miércoles, 27 de mayo de 2009
Caught Stealing Fish?
For years, fishermen in Alaska wondered why their catches were mysteriously disappearing, and now remarkable new footage shows a sperm whale adroitly "stealing" fish on lines without leaving behind any tell-tale evidence, save for its candid camera appearance.
Watch video of the sneaky whale thief here.
The video presents the first known footage of a male sperm whale eating in the wild. Since it includes ear-splitting sounds made by the feeding whale, the video is also helping scientists better understand how the marine giants vocalize, allowing researchers to estimate population sizes based on whale chatter.
"We definitely did a high-five when we saw the video," project leader Aaron Thode of Scripps Institution of Oceanography told Discovery News. "It was a fist-pumping moment."
With the help of black cod longline fisherman Kendall Folkert, Thode and colleague Delphine Mathias deployed video cameras and acoustic recorders like flying kites on Folkert's fishing lines off Sitka, Alaska, at a depth of 328 feet. Longline operations consist of a main fishing line draped across the ocean and fastened with shorter lines bearing baited hooks.
Marine mammals often avoid anything that looks foreign in their environment, so the researchers camouflaged their setup with "fake tangled rope" and other disguises. One male sperm whale fell for the camera trap.
The video, described in the current Journal of the Acoustical Society of America, shows the sperm whale plucking a short fishing line at one end to jar a black cod at the other end free.
"It's comparable to someone shaking apples from an apple tree," said Thode, who added that the whale then "cleverly figured out how to remove its jaw away from the line, avoiding entanglement."
During the theft, the whale emitted rapid-fire clicks -- "louder than a firecracker" -- that got faster as it approached the cod. The scientists now believe sperm whales may produce the animal kingdom's loudest and most intense sounds.
The footage also permitted the first-ever direct comparison between sperm whale clicking and physical features of the noise producer's head. "We now know that the larger the whale's head is, the longer its clicks will be," Thode said.
The firecracker analogy might not be too far off, since he explained the huge rectangular-shaped top of the sperm whale's head contains the spermaceti organ, which produces a white, waxy substance formerly used by humans to make candles and ointments. In this case, it facilitates the movement of sound that "ricochets back and forth within the whale's head, knocking against the skull."
The researchers detected several "mini clicks" within each audible whale click, all of which are part of the marine mammal's echolocation system. The produced sound bounces off of objects, such as the cod, and returns as an echo back to the whale, permitting him to determine the cod's size and location.
Since each whale appears to have its own unique clicks and vocalizations, Thode believes it will soon be possible to record whales underwater and tease apart their sounds. Researchers might then more accurately count whale populations, which could improve conservation efforts and help to prevent future whale and longline encounters that can be dangerous for both the toothed whales and fishermen.
In a separate study, University of California's David Lindberg and his colleagues determined that sperm whales evolved their elaborate echolocation methods in order to "develop a complex system with finer resolution to detect and capture soft-bodied squid." Some giant squid can grow to lengths of 40 feet, providing a hard-to-resist treat, not unlike the longline dangling black cod seen in the new video.
"Some of my friends think the video looks like a fake shadow puppet show," Thode said, "but I assure everyone it's real."