The three types of killer whales. From R. Pitman, P. Ensor, J. Cetacean Res Manage 5(2):2003.

Ross Sea killer whales appear in the McMurdo Sound area and the southern Ross Sea, in early December and ply various fast ice edges (ice attached to the land), which as the season progresses recede further and further south toward the continent. They also apparently forage under or along the edge of the Ross Ice Shelf by Cape Crozier on the other side of Ross Island. These whales feed on fish that live under the fast ice and as the ice recedes the whales are able to exploit more and more feeding territory. Sightings of these whales, from land, helicopters and ships have been carried out through the years, most recently from the Cape Crozier and Cape Royds penguin colonies on Ross Island, where it has been noticed that the presence of whales (including minke whales) follows a shift in the diet of the penguins.

Killer whales foraging in a sea ice crack.

In 2005 the ratio of C to B killer whales was 50-1, but over the next few years it steadily dropped to 16-1 by 2008. As the observed numbers of B whales (seal eaters) did not change during this time, the altered ratio was due to the decrease in Ross Sea killer whales. During the years of these observations another important series of events was taking place.

Although commercial fishing of the Antarctic toothfish (sold as “Chilean sea bass”) in the Ross Sea began in 1996, it was expanded in 2004 from 9 to 22 fishing vessels; not surprisingly that same year the catch reached its allowed limit of 3500 tones. These boats target the largest adult toothfish, which is the same size those taken by the whales. Toothfish are a slow growing species which do not reach maturity until 16 years old. Many of these fish taken in the fishery were over 25 years old, some older.

Antarctic toothfish.

Since 2004, the commercial catch has remained steady year by year. Catch and release efforts of toothfish by scientists in McMurdo Sound remained steady from the years 1974 to 2000, but dropped 50% in 2001 a few years after the commercial fishing began and then to 4% in 2007, only 3 years after the peak commercial catches began. It would appear that the drop in Ross Sea killer whale numbers is related to the increase in the commercial fishing of the toothfish.

Are there any other animals that would be affected by the reduction in toothfish numbers?

Weddell seals also take toothfish as a primary food source and their numbers have not decreased in McMurdo Sound, though trends elsewhere along Victoria Land are unknown. Seals are able to dive deeper and stay under longer than the whales and therefore able to catch the fish which are safe from the whales. Seals therefore not only forage where the whales forage, but also in areas the whales can not reach, places covered with extensive fast ice where small cracks provide breathing holes. Seals also eat silverfish. It is thought that whales also eat silverfish but there are no confirmed sightings for this. The whales therefore may be more sensitive to changes in toothfish availability. If the toothfish industry continues to extract the current yearly numbers, it is predicted these creatures will decline more rapidly.

For more information about the Ross Sea, the toothfish industry and how it is affecting penguins, whales and seals go to The Last Ocean.

For some time it was thought that Weddell seals did not eat the toothfish and therefore would not be affected by the reduction of these fish in the ocean. The fishing industry has pushed to increase catch limits based on this assumption. We’re learning, though, that this is not true by indirect means.

One way researchers determine what an animal eats is by sorting through their scats (body waste). Indigestible parts pass through the body of seals and whales and can be identified. In the case of fish, the ear bones, or otoliths, are used to determine not only what species of fish are eaten, but how old and large they are. Toothfish otoliths have not been found in seal waste. But recently we’ve learned why.

Antarctic Toothfish ear bone (otolith).

As is the case with many discoveries chance plays a large part. While out on a diving expedition one researcher discovered the heads of many toothfish near a crack in the ice. The only predators in the area are seals, so these heads must be the remains of their meal. No wonder there are no otoliths in the seal waste, they don’t eat the heads! By observing seals in holes drilled through the ice for scuba access, it has been observed that seals remove the heads so this information was already known. But many people still doubt the implications of this or contend that it is a ‘local’ phenomenon. Finding these heads, in the company of seal holes, was another clear indication that this belief is wrong. Retrieving these heads would also mean that scientists could remove the ear bones (otoliths) and determine the age of the fish as well as where the fish grew up (one of the many mysteries about toothfish that remains unsolved).

