Un artículo muy interesante sobre la investigaciones del pulpo gigante del pacífico, en la web que mantiene Nurp
(NOAA's Undersea Research Program). La NOAA es la National Oceanic and Atmospheric Administration de los EEUU.
In the Octopus's Garden
by Julie Zeidner Russo
The sighting of fantastic sea creatures like the giant octopus have been portrayed throughout history. Probably the first recorded mention of something that resembles an octopus was the monster Scylla in Homer's Odyssey. At the dawn of a new millennium, the giant octopus is not so much a folkloric figure as a culinary delicacy for the Japanese, a staple in some Native American diets, and a subject of rare scientific scrutiny.
There is still much to learn about the giant octopus beyond its role in fiction or as a food source. Taste for the giant octopus could make it subject to an eastern Pacific commercial fishery before long. This increasing demand comes well in advance of an understanding of how and where the giant octopus lives.
A wealth of information on what is known about the giant octopus can be found at marine ecologist David Scheel's web site at http://www.pwssc.gen.ak.us/~dls. Reading through the site, one learns a great deal about the largest species of octopus in the world known as Enteroctopus dofleini. Although the giant octopus rarely weighs more than 100 pounds (45 kg), a few large individuals have been recorded up to 400 pounds (182 kg). While there are more than 100 species of octopuses in the world, our knowledge of octopuses comes almost entirely from a few species, Scheel said.
An intensive effort to learn more about the giant octopus commenced after the Exxon Valdez oil spill impacted the area. The Prince William Sound Science Center (PWSSC), a nonprofit research institute where Scheel is an associate scientist, was established in response to the environmental disaster.
The institute's focus would be on ecological research associated with the Prince William Sound and Copper River Watersheds in Alaska. Their work would be important since the Sound is one of the last major glacial carved embayments on the northwestern edge of a temperate coastal zone with rainforest biodiversity. "It's a really amazing area with a very complex history of coastal peoples," Scheel said.
A coastal tradition was upset following the 1989 oil spill. The native villagers in Tatitlek and Chenega Bay eat amikuq (the Alutiiq word for octopus) as part of their subsistence lifestyle. They reported that octopuses became scarce in the years following the 1989 oil spill, Scheel said. A two-year study was launched by Scheel and co-investigators to survey octopuses from the shoreline to 30 feet. The study was paid for by the Exxon Valdez Oil Spill Trustee Council. The researchers adopted the technique used by native villagers when harvesting octopus that den under rocks and are exposed at low tide as a means of counting and characterizing octopuses. They found densities an order of magnitude--10 to one--less than a survey done in British Columbia by scientist Brian Hartwick in the '70s and early '80s, Scheel said. Researchers did not have enough information about the giant octopus to attribute this difference to the more northern study area in Prince William Sound, or to a decline in abundance from man-made causes or from natural fluctuations in abundance. "It's not clear there was any decline in octopuses," said Scheel, noting more research would have to be done to determine if there was a problem.
In 1996, researchers used SCUBA dives to further investigate where and how the octopus lives and moves, and what it eats. They tagged individuals with sonic tracking devices, and monitored their movements. "SCUBA surveys proved that octopuses were more abundant on shallow dives (to five m.) than on deep dives," Scheel said. The researchers also found an abundance of juvenile octopuses, and very few adults. Where had they gone? To determine whether depth is significant in the ecology of the giant octopus researchers would need to dive deeper.
The chance to go deeper in search of the adult giant octopus occurred in May of 1998. This would be the first time researchers ever provided descriptions of octopus habitat below SCUBA depths. Scheel and ecologist Tania Vincent, also of the PWSSC, made 27 dives in the Delta submersible with support from the NOAA's Undersea Research Program (NURP).
"Using the submersible, we were able to go down and find octopuses too small to be caught by pots or long-line," Scheel said, "as well as survey the habitats, the predators, and the prey base." Scheel and Vincent would conduct 20 1000 m long transect surveys, three dives tracking a sonic-tagged octopus, and four dives to resurvey areas explored during the earlier SCUBA research and other sites of interest.
