters, and from August to December before the return fall migration. During the summer, humpback whales remain in the sanctuary but generally don't sing while feeding.
"Passive acoustic tracking of humpback whales and other cetacean species provides an opportunity to collect data on movement patterns that are difficult--or impossible--to obtain through other techniques," said lead author Joy Stanistree in a news release.
In order to record the whales' voices, the researchers used an array of 10 bottom-mounted marine autonomous recording units (MARUs). These continuous, 24-hour recording units were then deployed in the sanctuary for four consecutive three-month periods during 2009. Placed three to six miles apart, the MARUs shifted seasonally to areas within the sanctuary that had high whale concentrations.
Once these songs were recorded, the researchers could actually track individual singing whales. They found that most of the singers were actively swimming; the patterns and rates of their movement ranged from slow meandering to a faster directional movement. This suggested a potential reaction by one singer to the presence of the other.
The recorded songs could be used to help researchers track the geographic distribution of these whales, an important technique in order to better protect the rare species. In addition, the researchers could also use these recordings to calculate the species abundance and enhance marine conservation.
The findings were published in the journal PLOS One.