The crack, where seals come to find toothfish hiding under the ice.

The helicopter landed us in this remote place on the McMurdo ice shelf.

So off we go. First a helicopter ride to the place where the fish heads were first found, and then a 10 km walk over and around the rough terrain along the crack in search of other evidence. All in all the remains of 30 fish were found, and 20 heads were brought back to the lab to extract the otoliths.

Antarctic toothfish heads, the remains of a Weddell seal feast.

Searching for Antarctic Toothfish heads on the McMurdo Ice Shelf crack.

Bagging Antarctic Toothfish heads.

As it turned out, most of the heads had become mummified, i.e. freeze-dried, and acidic action in the flesh during the process of decomposition in many cases dissolved the otoliths. There were just little ‘puffs’ of white stuff where the otoliths should have been. Skuas had eaten the otoliths in other of the heads. But, we did find otoliths in 6 heads, and these will be tested and analyzed in a lab in the US. Providing evidence to fishery biologists that toothfish are an important food source for seals will help the argument to limit the commercial catch.

Learn more about Antarctica toothfish and conserving the Ross Sea for all marine organisms by visiting The Last Ocean.

We heard that sound again two days ago at Cape Royds, having heard it before in January 2005, when a several square kilometer opening appeared in the fast ice just offshore in a matter of hours. The ice was dissolving, or would we call it melting?, and it was happening so fast that you could see it disappearing without even needing your imagination to be going overtime. It’s kind of like putting an ice cube in a cup of boiling tea water to watch it disappear; only here the water is just a degree above freezing. That’s plenty warm as ice goes. In 2005 the fast ice was thinner, so it went from white ice to blue water; this year it was much thicker, so for a couple of weeks it slowly turned darker shades of gray, as it took on more water. Then, fzzzzzzz.

Otherwise, except for this new patch of open water within the ice, called a polynya (a Russian word; without a doubt the Inuits have a name for this, too), there is still fast ice to the horizon as I have described in various of my previous dispatches.

The Swedish icebreaker Oden going south, very slowly, through the ice a few kilometers out in McMurdo Sound, while a polynya begins to form next to Cape Royds.

The south ‘shore’ of the polynya, the day after it initially formed, showing proximity to the Cape Royds penguin colony (tan area on left side of image). The polynya is to the right, beginning to dissolve the gray ice in the center of the image.

In fact, in the Arctic, Inuit villages — and, for that matter, seabird colonies — are located near to polynyas. And, wouldn’t you know, so are penguin colonies, although at the opposite end of the Earth. This is because polynyas allow these predators much easier access to their food. Normally, McMurdo Sound is one big polynya, and the penguins are here at Royds because of it. As I’ve been making the point in previous dispatches, the Royds penguins have been having a hard time of it this season, because their polynya didn’t form, owing to calm winds which allowed the ice to thicken until not even the strongest winds could blow it away. So, they’ve had a very long walk to get food. That is, up until a few weeks ago, when the few remaining penguins still having chicks were provided a large crack to feed in, just 4-5 km north of the colony. Now they’ve got a full-fledged, mini-polynya and all is right in the World!

Well, just like in 2005, within a day of the polynya forming, a couple of minke whales showed up in it! Where they came from, I’m not sure, but they may have followed the Oden into the ice (35 km from the fast ice edge), and then pealed off when a crack that intersected the icebreaker channel allowed them to get to the Cape Royds polynya. Maybe they heard it fizzing! Or the sounds of joyful penguins!

