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USF scientists rock and roll in rough Antarctic seas; silverfish are scarce

Gravity and ship motion have been high on our awareness list for the past couple of days.

I'm here to tell you that the Drake Passage does not have the corner on high winds. It was blowing 60 knots for much of Saturday night; for a while, it was like an amusement park ride.

For those of you who have not experienced a squall at sea, imagine riding a fast elevator in a tall building — but the elevator is moving rapidly up and down in a twilight zone between, say, the 12th and 15th floors.

Add in a couple cups of roll, a pound of pitch, and a dash of yaw (you'll have to look that one up), and shake vigorously. Then you have the feel.

In the end, some gear was damaged, but with our backups we are okay.

In our transit north from Marguerite Bay (see map in gallery), we stopped briefly at Rothera Base to pick up some cargo and have a quick tour. Then we made our way to Renaud Island for sampling.

Our investigation thus far has revealed that silverfish pretty much stop at Marguerite Bay. There were none at Renaud, but they were fairly abundant down south at Charcot and in Marguerite Bay.

They were formerly quite abundant in our present location, near Palmer Station, but we have now sampled in three places (and the penguins in many more) and the silverfish are just not here.

Why does it matter that one fish seems to be disappearing over part of its range? It's just one fish, right?

It matters because in the vast majority of the coastal Antarctic, the silverfish is one of only two fishes that spends its entire life in the pelagic realm: the "midwater" between the surface and the bottom. The only other pelagic fish is quite large — it gets to 3 feet or so.

For a contrast, in Florida coastal waters we have several species of sardines and anchovies alone.

Think of the silverfish as the Antarctic sardine, and then think of it as the only fish available for seabirds to eat in most of the coastal Antarctic. It is a staple of seals as well.

When an important food source like that disappears, its predators suffer. The Adélie penguins near Palmer have declined by well over 50 percent in numbers over the past 25 years. Coincidence?

As we have moved north, the surface ocean has warmed considerably, from 30 to 34 degrees Fahrenheit. The air temperature has varied from 28 to 35 — balmy by Antarctic standards for this time of year, but still cold when working in it.

Our next stop, Croker Passage, is important because we know from a netting survey that there was a healthy community of silverfish there in 1983. Will there be silverfish now? We'll see.

USF scientists rock and roll in rough Antarctic seas; silverfish are scarce 04/20/10 [Last modified: Tuesday, April 20, 2010 2:38pm]
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