Elephant Seals Swimming Deeper as Waters Warm

Elephant seals are in it deep due to climate change ... deep in the ocean, that is. Elephant seals from Marion Island in the southwest Indian Ocean are swimming farther beneath the surface as their prey also moves into cooler, deeper waters.

"This prey is moving down to greater depths, presumably due to the increasing water temperatures, and this is forcing the seals to follow them," explained Horst Bornemann from the Alfred Wegener Institute, in a press release.

Bornemann and colleagues from the Mammal Research Institute fit more than 30 southern elephant seals (Mirounga leonina) with satellite transmitters. The transmitters are glued like beanies to the seals' heads. They measure dive depth, water temperature, and salinity on every dive, then beam that information to the marine biologists via satellite.

The results show that the seals dive deeper in warmer water.

"We therefore assume that the animals will find less prey in warmer water masses," explained Joachim Plötz, another biologist from the Alfred Wegener Institute involved in the study, in a press release.

Diving deeper means the seals have less time to feed, since they can only hold their breath for so long.

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The next step of the study will be to prove that the seals are indeed feeding at greater depths. A follow-up study will fit the seals with a sensor that will record when they open their mouths.

The biologists noted that the Marion Island seals already live near the northern end of southern elephant seal territory. Further warming could put their survival on the island in jeopardy, though the massive marine mammals are listed as of Least Concern to the IUCN.

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Male elephant seals are up to six times larger than females and rule over large harems of females. But some females have found a way to strike a blow for aquatic feminists by mating out at sea, where the sexes are on more equal terms, reported Discovery News.

IMAGES:

Southern Elephant Seal on Macquarie Island. (Credit: Mbz1, Wikimedia Commons).

An elephant seal with a sensor on its head. (Credit: Joachim Plötz, Alfred Wegener Institute).

After placing the sensor on the animal's head, the biologists measure its body size. (Credit: Joachim Plötz, Alfred Wegener Institute).

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Invasive, Tasty Tiger Prawns Prowl Gulf Waters

Bring out the melted butter and cocktail sauce. There's an invasive species to eat.

Nearly 100 sightings of the giant tiger prawn (Penaeus monodon) have been reported in Louisiana waters in 2011, according to Houma Today, a big jump from the 25 to 30 reported in past years. Considering that some of the sightings numbered close to 100 individuals, there seems to be a growing population of the nonnative shrimp prowling Gulf waters.

This year, the U.S. Geological Survey received increasing reports of the species in Mississippi, Florida, Louisiana and Texas, marking the Lone Star State's first taste of the tiger prawn, reported the Houston Chronicle.

The invasive crustaceans can offer up to 13 inches and 11 ounces of deliciousness, which is why U.. farmers brought the prawns here from their home waters on the coasts of Australia, South East Asia, South Asia and East Africa.

The black and yellow striped prawns may have started their invasion after escaping from a aquaculture operation in South Carolina in 1988, noted the Houston Chronicle. Or they could have made their break after hurricanes Katrina and Rita in 2005.

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“There’s a certain unknown about what ecological impacts that something nonindigenous like this can have on the local environment,” said Marty Bourgeois, a biologist with the Louisiana Department of Wildlife and Fisheries, in Houma Today.

Tiger prawn are voracious predators and are known to harbor numerous diseases that could spread to white and brown shrimp, oysters, and crabs in the Gulf.

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There may be one way to lick this problem, literally. The Louisiana Department of Wildlife and Fisheries has advised fisherman that the prawns should not be thrown back into any waters other than a boiling soup pot.

“I haven’t had them myself, but I’ve been told they have a sweet flavor,” Bourgeois said.

Tiger prawns could join the list of invasive species humans seek to control by eating, like wild pigs, lionfish and nutria, noted Mother Nature Network.

The tiger prawn also fetches a higher price than many other shrimp. But Leslie Hartman, of the Texas Parks and Wildlife Department, is skeptical the economic value will outweigh the damage to the native shrimp population.

"It could be another crop, but at the expense of our native crop," Hartman said in the Houston Chronicle.

For right now, researchers are trying to track down the source of the prawns using genetic evidence.

“We’re collecting them, and we’ve got some researchers looking at the genetics,” Bourgeois said. “It may help explain if they’re spawning here or if they’re riding the current into the area somehow.”

Only adults have been found in Louisiana waters, so researchers hope they may be breeding farther south and migrating north.

IMAGES:

Penaeus monodon. (Credit: Wikimedia Commons).

Tiger prawns on sale at Borough Market. (Credit: Rudolph Furtado, Wikimedia Commons).

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