The minke whales, for several hours, cruised around the polynya feeding all the time. They’d submerge for 6-8 min at a time and likely were like big “Hoovers”, i.e. vacuum cleaners. Between dives, they exhaled (i.e. whale “blows”) 4-5 times, clearly audible in the still air from a kilometer away. Within a couple of hours after the whales’ arrival, the penguins’ diet switched from krill to fish. I’d been monitoring it by watching what passes between adult and chick everyday for the past few weeks. Wow! I knew that the whales could do this to the penguins, but I didn’t realize that the whales were so efficient! Not long after the whales left (they’ve not been seen for about 24 hours now) the penguins’ diet switched back to krill. Therefore, this is pretty good evidence for what we call “interference competition”. The whales certainly eat a lot but also their vacuuming causes the krill to try to escape, of course. And what krill do when being pursued, if they can, is to dive deeper and, it seems, deeper than penguins want to go, especially when there are enough fish to be had at shallower depths, though apparently not in a density that in this case would interest a minke looking for easy pickings. If the whales had vacuumed all the krill, when they left, there would be no food for the penguins. As it was, the krill ventured back up into the light (where the phytoplankton occurs that the krill eat), to then be caught by the penguins again. Both whales and penguins go for the easy meal, i.e. that nearest the surface.

Parent feeding its chick. With binoculars, if you get the right angle, usually it is possible to determine whether krill (pink) or fish (gray) is being fed to the chick.

Well, so, you’d think that maybe whales are an annoyance to Adélie penguins. As it turns out, though, minke whales are life savers! Adélie penguins, if given a choice, would always want to have minke whales around, despite the whales’ appetite and despite the best (?) efforts of the Japanese whalers. You see, minke whales — because, like Adélie penguins, they are pack ice denizens — have evolved a very long and sharp “beak”. When you see the whales in areas were the sea is freezing, it becomes quickly obvious why this is a good thing. The whales use their rostrum to break breathing holes in the new ice.

This ice is thick enough that penguins walk over it. With the whales around, though, the penguins can swim between whale breathing holes much faster than walking. In fact, several years ago, when on an icebreaker at the time of ice freeze-up in the Amundsen Sea, one day there were whales and penguins swimming around, and then the next day, with a dramatic drop in temperature and a freeze, there were whale holes but no whales or penguins. Together, they had escaped north far enough to move away from the area of freezing.

A minke whale pushing up through recently frozen sea ice, the ice around it being 4-5 cm thick.

All but one of these penguins found a hole left by a minke whale; the next whale breathing hole is just behind the lone penguin and this flock of penguins is next going to appear in that hole.

These penguins are not walking on frosted glass. They are walking on ice thick enough to support their weight, but not thick enough that a minke whale could not break a hole.

It is good for Adélie penguins to have as many minke whales around as possible. This one, like the pied piper, is making a “channel” through new ice, soon to be followed by a flock (school?) of penguins, who would much rather swim than walk.

Penguins need whales, especially minke whales, as friends.

At Cape Royds we watch to see what the adults are feeding their chicks. If it is pink, then the main portion of the food is krill, if it is silver then it is fish. But what kind of fish? That is where the penguin poop tray comes in. At the end of last season we set out a large tray with a fine mesh in an area where penguins have regularly nested. After the breeding season was over and the nesting adults and chicks were gone, the tray was full of penguin guano. Several washings and sortings to eliminate the large stuff later, we sift through the rest looking for otoliths (fish ear bones) which will tell us what kind and how old the fish is. The bones do not get digested so they are passed through. It’s messy work, but important knowledge to gain about Adelie Penguins and their eating habits.

A new otolith tray set out in the field waiting for penguins to make their nests.

Luckily two penguins decided to nest in the tray. Lots of guano for us.

A season’s tray of penguin guano washed and sieved and ready for sorting under the stereoscope.

Now the work begins. It takes hours to look for the tiny bones.

An otolith, less than a millimeter long.

Antarctic krill, Euphausia superba, is the largest krill species.

Adélie penguin nesting areas on Avian Island, stained red due to the penguins’ highly krill-based diet.

Dip a net into coastal Antarctic waters and you’re likely to pull up more than a few pinky-sized shrimplike crustaceans. These are krill, and if they look like small-time players in the game of life, it only goes to show exactly how deceiving looks can be.

The Antarctic food web is the simplest on the planet, and krill are at its hub. An estimated 500 million tons of krill live in the Southern Ocean, making this the most abundant animal in the entire world. Krill are such a universal food in Antarctica that for almost every animal that lives here, a “three degrees of krill” rule applies: You are krill, or you eat krill, or your food eats krill.