Giant octopuses have a unique life history that is only partly understood. They live across the broad continental shelf of the north Pacific ocean in a range extending from southern California to the Pacific Northwest, across the Aleutians, and south to Japan, Scheel said. They exist in shallow waters to 200 m, and may occur deeper. What happens to them during their short life span of three to five years is not fully known.
Females lay as many as 100,000 eggs inside of a rocky den and tend to them. "They senesce and die at about the time the eggs hatch," Scheel said. The males, who move around during the mating period, also die a few months later. On hatching, baby octopuses enter the plankton till they get big enough to settle down to the bottom again. After settlement, dens are an important resource for the octopus. Dens are not only used by the females for tending to their eggs, but serve as a place to hide from other predators.
"Marine mammals that feed on octopuses include seals, sea lions, sea otters, and killer whales, at least," Scheel said. Their dens-nicknamed the Octopus's Garden-also reveal a lot about them. Researchers study the middens or refuse heaps outside the octopus den to learn more about their diets, which include crustaceans, small crabs, scallops, bivalves, snails, fish, and even other octopuses.
Prior to the NURP study, the researchers understanding of the ecology of the giant octopus in rocky habitats of the eastern Pacific came from surveys to 30 m. Determining the abundance of octopuses below 30 m would be a key part of this study. Researchers theorized that since octopuses were nearly absent from depths between 10 and 30 m. in Prince William Sound, but abundant in shallower waters, that the very shallow areas might be important rearing habitat, Scheel said. They would need data from deeper areas to compare. There also appeared to be an abundance of octopuses living in heavy kelp beds in shallow areas, which may provide shelter from predators. "We thought octopuses may be restricted by high predation risk from using habits at intermediate depths to 40 meters," Scheel said. "If this were true, we anticipated that larger octopuses would be more common in deeper water; and that there might be more octopuses of all sizes."
What researchers discovered puzzled them. During the Delta dives from10 to 200 meters, Scheel and Vincent only found a total of 19 octopuses and only one was of adult size. "Contrary to our expectations, we found that larger octopuses were rare at any depth," Scheel said, "and although we found octopuses at all depths to 200 m, we found no indication of greater numbers of octopuses as we went deeper." However, they did note changes in the denning habits and diets of the octopuses at greater depths.
In order to manage the octopus fishery, resource managers will have to learn more about the natural fluctuations in octopus populations. Japan already has a large commercial fishery for octopus. While no commercial east Pacific fishery exists yet, interest is growing in developing one by parties in Japan, Africa, Greece, Alaska, and British Columbia.
"Fisheries scientists believe it would only take small changes in market demand for octopuses to trigger an increased commercial fishing effort," Scheel said. "This creates a possibility of over-exploitation of the stock, a matter of particular concern in the Gulf of Alaska coastal areas in light of damage to octopus habitat during the Exxon Valdez oil spill in 1989 and the subsistence harvests of octopuses by native peoples."
Centuries later, the giant octopus still has the capacity to intrigue us, but whether it can endure time before it is fully understood is questionable. There must have been other giant sea creatures that existed long ago that would have certainly marveled us today had they not perished. This makes understanding great animals that we know exist like the giant octopus seem all the more precious, if not critical. "The solitary nature and excellent camouflage abilities of the octopuses make them hard to count," Scheel said. While this helps protect them against natural predators, it makes it difficult for fisheries managers to conduct stock assessments to determine how they are faring and how they might be properly managed.
"Managers are considering whether an assessment based on mapping suitable habitat would provide a means to assess the population," Scheel said. "However, even habitat mapping is limited by our understanding of octopus habit ecology. This research should improve what is known about the giant octopus, so that enough information is available to prevent octopuses from being overexploited as a fisheries resource.
Labels: Monstruos marinos