Climate change killing Antarctic silverfish?

This 2015 video says about itself:

NIWA scientists aboard RV Tangaroa have been trawling the central Ross Sea calculating the abundance of the prey species.

The trawl through the Antarctic waters at about 72 degrees south, concentrates on the area where about 3000 tonnes of toothfish are harvested each year. The catch revealed rattails, icefish, glacial squid, and silverfish and a number of unusual fish and invertebrates.

While the scientists are less interested in the toothfish than in the health and abundance of the fish they feed on, they did catch a healthy specimen during the trawl. The fish was measured, tagged and released according to CCAMLAR protocols.

Tangaroa is four weeks into a six-week research voyage investigating the food webs that support the oceans top predators – humpback whales, blue whales and toothfish.

From The Antarctic Sun:

Fishy business

Climate change may be to blame for disappearance of Antarctic silverfish

By Peter Rejcek, Antarctic Sun Editor

Posted July 9, 2010

Adélie penguins across parts of the northwestern Antarctic Peninsula don’t appear to be getting a balanced diet these days.

What’s missing? A sardine-sized fish called Pleuragramma antarcticum, more commonly referred to as the Antarctic silverfish.

Once upon a time, as the story goes, Antarctic silverfish swam by the thousands in places like Arthur Harbor at the northern end of the peninsula.

“That doesn’t happen anymore,” said Joseph Torres External Non-U.S. government site, a professor in the College of Marine Science at the University of South Florida External Non-U.S. government site. Torres led a diverse team of biologists, oceanographers, geneticists and others to the region earlier this year to find out exactly what’s happened to the silverfish.

It’s been about 15 years since any significant numbers of silverfish were found in the Adélie diet in the area around Palmer Station on Arthur Harbor, according to Bill Fraser, whose work in the region dates back to the 1970s and is part of the Palmer Long Term Ecological Research External Non-U.S. government site program funded by the National Science Foundation (NSF) External U.S. government site. The NSF also funded the silverfish expedition.

The scientists traveled aboard the research vessel Nathaniel B. Palmer External U.S. government site, steaming about 1,200 kilometers along the western side of the peninsula, starting south at Charcot Island to the northern tip at Joinville Island, stopping at several key penguin colonies along the way.

“What we wanted to do was contrast the different regions in terms of how many silverfish they had and what the diet of the penguins there was like,” Torres explained. “We were curious if the penguin diets reflected what the community was like out there.”

Expected results

The scientists used two methods to search for the disappearing silverfish. They towed nets from the ship along the relatively shallow waters of the continental shelf near where penguin colonies forage for food. And Fraser’s seabird researchers visited key penguin colonies on various islands. They examined the stomach contents of nearly 60 birds, as well as attached satellite tags on some penguins to monitor their foraging habits.

They found silverfish where they expected to find them — in the south, where sea ice and a colder climate persist. They didn’t find them where they expected not to find them — around Palmer Station farther to the north, where ambient winter temperatures are up about 6.5 degrees Celsius since the 1950s and sea ice is a fading memory.

Like other parts of the polar food web — such as Adélie penguins and shrimp-like krill — the silverfish rely on sea ice for parts of their lifecycle. For example, the sea ice offers cover when the eggs hatch in November, Torres noted.

Without it, he added, “the larvae are exposed to predation in the open water.”

Based on the preliminary results of the net tows and diet samples, Fraser said, “I think we can pretty substantially confirm that the silverfish have, in fact, disappeared from a very specific region of the Antarctic Peninsula, which happens to be the region that has experienced the most rapid winter sea ice loss over the last three decades.”

On the other hand, silverfish still account for a substantial part of the the penguin diet for birds at Charcot and Avian Island to the south. While still awaiting more definitive analysis, Fraser said he estimated that Pleuragramma made up about half of the meals for birds on Avian and upwards of 80 percent for the most southerly Adélies at Charcot.

Outclassed

But the story is more complicated — and possibly grimmer — than the scientists first suspected. While they found Antarctic silverfish in the south, they saw fish dominated by only one age class, a cohort they estimate to be about 9 or 10 years old. The absence of a younger age class, a new generation, is worrisome, according to Torres.

“It tells me that the population isn’t getting any new recruits,” he said. “What we’re looking at is a population that is not a healthy one.”

In fact, the only bright spot was around Joinville Island in the extreme north, where currents from the Weddell Sea bring in new silverfish from the still healthy populations on the eastern side of the peninsula. But thickening sea ice and blustery weather that dropped the wind chill to minus 50 degrees centigrade made for challenging working conditions there.

Penguin males with steady pitch make better parents: here.

What is causing bizarre penguin deaths in Brazil? Here.

Most penguin populations continue to decline: here.

Ecologists fear Antarctic krill crisis: here.

‘Sardine Run’ off South Africa a spectacular diving experience: pics here.

Related articles

• ‘Tiger stripes’ underneath Antarctic glaciers slow the flow (phys.org)
• Climate change winner: Adelie penguins (stuff.co.nz)
• ‘Speed bumps’ below help control Antarctic glacier flow (nbcnews.com)
• Antarctic research program on ice due to government shutdown (stripes.com)
• The Government Shutdown Is Killing Antarctic Science (washingtonmonthly.com)
• Antarctic research freeze ‘a disaster for science’ (sbs.com.au)