Whales, seals, penguins, albatross, petrels, fish, squid—every animal species living in Antarctica depends directly or indirectly on krill for survival. This heavy reliance on a single species makes the Antarctic ecosystem an unusually fragile one, particularly since many animals—including baleen whales such as the humpback, fin, minke, and blue whales—eat krill almost exclusively.

Krill, in turn, filter-feed on the abundant phytoplankton in the open ocean. In winter, they also gorge themselves on the ice algae that grow on the underside of the pack ice. A single krill can scrape clear the algae from a square-foot (.09 m²) patch of ice in ten minutes, zigging and zagging back and forth lawn mower–style.

Corethron, a type of phytoplankton, highly magnified under the microscope.

This image, taken by a remote operated underwater vehicle (or ROV), shows how most krill feed by swimming upside-down directly under the ice, grazing as they go.

Extra cold winters are a boon to most animals living in Antarctica. Colder winters mean more pack ice, and more ice algae to feed more krill, which means more food for all. In warmer years, when the pack ice is reduced, there’s a measurable decline in the krill population, sending shock waves of scarcity through the shallow Antarctic food web.

Even in good years, competition for krill can get fierce. Biologist David Ainley discovered that minke whales drive Adélie penguins from the best krill feeding zones, forcing the penguins to venture farther afield or switch to hunting fish. Humans have also joined the fray, using nets to harvest roughly 100 million tons of krill each year for use in animal feed, dietary supplements, as fish bait, and also for direct human consumption.

Researchers fear that global warming and dwindling pack ice are likely to pose serious challenges for the Antarctic ecosystem. In the short term, however, there is one perk to warmer temperatures: an increased number of icebergs. Marine scientist Maria Vernet has found that these floating oases deliver nutrients to the surrounding water as they melt, creating flourishing (if temporary) mobile ecosystems on and around the bergs.

Cassandra Brooks is a marine scientist and science writer based in California. She’s studied Antarctic marine resources since 2004 at Moss Landing Marine Laboratories (MLML) and with the Antarctic Marine Living Resources (AMLR) Program.

Cassandra Brooks first began studying Antarctic toothfish in 2004 as part of her master’s thesis at Moss Landing Marine Laboratories. Antarctic toothfish are large, deep-sea predatory fish found only in the ice-laden waters surrounding Antarctica. Biologists who were fascinated with their ability to live in these freezing waters were the first to study these fish. It turns out that Antarctic toothfish have special proteins in their bodies that act like anti-freeze to keep their blood from freezing, thus enabling the fish to live in the icy waters off Antarctica.

Commercial fishermen took notice of the Antarctic toothfish only in the last ten years when populations of its sister species, the Patagonian toothfish, became depleted. Patagonian toothfish are found in the northern waters of the Southern Ocean, off the tip of South America and around sub-Antarctic islands. Both species of toothfish are more commonly known by their market name “Chilean Sea Bass,” though they bear no relation to sea bass. The depletions of Patagonian toothfish were likely caused by the large illegal pirate fishery, which has been estimated at up to 70 percent of the total harvest of this species.

As the subantarctic waters where the Patagonian toothfish lives were overharvested, vessels moved further south, into the remote and pristine waters of the Ross Sea, Antarctica, in search of the Antarctic toothfish. The commercial catch of Antarctic toothfish has increased steadily over the last ten years, even though very little is known about the basic biology of this fish. Cassandra’s work focuses on life history and population structure of this species. Her goal is to provide information on their age, growth, and spatial distribution to the toothfish’s managing body (CCAMLR) in order to facilitate sustainable management of this large Antarctic species.

Antifreeze Fish

Some of the coldest ocean waters on earth, where temperatures fall below the freezing point of fresh water, are found in the Southern Ocean surrounding Antarctica. Nearly every fish on the planet would freeze to death if it tried to brave such harsh conditions. The Antarctic toothfish, however, thrives in this icy environment. How does it do it?

Antarctic toothfish have evolved remarkable traits that allow them to survive in sub-freezing waters. One of these traits is a slow heartbeat—a beat only once every six seconds. The main secret of these unique fish, though—who have a natural lifespan of 40 years and can weigh in at over 200 pounds when full-grown—lies in a special protein that acts like antifreeze. By making this unique antifreeze glycoprotein, the Antarctic toothfish are able to keep their blood from freezing. It’s a remarkable evolutionary solution to surviving in the frigid waters of the Antarctic.

One of the most amazing things about these Antarctic antifreeze fish is their corollary in the Arctic, where waters reach similar subfreezing temperatures. There, fish carry a similar but different antifreeze protein—evolutionarily distinct from that of the Antarctic toothfish. What this means is that fish at both ends of the planet evolved similar antifreeze survival strategies through completely different methods.
For more on this awesome evolutionary achievement, please visit our Origins site here.

Background on AMLR

The United States is one of 25 nations that are bound by the Convention on the Conservation of Antarctic Marine Living Resources (CCAMLR). CCAMLR is an international treaty, the aim of which is to conserve marine life in the Southern Ocean and to ensure the harvesting of marine resources is done in a sustainable manner without disrupting the Antarctic ecosystem. The United States Antarctic Marine Living Resources (AMLR) program is responsible for collecting scientific information that will be used to develop and support US policy regarding the conservation and management of the marine resources in the waters surrounding Antarctica. For over 20 years, scientists with the AMLR program have investigated the effects of krill, crab and finfish fisheries on the ecosystem, including the effects on seal and seabird populations. The Antarctic Ecosystem Research Division (AERD), located at the Southwest Fisheries Science Center branch of NOAA Fisheries, manages the AMLR Program.

When Cassandra goes to sea with AMLR, she primarily studies zooplankton under Dr. Valerie Loeb, a marine biologist at Moss Landing Marine Laboratories (MLML) and a contact scientist for AMLR. Valerie studies the abundance, demography, and distribution patterns of krill, and is head of the krill and zooplankton component of the AMLR program. Valerie and the AMLR crew study krill because these small (approximately 2–2.5 inches, or 5-6 cm) shrimp-like crustaceans are the most abundant and important food source in Antarctica. The whales, seals, fish, and seabirds in the Southern Ocean all depend on krill for their survival.

About 10 years ago New Zealand decided that the Antarctic toothfish, known to the rest of the world as Chilean sea bass, should be extracted from the Ross Sea. It’s the last place left on Earth where the ocean fish have not been depleted. After five years of “experimental fishing” by NZ, a full-fledged fishery was launched. This now includes about a dozen countries and 21 fishing vessels. Despite their charter to protect the living resources of Antarctica’s seas, CCAMLR instituted no procedures for monitoring the impact of the fishery on the ecosystem. So we’ve taken it upon ourselves to come up with some procedures by which this can be done.

Adult Chilean sea bass (on snow) and subadult (held by person) caught through a hole in the fast ice of McMurdo Sound.

Antarctic silverfish, which both Chilean sea bass and Weddell seals eat in the Ross Sea.

Weddell seals eat a lot of toothfish and the best-known population of these seals, and perhaps the best-studied pinnipeds population in the World, is in southern McMurdo Sound, in the vicinity of Cape Royds. Thus, with the seal folks from Montana State University, we submitted a procedure to CCAMLR last summer to monitor the seal population using aerial photography. The idea is that as more Chilean sea bass are taken from the Ross Sea, the seal population should change. Seal numbers would either decline because there are fewer sea bass to eat or increase because with fewer sea bass there would be more silverfish for the seals to eat (the fish and the seals also compete for Antarctic silverfish).

Weddell seal mom and pup, Erebus Bay, McMurdo Sound

Weddell seal with toothfish (Chilean sea bass) that it captured, and which it is beginning to consume.

CCAMLR accepted our aerial protocol but then told us we had to demonstrate its utility in the field. This led to our aerial flight. To say the least, with aerial photography having been used to count seals in the Arctic for decades, our counts from the air were close in number to those counted on foot two days previously. We’ll now submit a report to CCAMLR and hopefully the fishing industry will take the responsibility to begin at least one measure to keep track on how their fishing may affect the ecosystem of the Ross Sea.

Weddell seals spread along a tide crack in Erebus Bay; view from 1000 ft.